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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 15:34:21 +0000Relativistic Stellar Pulsations
https://resolver.caltech.edu/CaltechETD:etd-08262008-093129
Authors: {'items': [{'email': 'lsfinn@psu.edu', 'id': 'Finn-Lee-Samuel', 'name': {'family': 'Finn', 'given': 'Lee Samuel'}, 'show_email': 'YES'}]}
Year: 1987
DOI: 10.7907/T7VS-8648
<p>This thesis consists of studies on the topic of relativistic stellar pulsations.</p>
<p><i>i)</i> A new formalism for the numerical study of <i>g</i>-modes in neutron stars is developed. This formalism avoids pitfalls associated with previous formalisms when applied to the study of these low-frequency modes. The formalism involves a new choice of perturbation variables, the introduction of an "instantaneous gravity" approximation to the field outside the star, and an energy principle for determining gravitational radiation damping times. The formalism is used to study <i>g</i>-modes that arise because of chemical inhomogeneities in neutron star crusts. <i>g</i>-mode frequencies associated with chemical inhomogeneities are found to be much higher than those associated with finite temperature.</p>
<p><i>ii)</i> The relativistic Cowling approximation, introduced by McDermott, Van Horn, and Scholl (1983) and analogous to the Newtonian Cowling approximation, is refined to make it more accurate in the regime of highly relativistic stars. The approximation is used to prove a host of useful theorems regarding the non-radial modes of relativistic stars.</p>
<p><i>iii)</i> Realistic neutron stars have a solid crust, and this will seriously affect their <i>g</i>-modes. The first steps toward developing a theory of non-radial relativistic pulsations in stars with a solid crust is reported on here: the calculation of the shear strain and stress during a pulsation, the introduction of the shear stress into the Einstein field equations as a source and to the equations of motion as a force, and the development of a Lagrangian and variational principle for studying non-radial relativistic pulsations in stars with a solid crust.</p>
<p><i>iv)</i> Solar five-minute oscillations are a weak source of gravitational radiation. The inner part of the solar system is actually in the transition zone of the solar oscillation gravitational field, and future space-based beam detectors might be able to measure the solar "transition-zone radiation." The transition-zone gravitational field is explored for four relativistic gravity theories: a spin-zero theory (Nordstøm's theory), a spin-one theory (analogous to electromagnetism), a spin-two theory (general relativity), and a mixed spin-zero/spin-one theory (Jordan-Brans-Dicke theory). From the transition-zone gravitational field, it is possible to determine experimentally the spin content of relativistic gravity.</p>
https://thesis.library.caltech.edu/id/eprint/3230Development and Evolution of Magnetic Fields in Active Regions on the Sun
https://resolver.caltech.edu/CaltechETD:etd-09052008-154229
Authors: {'items': [{'id': 'Chou-Dean-Yi', 'name': {'family': 'Chou', 'given': 'Dean-Yi'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/rkc8-g529
<p>The purpose of this thesis is to investigate the development and evolution of magnetic fields in new active regions on the sun. The major observations are digital magnetograms of the line-of-sight component of magnetic fields made with the high sensitivity videomagnetograph at the Big Bear Solar Observatory, and Hα filtergrams with the 1/4 Å Hα Zeiss filter.</p>
<p>This thesis consists of three themes. First, the separation velocity of emerging magnetic flux is investigated. I measure the separation velocities of opposite polarities of 24 new bipoles, and compare them with the theoretical values estimated by the present theory of magnetic buoyancy. The predicted velocities are higher than those observed. Second, the cooling time scale of growing sunspots is studied. I define the cooling time scale and derive it from the measurements of intensity and magnetic field strength of sunspots. The cooling time scales of the ten growing sunspots studied range from 0.5 to 9 hr. I also estimate the cooling time scale from two models, the Inhibition Model and the Alfven Wave Model, based on linear theory. Both models give cooling times of about 0.05 hr. Third, nonadiabatic effects in convective instabilities in thin flux tubes are examined. I study the convective instabilities in thin flux tubes by including a nonadiabatic term. I find that a flux tube is convectively stable for any field strength.</p>https://thesis.library.caltech.edu/id/eprint/3345Magnetic Fields and Supergranule Velocity Fields on the Quiet Sun
https://resolver.caltech.edu/CaltechETD:etd-09092008-111823
Authors: {'items': [{'email': 'haimin.wang@njit.edu', 'id': 'Wang-Haimin', 'name': {'family': 'Wang', 'given': 'Haimin'}, 'orcid': '0000-0002-5233-565X', 'show_email': 'YES'}]}
Year: 1988
DOI: 10.7907/1cja-6j65
I have carried out detailed study on the quiet sun magnetic fields and super-granule velocity fields. This thesis consists of 6 themes. 1. I studied the statistical properties of quiet sun magnetic fields, including size distribution, evolution, flux budget of magnetic flux elements, and the magnetic diffusion constant. From the observations, I derived that the magnetic diffusion constant is ≤150 km²/sec in the quiet region. I found that cancelling features and Ephemeral Regions are major sources of magnetic flux disappearance and replenishment. 2. I studied the supergranule velocity fields. Supergranule vertical velocities have a r.m.s. speed of 0.03 km/s. By observing the evolution of individual supergranule cells, I found that the average lifetime of supergranules is ≥50 hours. 3. I measured the contrast of faculae near the solar limb. The measurements show no obvious contrast increase or decrease near the solar limb. The observation fits neither the "hot wall" nor "hot cloud" fluxtube model. 4. I measured the separation velocities of new bipoles. The observed values are several times smaller than the values estimated by the theory of magnetic buoyancy. 5. I applied the local correlation tracking technique to BBSO Videomagnetogram data and detected an approximate radial intranetwork flow pattern. 6. I studied the relationship between magnetic fields and convection velocity fields. I found that ephemeral regions have a light tendency to emerge at or near the boundaries of supergranules; supergranules have the same scale, correlation lifetime and mean horizontal speed in the enhanced network region as in the mixed polarity quiet sun; the velocity of moving magnetic features that surround sunspots is consistent with the direct Doppler measurement.https://thesis.library.caltech.edu/id/eprint/3410Excitation and Damping of Solar P-Modes
https://resolver.caltech.edu/CaltechETD:etd-09092008-090628
Authors: {'items': [{'id': 'Kumar-Pawan', 'name': {'family': 'Kumar', 'given': 'Pawan'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/q6y2-3263
<p>I have carried out detailed analysis of the interaction of acoustic radiation with homogeneous turbulence in order to understand the excitation of solar p-modes by turbulent convection. The most significant outcome of this investigation is the finding that, for certain types of forced turbulences, the absorption of acoustic waves is no greater than a free turbulence, whereas the emission is always enhanced by a factor M⁻², where M is the Mach number of the turbulence. Turbulent convection in the sun is an example of this kind of turbulence. This leads to the conclusion that energies in solar p-modes, due to their interaction with the convection, should be approximately equal to the thermal energy in a resonant eddy. This is found to be in good agreement with the observations. The ideas developed in the above work have been applied to explain the recently observed absorption of acoustic waves by sunspots as well. Work has also been carried out to determine the probability distribution function for the time averaged energy of stochastically excited modes. We hope to learn about the nature of the excitation and damping processes for the solar modes by comparing this theoretically determined distribution with the observations.</p>
<p>In an effort towards resolving the overstability question of solar p-modes, I have investigated the effectiveness of 3-mode couplings, the most plausible process for limiting the amplitudes of overstable modes. The 3-mode coupling mechanism is also a good candidate for exciting fundamental modes which are found to be linearly stable, but are observed to have energies comparable to p-modes of similar frequencies. The issue of mode stability remains inconclusive due to the unknown energies of modes with period ~3.5 minutes. However, we find the fundamental modes to be damped as a result of mode couplings and hence they require excitation by a mechanism other than the overstability.</p>
https://thesis.library.caltech.edu/id/eprint/3407Outflows in High Mass Star-Forming Regions
https://resolver.caltech.edu/CaltechETD:etd-09102008-084535
Authors: {'items': [{'email': 'mbarsony@seti.org', 'id': 'Barsony-Mary-Anne', 'name': {'family': 'Barsony', 'given': 'Mary Anne'}, 'show_email': 'YES'}]}
Year: 1989
DOI: 10.7907/FDFC-0Q12
<p>In the last decade, observations of star-forming regions in the millimeter wavelength range have led to the discovery of supersonic molecular outflows from embedded infrared sources, a heretofore unsuspected, but now generally accepted, phase in the star formation process. In order to better understand the outflow phenomenon in high mass (i.e., high luminosity) pre-main sequence stars, the three sources S87, LkHα101, and S106 were chosen for closer study. Observations from the recently completed Owens Valley Radio Observatory's millimeter wave interferometer afford us the highest spatial-resolution, molecular line (CS J=2→1 and <sup>13</sup>CO J=1→0) maps of these sources to date. The OVRO maps were combined with data from the 14 m FCRAO millimeter wave radio telescope, the VLA, IRAS, and the Palomar 5 m and 1.5 m optical telescopes.</p>
<p>A synthesis of the data reveals that although all three pre-main sequence objects are the sources of powerful, ionized stellar winds, only one, S87/IRS1, currently drives a bipolar molecular outflow. The inferred mass loss rates in the winds of S87/IRS1, LkHα101, and S106 IR are 1.8 x 10<sup>-5</sup>, 1.7 x 10<sup>-6</sup>, 1.1 x 10<sup>-5</sup> M<sub>☉</sub> yr<sup>-1</sup>, with corresponding wind velocities of 160, 350, and 200 km s<sup>-1</sup>. In all cases the wind velocities are lower, and the mass loss rates higher, than for main sequence stars of the same spectral types. Radiation pressure is inadequate to drive these winds, which can be anisotropic in their velocity fields.</p>
<p>The existence of massive, large-scale (r ≈ 10<sup>16</sup> cm) disks, necessary for numerous proposed molecular outflow models, can now be ruled out. Only one of the many proposed molecular outflow models is consistent with the new observations (Königl 1982).</p>
<p>Although the observed winds can disperse a good portion of the cloud cores they inhabit, they cannot completely destroy these cores. Consequently, outflows from pre-main sequence stars alone cannot account for the dispersal of molecular clouds, as some investigators have suggested.</p>
<p>Two glaring and intriguing problems remain to be solved in this field: the origin of the supersonic turbulence observed throughout a molecular cloud, and the driving mechanism of the powerful, ionized winds found in the high-mass, pre-main sequence stars.</p>
https://thesis.library.caltech.edu/id/eprint/3433A Non-LTE Analysis of a Sample of O Stars Selected from Galactic OB Associations
https://resolver.caltech.edu/CaltechETD:etd-06132007-132124
Authors: {'items': [{'email': 'kgbudge@lanl.gov', 'id': 'Budge-Kent-Grimmett', 'name': {'family': 'Budge', 'given': 'Kent Grimmett'}, 'show_email': 'YES'}]}
Year: 1990
DOI: 10.7907/A24K-G089
<p>The tables of non-LTE line profiles and equivalent widths published by Mihalas and his collaborators [33], [7], [35] have been revised and extended to four different values of the abundance ratio He/H. Bolometric corrections have been calculated for V magnitudes. The theoretical line profiles have been fit to echelle spectrograms of 22 galactic O stars by χ² minimization. It is found that the stars with the lowest surface gravities are fitted best by theoretical spectra with unexpectedly high helium abundances (He/H ~ 0.50), while the stars with higher surface gravities are fitted best by theoretical spectra with He/H ~ 0.10, the accepted cosmic ratio. This suggests a systematic failure of conventional non-LTE, plane-parallel models for the more luminous O stars, probably as a result of the neglect of geometrical dilution.</p>
<p>The formula, log He/H = 1.1234-0.4791 log g, gives a good fit to the relation between the apparent helium abundance and log g. Using this relationship, the apparent abundances have been reduced to what are probably true abundances relative to the normal cosmic abundance. It is found that there is no significant difference in the average helium abundances of the associations observed. However, the stars HD 12993, HD 242908, and HD 193595 may be blue stragglers with moderately enhanced helium abundance (He/H ~ 0.19).</p>
<p>Relative carbon abundances have been determined empirically by comparison of the CIV 5812Å and HeII 4542Å equivalent widths. It is found that the association Cyg 0B2 is overabundant in carbon by ~50%. Likewise, the blue straggler HD 236894 is underabundant in carbon by a factor of two.</p>
<p>The estimated effective temperatures of the sample are compared to the previously accepted calibration of MK spectral types to the effective temperature. Estimates of the radii and masses of the stars in the sample have been calculated from their physical parameters and their absolute visual magnitudes.</p>https://thesis.library.caltech.edu/id/eprint/2578Quantum optics with cold atoms--nonlinear spectroscopy and road toward single-atom trap
https://resolver.caltech.edu/CaltechETD:etd-10112007-092812
Authors: {'items': [{'id': 'Hu-Z', 'name': {'family': 'Hu', 'given': 'Zhen'}, 'show_email': 'NO'}]}
Year: 1995
DOI: 10.7907/ykpq-pa09
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Investigations of optical processes for laser cooled and trapped atoms are described. Fluorescence from Cs atoms in a magneto-optical trap is detected under conditions of very low atomic density. Discrete steps are observed in the fluorescent signal versus time and are associated with the arrival and departure of individual trapped atoms. Histograms of the frequency of occurrence of a given level of fluorescence exhibit a series of uniformly spaced peaks that are attributed to the presence of N = 0, 1, 2 atoms in the trap.
In addition, numerical absorption and emission spectra for three-level [...], [...], and V systems under intense radiations are calculated. Absorption spectra for a [...] system is used to explain the probe-wave amplification and absorption spectra recorded for Cs atoms cooled and confined in a magneto-optical trap, in which novel spectral features of narrow frequency widths with single-pass gain exceeding 20% are observed. The consequence of the optical gain is demonstrated to lead to negative radiation pressure, which is investigated together with other mechanical forces in the trap. Various alternative trapping schemes in three-level and two-level atoms are proposed
as possible means to compress an atomic sample and demonstrated for a two-level magneto-optical trap.
https://thesis.library.caltech.edu/id/eprint/4038Dynamics of Amplitude and Phase in Semiconductor Lasers and Effects of Propagation in Dispersive Optical Fibers
https://resolver.caltech.edu/CaltechETD:etd-06072005-131657
Authors: {'items': [{'email': 'wkm@epilimnion.com', 'id': 'Marshall-William-K', 'name': {'family': 'Marshall', 'given': 'William K.'}, 'show_email': 'NO'}]}
Year: 1997
DOI: 10.7907/amwv-x166
<p>The work described in this thesis occupies the region of overlap between the modulation, chirp, and noise properties of semiconductor lasers on one hand and dispersive propagation in optical fiber on the other. It is shown herein that simple relationships exist between the amplitude and phase variations of different kinds and that these relations lead to consequences of dispersive propagation which are different for the noise from semiconductor lasers than for the modulation. A range of topics related to the main theme of the interplay between laser chirp, amplitude-phase correlation, and dispersive propagation is considered. That there is much to be gained by understanding them together, as inter-related issues, is the overall conclusion.</p>
<p>First, changes in intensity variations which occur during dispersive propagation are described compactly in terms of a transfer function involving the relationship between amplitude and phase variations of the source. Then, the main dynamic characteristics of semiconductor lasers are described including the relationships between amplitude and phase variations produced by modulation and noise in semiconductor lasers. For an appropriate combination of laser and fiber parameters, it is demonstrated that the laser intensity noise can be reduced over a wide range of frequencies. It is also demonstrated that the change in relative intensity noise with propagation has a different dependence on laser and fiber parameters than does the change in modulation response. Next, the phenomenon of adiabatic compression of the gain and index of refraction in a semiconductor due to spectral hole burning is considered, clarifying some aspects of the commonly-used spectral hole burning model. Finally, the problem of the semiconductor laser and dispersive propagation of the output is re-examined within a quantum mechanical context and the input-output relations for the laser are explored.</p>https://thesis.library.caltech.edu/id/eprint/5224Signal Extraction and Optical Design for an Advanced Gravitational Wave Interferometer
https://resolver.caltech.edu/CaltechTHESIS:04302012-152752095
Authors: {'items': [{'id': 'Mason-James-Edward', 'name': {'family': 'Mason', 'given': 'James Edward'}, 'show_email': 'NO'}]}
Year: 2001
DOI: 10.7907/amrv-a028
<p>The LIGO project is two 4 km baseline interferometers which are currently being
constructed in the quest to directly detect gravitational radiation. Concurrent with
this effort is research aimed at increasing the strain sensitivity of the initial interferometers to 2.5 x 10^(-23)/√Hz. The optical configuration, which defines the detector gain and bandwidth, is one such area of research. Resonant sideband extraction (RSE) is the configuration which is proposed for advanced LIGO. RSE allows for much more freedom in the optimization of the detector response compared to the
initial configuration.</p>
<p>The principle of RSE is examined in the context of a three mirror coupled cavity.
The effect of optical losses on the design of an RSE interferometer is discussed. Two
model optimizations of the interferometer design are done: one for binary inspiral
sources and one for periodic sources at 1 kHz.</p>
<p>An optical heterodyne signal extraction scheme is proposed to sense the deviation
of the mirrors away from their nominal positions, and to read out the gravitational
wave signal. The scheme is applied to the two model interferometers previously
designed, and its performance is analyzed for each case. Allowable residual deviations of the common mode degrees of freedom are also derived.</p>
<p>A tabletop prototype of an RSE interferometer has been constructed to demonstrate
both the viability of the proposed signal extraction scheme and the tunability
of the RSE interferometer. Good agreement on both counts is found between the
measured experimental data and the modeled predictions.</p>
<p>The coupling of laser frequency and amplitude noise into the gravitational wave
readout port is analyzed for the RSE configuration assuming the proposed gravitational
wave signal readout scheme. Specifications for the allowable laser frequency
and amplitude noise, as well as allowable residual deviations of the differential mode
degrees of freedom, are derived for the two model interferometers.</p>
https://thesis.library.caltech.edu/id/eprint/6994Synthesis, Passivation and Charging of Silicon Nanocrystals
https://resolver.caltech.edu/CaltechETD:etd-01132002-032219
Authors: {'items': [{'email': 'eboer@alumni.caltech.edu', 'id': 'Boer-Elizabeth-A', 'name': {'family': 'Boer', 'given': 'Elizabeth A.'}, 'show_email': 'YES'}]}
Year: 2001
DOI: 10.7907/ZB66-SN79
<p>Silicon nanocrystals are intriguing from both a fundamental and an applied physics point of view. The efficient room temperature luminescence exhibited by Si nanocrystals (as compared to bulk silicon) and the apparent size-dependent bandgap of Si nanocrystals are two incompletely explained phenomena. Meanwhile, the applied physicist may take advantage of the optical and electronic properties of small Si structures to build devices not possible with only bulk silicon.</p>
<p>In this thesis, nanocrystal samples produced by aerosol techniques were investigated. The aerosol samples were size-classified in the size range of 2-50 nm with a size variation of 15-20%. Conducting tip atomic force microscopy (AFM) was used to manipulate and investigate the samples' charging characteristics. The AFM was used to inject charge into single Si nanocrystals and to observe the dissipation.</p>
<p>The charging characteristics of samples made by ion implantation and annealing were also explored. An atomic force microscope was used to locally inject, detect and quantify the amount and location of charge in SiO2 films containing Si nanocrystals (size 2-6 nm). By comparison with control samples, charge trapping was shown to be due to nanocrystals and not ion implantation-induced defects in these samples.</p>
<p>Two models were developed for quantitative charge imaging with an atomic force microscope, one appropriate for non-contact mode and the other for intermittent contact (tapping) mode imaging. From the models, estimates of the best charge sensitivity of an unbiased standard AFM cantilever were found to be on the order of a few electrons. The models were used to estimate the amount of charge injected in the charging experiments: in typical experiments, on the order of 60 electrons were injected in an isolated Si nanoparticle, and a few hundred electrons were injected in SiO2 films containing Si nanocrystals.</p>
<p>Finally, for optical studies, nanocrystal passivation with hydrogen and SiO2 were briefly investigated using photoluminescence and X-ray photoelectron spectroscopy.</p>https://thesis.library.caltech.edu/id/eprint/145Analysis of Neuronal Dynamics in Behaving Animals
https://resolver.caltech.edu/CaltechTHESIS:01262012-143944303
Authors: {'items': [{'id': 'Pesaran-Bijan', 'name': {'family': 'Pesaran', 'given': 'Bijan'}, 'show_email': 'NO'}]}
Year: 2002
DOI: 10.7907/JQV4-Z245
This thesis presents a set of mathematical techniques for analyzing neural activity and then applies them to data from a variety of experiments. Imaging data, in which movies of brain activity are recorded, is considered first and ways to suppress noise and characterize the signal are explored. Data from the cortex of behaving monkeys is then considered. These techniques are used to analyze the activity of populations of neurons during eye movements. Oscillations are found that encode information predicting "where" and "when" an eye movement is made. Activity in other parts of the brain involved in reaching and the perception of motion are then analyzed and shown to encode other information in a similar way. These results show neuronal dynamics may be used by the brain to process information during behavior.https://thesis.library.caltech.edu/id/eprint/6785Lock Acquisition in Resonant Optical Interferometers
https://resolver.caltech.edu/CaltechETD:etd-12062004-115632
Authors: {'items': [{'email': 'mevans@ligo.caltech.edu', 'id': 'Evans-Matthew-John', 'name': {'family': 'Evans', 'given': 'Matthew John'}, 'show_email': 'NO'}]}
Year: 2002
DOI: 10.7907/N1J2-M098
The LIGO (Laser Interferometric Gravitational-wave Observatory) project, and other projects around the world, are currently planning to use long-baseline (> 1 km) interferometers to directly detect gravitational radiation from astrophysical sources. In this work we present a framework for lock acquisition, the process by which an initially uncontrolled resonant interferometer is brought to its operating point. Our approach begins with the identification of a path which takes the detector from the uncontrolled state to the operational state. The properties of the detector's outputs along this path, embodied in the sensing matrix, must be determined and parameterized in terms of measureables. Finally, a control system which can compute the inverse of the sensing matrix, apply it to the incoming signals, and make the resulting signals available for feedback is needed to close the control loop. This formalism was developed and explored extensively in simulation and was subsequently applied to the LIGO interferometers. Results were in agreement with expectation within error, typically ±20% on the sensing matrix elements, and the method proved capable of bringing a high-finesse power-recycled Fabry-Perot-Michelson interferometer (a LIGO detector) to its operating point.https://thesis.library.caltech.edu/id/eprint/4806Modeling and Detecting Gravitational Waves from Compact Stellar Objects
https://resolver.caltech.edu/CaltechETD:etd-05292002-113750
Authors: {'items': [{'email': 'vallis@vallis.org', 'id': 'Vallisneri-Michele', 'name': {'family': 'Vallisneri', 'given': 'Michele'}, 'orcid': '0000-0002-4162-0033', 'show_email': 'NO'}]}
Year: 2002
DOI: 10.7907/JN6M-BW40
<p>In the next few years, the first detections of gravity-wave signals using Earth-based interferometric detectors will begin to provide precious new information about the structure, dynamics, and evolution of compact bodies, such as neutron stars and black holes, both isolated and in binary systems. The intrinsic weakness of gravity-wave signals requires a proactive approach to modeling the prospective sources and anticipating the shape of the signals that we seek to detect. Full-blown 3-D numerical simulations of the sources are playing and will play an important role in planning the gravity-wave data-analysis effort. This thesis explores the interplay between numerical source modeling and data analysis, looking closely at three case studies.</p>
<p>1. I evaluate the prospects for extracting equation-of-state information from neutron-star tidal disruption in neutron-star–black-hole binaries with LIGO-II, and I estimate that the observation of disrupting systems at distances that yield about one event per year should allow the determination of the neutron-star radius to about 15%, which compares favorably to the currently available electromagnetic determinations.</p>
<p>2. In collaboration with Lee Lindblom and Joel Tohline, I perform numerical simulations of the nonlinear dynamics of the <i>r</i>-mode instability in young, rapidly spinning neutron stars, and I find evidence that nonlinear couplings to other modes will not pose a significant limitation to the growth of the <i>r</i>-mode amplitude.</p>
<p>3. In collaboration with Alessandra Buonanno and Yanbei Chen, I study the problem of detecting gravity waves from solar-mass black-hole–black-hole binaries with LIGO-I, and I construct two families of <i>detection</i> templates that address the inadequacy of standard post-Newtonian theory to predict reliable waveforms for these systems.</p>
https://thesis.library.caltech.edu/id/eprint/2226Pulsar Searches: From Radio to Gamma-Rays
https://resolver.caltech.edu/CaltechETD:etd-01232003-213508
Authors: {'items': [{'id': 'Chandler-Adam-Matthew', 'name': {'family': 'Chandler', 'given': 'Adam Matthew'}, 'show_email': 'NO'}]}
Year: 2003
DOI: 10.7907/MDJX-M255
<p>We report the results of four different pulsar searches, covering radio, X-ray, and gamma-ray wavelengths. These searches targeted pulsars in virtually all of their guises: young and old, long-period and short-period, accretion-powered and rotation-powered. Ten new pulsars were discovered.</p>
<p>There are very few known gamma-ray pulsars, all of which were found by folding gamma-ray data with a pulse period known from other wavelengths. Some emission models indicate that there may be a large number of gamma-ray pulsars that are undetectable at lower energies. We searched several of the brightest unidentified gamma-ray sources for pulsations. This was the first attempt to identify gamma-ray pulsars by a direct search of gamma-ray data. No new identifications resulted and we report upper limits.</p>
<p>Even more rare than gamma-ray pulsars are accreting millisecond pulsars. We searched for coherent pulsations from Aql X-1, a low-mass X-ray binary suspected of harboring such an object. No pulsations were detected, and we argue that the quiescent emission of this system has a thermal origin (i.e., it is not due to low-level accretion).</p>
<p>The two radio searches included here were both designed to detect millisecond pulsars. First, we report the results of a large area survey from Arecibo. Five new slow pulsars were discovered, including an apparent orthogonal rotator and an extremely unusual bursting radio pulsar. No short-period pulsars were discovered and we place some of the first useful observational constraints on the limiting spin period of a neutron star.</p>
<p>We also performed pointed searches of several globular clusters using the new Green Bank Telescope. Three new binary millisecond pulsars were found in M62. These were the first new objects found with the GBT, and they bring the total pulsar population in M62 to six. We also discovered two isolated pulsars, one each in NGC 6544 and NGC 6624.</p>
<p>Many of the methods we developed will be relevant to future searches. Perhaps the most significant contribution is a dynamic power spectrum-based technique that finally allows sensitive searches for binary pulsars whose orbital periods are of the same order as the observation time.</p>https://thesis.library.caltech.edu/id/eprint/286Mirror Thermal Noise in Interferometric Gravitational Wave Detectors
https://resolver.caltech.edu/CaltechETD:etd-05092003-153759
Authors: {'items': [{'id': 'Rao-Shanti-Raja', 'name': {'family': 'Rao', 'given': 'Shanti Raja'}, 'show_email': 'NO'}]}
Year: 2003
DOI: 10.7907/5W0V-QB90
<p>The LIGO (Laser Interferometer Gravitational-wave Observatory) project has begun its search for gravitational waves, and efforts are being made to improve its ability to detect these. The LIGO observatories are long, Fabry-Perot-Michelson interferometers, where the interferometer mirrors are also the gravitational wave test masses. LIGO is designed to detect the ripples in spacetime caused by cataclysmic astrophysical events, with a target gravitational wave minimum strain sensitivity of 4 x 10^-22 around 100 Hz. The Advanced LIGO concept calls for an order of magnitude improvement in strain sensitivity, with a better signal to noise ratio to increase the rate of detection of events. Some of Advanced LIGO's major requirements are improvements over the LIGO design for thermal noise in the test mass substrates and reflective coatings.</p>
<p>Thermal noise in the interferometer mirrors is a significant challenge in LIGO's development. This thesis reviews the theory of test mass thermal noise and reports on several experiments conducted to understand this theory.v
<p>Experiments to measure the thermal expansion of mirror substrates and coatings use the photothermal effect in a cross-polarized Fabry-Perot interferometer, with displacement sensitivity of 10^-15 m/rHz. Data are presented from 10 Hz to 4kHz on solid aluminum, and on sapphire, BK7, and fused silica, with and without commercial TiO2/SiO2 dielectric mirror coatings. The substrate contribution to thermal expansion is compared to theories by Cerdonio et al. and Braginsky, Vyatchanin, and Gorodetsky. New theoretical models are presented for estimating the coating contribution to the thermal expansion. These results can also provide insight into how heat flows between coatings and substrates relevant to predicting coating thermoelastic noise.</p>
<p>The Thermal Noise Interferometer (TNI) project is a interferometer built specifically to study thermal noise, and this thesis describes its construction and commissioning. Using LIGO-like designs, components, and processes, the TNI has a minimum length noise in each of two arm cavities of 5 x 10^-18 m/rHz around 1 kHz.</p>https://thesis.library.caltech.edu/id/eprint/1696Topics of LIGO Physics: Quantum Noise in Advanced Interferometers and Template Banks for Compact-Binary Inspirals
https://resolver.caltech.edu/CaltechETD:etd-05302003-044325
Authors: {'items': [{'email': 'yanbei@tapir.caltech.edu', 'id': 'Chen-Yanbei', 'name': {'family': 'Chen', 'given': 'Yanbei'}, 'orcid': '0000-0002-9730-9463', 'show_email': 'NO'}]}
Year: 2003
DOI: 10.7907/VQH0-QA78
This thesis deals with the planning for advanced interferometric gravitational-wave detectors, as well as the detection of inspiral waves using first-generation interferometers.
In Chapters 2 -- 4 (in collaboration with Alessandra Buonanno), the the signal recycling interferometer proposed for LIGO-II is studied in the two-photon formalism. This study reveals the optical spring effect, which allows the interferometer to beat the standard quantum limit, while in the same time introduces a dynamical instability. A classical control system is designed to suppress this instability. In Chapter 5 (in collaboration with Alessandra Buonanno and Nergis Mavalvala), the quantum noise in heterodyne readout schemes for advanced interferometers is studied. In Chapter 6 (in collaboration with Patricia Purdue), a QND Speed-Meter interferometer with Michelson topology is proposed, analyzed and shown to be a promising candidate for third-generation interferometers (LIGO-III or EURO). This design requires adding a kilometer-scale cavity into the interferometer. In Chapter 7, Sagnac interferometers are analyzed and shown to exhibit a similar broadband QND performance without the need of additional cavity --- as expected since these interferometers are sensitive only to time-dependent mirror displacement, and are automatic speed meters.
In Chapter 8 (in collaboration with Alessandra Buonanno and Michele Vallisneri), the Post-Newtonian (PN) breakdown at late-stage inspirals of non-spinning binary black holes is studied. We propose the use of Detection Template Families (DTFs) --- extensions of ordinary PN templates that can mimic all different PN waveforms and hence are plausible to catch the real waveform, yet do not provide straightforward parameter estimation. In Chapter 9 (in collaboration with Alessandra Buonanno and Michele Vallisneri), binaries carrying spins are studied using an adiabatic PN model. Based on features of the precession dynamics, we construct a DTF, using a modified Apostolatos' ansatz, that can mimic the modulated waveforms reasonably well, while keeping a small number of parameters to be searched over one by one, with the rest searched over automatically. We also propose a (computationally) plausible way of searching over the entire physical parameter space of neutron-star--black-hole binaries.https://thesis.library.caltech.edu/id/eprint/2286Cavity QED in Microsphere and Fabry-Perot Cavities
https://resolver.caltech.edu/CaltechETD:etd-05292003-214249
Authors: {'items': [{'email': 'josephrbuck@yahoo.com', 'id': 'Buck-Joseph- Robert', 'name': {'family': 'Buck', 'given': 'Joseph Robert'}, 'show_email': 'NO'}]}
Year: 2003
DOI: 10.7907/585P-6F46
<p>A long-standing ambition in the field of cavity quantum electrodynamics has been to trap single atoms inside high-Q cavities in a regime of strong coupling. Our goal has been to develop techniques for trapping that are compatible with strong coupling and that do not interfere with the cavity QED interactions. This is crucial for applications to quantum computation and communication. We have accomplished this goal by creating a trapping potential through an intracavity FORT at the 'magic' wavelength for Cesium, 935.6 nm. Unlike typical FORTs, where the signs of the AC-Stark shifts for excited and ground states are opposite, our trap causes small shifts to the relevant transition frequencies, enabling a trapping potential for the center-of-mass motion that is largely independent of the internal atomic state. This has enabled us to achieve extended trapping times (3 sec) for individual Cesium atoms in cavity QED in a regime of strong coupling. Although our longest lifetimes are obtained when the probing fields are turned off, the atoms can also be continuously monitored, leading to mean trapping times of 0.4 sec, with some atoms observed for over 1 sec.</p>
<p>An important tool for studying atom-field interactions is a high-Q cavity with small mode volume. Considerable effort has been made in advancing our capabilities for high-Q resonators. While much of our work involves Fabry-Perot cavities, some of the highest quality optical resonators to date have been achieved with the whispering gallery modes (WGMs) of quartz microspheres (Q = 8 x 10⁹). Therefore, considerable effort has been given to understanding the usefulness of microspheres for cavity QED with strong coupling. We have also worked at manufacturing high-Q microspheres suitable for cavity QED. To this end, we have been successful at making spheres with a radius of 10 microns and Q = 10⁷.</p>https://thesis.library.caltech.edu/id/eprint/2240Topics in Gravitational-Wave Astronomy
https://resolver.caltech.edu/CaltechETD:etd-08052003-161044
Authors: {'items': [{'email': 'richard.oshaughnessy@ligo.org', 'id': "O'Shaughnessy-Richard-William", 'name': {'family': "O'Shaughnessy", 'given': 'Richard William'}, 'orcid': '0000-0001-5832-8517', 'show_email': 'YES'}]}
Year: 2004
DOI: 10.7907/4C1K-VZ17
<p>Both the Laser Interferometer Gravitational Wave Observatory (LIGO) and the Laser Interferometer Space Antenna (LISA) will over the next decade detect gravitational waves emitted by the motion of compact objects (e.g. black hole and neutron star binaries). This thesis presents methods to improve (i) LIGO detector quality, (ii) our knowledge of waveforms for certain LIGO and LISA sources, and (iii) models for the rate of detectability of a particular LISA source.</p>
<p>1) Plunge of compact object into a supermassive black hole: LISA should detect many inspirals of compact objects into supermassive black holes (~ 10⁵-10⁷ M<sub>⊙</sub>). Since the inspiral of each compact object terminates shortly after the inspiralling object reaches its last stable orbit, the late-stage inspiral waveform provides insight into the location of the last stable orbit and strong-field relativity. I discovered that while LISA will easily see the overall inspiral (consisting of many cycles before plunge), the present LISA design will just miss detecting the waves emitted from the transition from inspiral to plunge.</p>
<p>2) Scheme to reduce thermoelastic noise in advanced LIGO: After its first upgrade, LIGO will have its sensitivity limited by thermoelastic noise. [Thermoelastic noise occurs because milimeter-scale thermal fluctuations in the mirror bulk expand and contract, causing the mirror surface to shimmer.] The interferometer's sensitivity could be enhanced substantially by reducing thermoelastic noise. In collaboration with Kip Thorne, Erika d'Ambrosio, Sergey Vyatchanin, and Sergey Strigin, I developed a proposal to reduce thermoelastic noise in advanced-LIGO by switching the LIGO cavity optics from simple spherical mirrors to a new, Mexican-hat shape.</p>
<p>3) Geometric-optics-based analysis of stability of symmetric-hyperbolic formulations of Einstein's equations: Einstein's equations must be evolved numerically to predict accurate waveforms for the late stages of binary black hole inspiral and merger. But no matter which representation of Einstein's equations is used, numerical simulations rarely run long. For examle, for first-order symmetric-hyperbolic (FOSH) formulations of Einstein's evolution equations, sometimes exact but unphysical solutions grow so large that the evolution fails. For FOSH formulations, I found easily-understood solutions (wave packets) and used them to predict which formulations will be particularly ill-behaved.</p>https://thesis.library.caltech.edu/id/eprint/3017Spatiotemporal Chaos in Rayleigh-Bénard Convection
https://resolver.caltech.edu/CaltechETD:etd-08062003-162208
Authors: {'items': [{'email': 'ChiamKH@MailAPS.ORG', 'id': 'Chiam-Keng-Hwee', 'name': {'family': 'Chiam', 'given': 'Keng-Hwee'}, 'orcid': '0000-0002-8987-8463', 'show_email': 'YES'}]}
Year: 2004
DOI: 10.7907/2NJV-BB91
<p>Spatiotemporal chaos, or disorder in both the space and time coordinates, is studied in direct numerical simulations of Rayleigh-Bénard convection. In particular, the following investigations pertaining to spiral defect chaos are discussed.</p>
<p>First, in the absence of the mean flow, spiral defect chaos is found to collapse to a stationary pattern comprising textures of stripes with angular bends. The quenched patterns are characterized by mean wave numbers that approach those uniquely selected by focus-type singularities, which, in the absence of the mean flow, lie at the zig zag instability boundary. In addition, mean flow is shown to contribute to the phenomenon of rolls terminating perpendicularly into lateral walls. In the absence of the mean flow, rolls begin to terminate into lateral walls at an oblique angle. This obliqueness increases with the Rayleigh number.</p>
<p>Second, the transport of passive tracers in the presence of advection by spiral defect chaos is found to be characterized by normal diffusion. The enhancement in the tracer diffusivity follows two regimes. When the molecular diffusivity of the tracer concentration is small, the enhancement is proportional to the Péclet number. When the molecular diffusivity is large, the enhancement is proportional to the square root of the Péclet number. This difference is explained in terms of the dependence of the transport on the local wave numbers. It is found that tracer concentrations with small molecular diffusivity experience enhanced longitudinal diffusion and suppressed lateral diffusion at regions of the flow occupied by defects.</p>
<p>Third, perturbations in spiral defect chaos are found to propagate in a localized manner. In particular, they nucleate around the defect structures in the flow. In addition, an oscillatory instability at the spiral core is discovered. Finally, the propagation in pre-chaotic stripe textures is explained in terms of the diffusion of the phase variable of the stripe state.</p>https://thesis.library.caltech.edu/id/eprint/3020Ionic Charge States of Solar Energetic Particles
https://resolver.caltech.edu/CaltechETD:etd-09122003-110331
Authors: {'items': [{'email': 'lsollitt@psi.edu', 'id': 'Sollitt-Luke', 'name': {'family': 'Sollitt', 'given': 'Luke'}, 'show_email': 'YES'}]}
Year: 2004
DOI: 10.7907/G8XC-XY96
<p>A novel technique to infer average ionic charge states of high energy (≥ 10 MeV/nuc) solar energetic particles (SEPs) in large solar events is presented. In some large SEP events, it is observed that higher energy SEPs decay in intensity more rapidly than at lower energies. Furthermore, this energy dependence varies with particle species, as would be expected if the decay timescale depended on a rigidity-dependent diffusive mean free path. Observations are done with the Solar Isotope Spectrometer (SIS) on board the Advanced Composition Explorer spacecraft. By comparing the decay timescales of nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron to a reference element, such as carbon, charge states are inferred for these elements in three SEP events between 1997 and 2002. In a fourth event, upper limits of charge states are inferred. For the solar event of November 6, 1997, charge states are also inferred for sodium, calcium, and nickel. These charge states are compared with other measurements at similar energies, and with measurements at lower energies.</p>
<p>Two interpretations of the data are discussed. First, if there is no stripping in the shock acceleration process, the charge states inferred for the events might be indicative of source plasma temperatures (Arnaud and Rothenflug, 1985; Arnaud and Raymond, 1992). It is found that two of the events examined have temperatures consistent with the acceleration of particles from the corona. The other two events have best fit temperatures that might indicate a mixture of sources, including the corona and a hot flare region. Second, iron charge states from this work and from other work (Mazur et al., 1999; Mobius et al., 1999; Cohen et al., 1999) at various energies for the November 6, 1997, event are compared to the models of Barghouty and Mewaldt (2000) and Kovaltsov et al. (2001) for shock acceleration in a dense plasma, which include the effects of stripping and recombination due to interactions with protons and electrons. These models can describe the observed charge state spectra with acceleration from the corona without invoking mixture with a hot source.</p>https://thesis.library.caltech.edu/id/eprint/3493Trapped Atoms in Cavity QED for Quantum Optics and Quantum Information
https://resolver.caltech.edu/CaltechETD:etd-06032004-163753
Authors: {'items': [{'id': 'McKeever-Jason-Terence-Taylor', 'name': {'family': 'McKeever', 'given': 'Jason Terence Taylor'}, 'show_email': 'NO'}]}
Year: 2004
DOI: 10.7907/8DSY-DF56
<p>One of the requirements for the physical implementation of many protocols in quantum information science is the ability to convert quantum information from stationary to travelling form and transmit it over long distances. The strong coupling domain of cavity quantum electrodynamics (QED) provides a near-ideal setting for the pursuit of these goals. In addition, cavity QED is a unique system for the study of open quantum systems and quantum coherence. Cavity QED experiments have entered a new era in recent years, with the advent of single atom intracavity trapping.</p>
<p>Experiments described in this thesis represent significant progress in these areas. Beginning with a tremendous set of improvements to far-off-resonance optical trapping of single Cs atoms in a Fabry-Perot resonator, we have undertaken a series of investigations in which strongly coupled trapped atoms have been used for quantum optics and quantum information. These improvements in trapping go beyond quantitative lengthening of storage times, in that the trap is largely insensitive to the atom's internal state.</p>
<p>As a result of this unique property of the optical trap, a breakthrough was made in the continuous observation time of trapped atoms. Individual atoms can be observed for times of order 1 second, and this scheme enables real-time monitoring and measurement of the number of atoms strongly coupled to the cavity. This enables deterministic preparation of a particular atom number of the experimenter's choice.</p>
<p>Using single trapped atoms in our cavity, we have also experimentally realized the one-atom laser in a regime of strong coupling. The unconventional characteristics of this system are explored in detail, including strongly nonclassical output. This represents a significant milestone of long-standing interest in the quantum optics community, and goes beyond previous work with atomic beams where there was a fluctuating atom number in the cavity.</p>
<p>Finally, we have achieved the first deterministic generation of single photons in a setting suitable for quantum networks. By illuminating a strongly coupled, trapped atom by classical laser pulses, single photons have been generated on demand, with intrinsic efficiency near unity. Although a great deal of work remains to configure this system as a true node in a quantum network, the ground-work has been laid for progress in the near future, where one goal is to create an entangled state of two atoms in distantly separated cavities.</p>https://thesis.library.caltech.edu/id/eprint/2421Resonant Excitation of White Dwarf Oscillations in Compact Object Binaries
https://resolver.caltech.edu/CaltechETD:etd-05272005-160411
Authors: {'items': [{'id': 'Rathore-Yasser', 'name': {'family': 'Rathore', 'given': 'Yasser'}, 'show_email': 'NO'}]}
Year: 2005
DOI: 10.7907/0726-4X92
<p>White dwarfs are ubiquitous in the known Universe. They are frequently found in binary systems with ordinary stars, giants, or compact objects as companions. Depending upon their histories, such systems may have significantly eccentric orbits. Because of gravitational radiation, a white dwarf-compact object binary will shrink and circularize with time. If the system is initially close enough, then the inspiral will occur on a time-scale shorter than a Hubble time. As an eccentric system inspirals, it will pass through resonances when harmonics of the orbital period match one of the white dwarf's normal mode eigenfrequencies. At these tidal resonances, energy can be transferred from the orbit to the white dwarf normal modes, and the system will pass through a sequence of such resonances for each mode. If the amplitude of a mode is driven high enough, the modes may damp due to non-linear processes and heat the white dwarf. If the temperature of the white dwarf can be raised in this way to a critical value, then the star may undergo a thermonuclear detonation that results in a Type Ia supernova. In order to determine whether such a scenario is possible, and what other observable consequences of tidal resonances may be, it is necessary to understand the resonant energy transfer and the non-linear evolution of modes on a white dwarf in some detail.</p>
<p>A variational approach to the excitation of dynamical tides is presented. This is then used to study the energy transfer in the resonant excitation of tides. The energy transfer problem is complicated by the fact that a mode perturbs the orbit as it is resonantly excited, effectively creating a non-linear feedback loop. We call this effect 'back reaction.' In the present work, the problem is considered both in the approximation when back reaction is neglected, and when it is included. It is found that back reaction changes the resonant energy transfer both qualitatively and quantitatively. In particular, unlike the no back reaction case, the energy transfer with back reaction is shown to be always positive to lowest order in the rate of dissipation by gravitational radiation, and any initial energy in the mode before resonance is shown to increase the energy transfer.</p>
<p>Numerical simulations of resonant mode excitation and non-linear evolution of white dwarf oscillations are also considered. An adiabatic, parallel hydrodynamic code is described for this. Results from several test problems and preliminary simulations of resonant tidal excitation are presented.</p>
<p>The formalism developed for resonant tidal excitation is applied to studying the feasibility of a tidally triggered supernova via resonant excitation of quadrupolar f-modes. It is found that a 1.4 solar mass companion to the white dwarf is not viable, which rules out double degenerates and white dwarf-neutron star binaries as potential progenitors. However, it is found that with a companion mass of ten to hundred thousand solar masses, there exist regions in the parameter space where the white dwarf can be detonated before tidal disruption. It is calculated that the ejecta from such a detonation would remain trapped in orbit around the companion for the majority of cases, and would presumably be accreted eventually.</p>
<p>A preliminary calculation of the importance of tidal effects for gravitational wave observations of capture sources with central masses of about a million solar masses is also presented. The resonant excitation of f-modes is found to be unimportant because of the long orbital periods at the last stable orbits. It is, however, found that the excitation of g-modes could introduce significant errors in the parameter estimation for such systems, though it would probably not affect detection capability. The exact magnitude of the errors depends upon the density of resonances during the period of observation, and therefore depends upon details of the white dwarf model.</p>https://thesis.library.caltech.edu/id/eprint/2159Cavity QED with Multilevel Atoms
https://resolver.caltech.edu/CaltechETD:etd-05272005-103306
Authors: {'items': [{'id': 'Birnbaum-Kevin-Michael', 'name': {'family': 'Birnbaum', 'given': 'Kevin Michael'}, 'show_email': 'NO'}]}
Year: 2005
DOI: 10.7907/H7ZS-W151
<p>The steady-state transmission spectrum of a cavity with two modes of orthogonal polarization strongly coupled to a single atom with multiple Zeeman states is computed. Effects due to cavity birefringence and atomic ac-Stark shifts are included. The transmission spectrum is compared to experimental results for a single Cesium atom trapped via an intracavity FORT in a Fabry-Perot cavity. The excellent agreement of the theory with the data is used to infer the distribution of the position of the trapped atom.</p>
<p>The intensity correlation function of this system is also calculated, and found to be strongly antibunched and sub-Poissonian. This effect is explained in terms of photon blockade, based on the structure of the lowest energy eigenvalues. Experimental results confirm the strong nonlinearity at the single-photon level.</p>
<p>We present theoretical predictions of the weak field spectra of microtoroid and photonic bandgap cavities strongly coupled to the D2 transition of single Cesium atoms. These calculations include all hyperfine and Zeeman states of the transition and model the cavity as a single-mode, linearly polarized resonator.</p>
<p>Finally, we outline a technique for using multiple hyperfine and Zeeman levels of a single atom in a strongly coupled atom-cavity system to generate polarized single photons on demand in a well-defined temporal mode via adiabatic passage. The technique is insensitive to cavity birefringence and only weakly sensitive to atomic position. Variations of this technique for generating entanglement of photon polarization and atomic Zeeman state are also discussed.</p>https://thesis.library.caltech.edu/id/eprint/2144All-Optical Spinor Bose-Einstein Condensation and the Spinor Dynamics-Driven Atom Laser
https://resolver.caltech.edu/CaltechETD:etd-05242006-104400
Authors: {'items': [{'email': 'lundblad@gmail.com', 'id': 'Lundblad-Nathan-Eric', 'name': {'family': 'Lundblad', 'given': 'Nathan Eric'}, 'orcid': '0000-0003-0430-8064', 'show_email': 'YES'}]}
Year: 2006
DOI: 10.7907/WEVF-9991
<p>Optical trapping as a viable means of exploring the physics of ultracold dilute atomic gases has revealed a new spectrum of physical phenomena. In particular, macroscopic and sudden occupation of the ground state below a critical temperature—-a phenomenon known as Bose-Einstein condensation—-has become an even richer system for the study of quantum mechanics, ultracold collisions, and many-body physics in general. Optical trapping liberates the spin degree of the BEC, making the order parameter vectorial (‘spinor BEC’), as opposed to the scalar order of traditional magnetically trapped condensates.</p>
<p>The work described within is divided into two main efforts. The first encompasses the all-optical creation of a Bose-Einstein condensate in rubidium vapor. An all-optical path to spinor BEC (as opposed to transfer to an optical trap from a magnetic-trap condensate) was desired both for the simplicity of the experimental setup and also for the potential gains in speed of creation; evaporative cooling, the only known path to dilute-gas condensation, works only as efficiently as the rate of elastic collisions in the gas, a rate that starts out much higher in optical traps. The first all-optical BEC was formed elsewhere in 2001; the years following saw many groups worldwide seeking to create their own version. Our own all-optical spinor BEC, made with a single-beam dipole trap formed by a focused CO₂ laser, is described here, with particular attention paid to trap loading, measurement of trap parameters, and the use of a novel 780 nm high-power laser system.</p>
<p>The second part describes initial experiments performed with the nascent condensate. The spinor properties of the condensate are documented, and a measurement is made of the density-dependent rate of spin mixing in the condensate. In addition, we demonstrate a novel dual-beam atom laser formed by outcoupling oppositely polarized components of the condensate, whose populations have been coherently evolved through spin dynamics. We drive coherent spin-mixing evolution through adiabatic compression of the initially weak trap. Such dual beams, nominally number-correlated through the angular momentum-conserving collision m=0 + m=0 ⇌ m=+1 + m=-1 have been proposed as tools to explore entanglement and squeezing in Bose-Einstein condensates.</p>https://thesis.library.caltech.edu/id/eprint/2009Magnetic Microtraps for Cavity QED, Bose-Einstein Condensates, and Atom Optics
https://resolver.caltech.edu/CaltechETD:etd-09202005-205733
Authors: {'items': [{'email': 'benlev@stanford.edu', 'id': 'Lev-Benjamin-Leonard', 'name': {'family': 'Lev', 'given': 'Benjamin Leonard'}, 'show_email': 'YES'}]}
Year: 2006
DOI: 10.7907/YP00-7Z87
<p>The system comprised of an atom strongly coupled to photons, known as cavity quantum electrodynamics (QED), provides a rich experimental setting for quantum information processing, both in the implementation of quantum logic gates and in the development of quantum networks. Moreover, studies of cavity QED will help elucidate the dynamics of continuously observed open quantum systems with quantum-limited feedback.</p>
<p>To achieve these goals in cavity QED, a neutral atom must be tightly confined inside a high-finesse cavity with small mode volume for long periods of time. Microfabricated wires on a substrate---known as an atom chip---can create a sufficiently high-curvature magnetic potential to trap atoms in the Lamb-Dicke regime. We have recently integrated an optical fiber Fabry-Perot cavity with such a device. The microwires allow the on-chip collection and laser cooling of neutral atoms, and allow the magnetic waveguiding of these atoms to an Ioffe trap inside the cavity mode. Magnetically trapped intracavity atoms have been detected with this cavity QED system. A similar experiment employing microdisks and photonic bandgap cavities is nearing completion. With these more exotic cavities, a robust and scalable atom-cavity chip system will deeply probe the strong coupling regime of cavity QED with magnetically trapped atoms.</p>
<p>Atom chips have found great success in producing and manipulating Bose-Einstein condensates and in creating novel atom optical elements. An on-chip BEC has been attained in a miniaturized system incorporating an atom chip designed for atom interferometry and for studies of Josephson effects of a BEC in a double-well potential.</p>
<p>Using similar microfabrication techniques, we created and demonstrated a specular magnetic atom mirror formed from a standard computer hard drive. This device, in conjunction with micron-sized charged circular pads, can produce a 1-D ring trap which may prove useful for studying Tonks gases in a ring geometry and for creating devices such as a SQUID-like system for neutral atoms.</p>
<p>This thesis describes the fabrication and employment of these atoms chips in experiments at both Caltech and Munich, the latter in collaboration with Professors Theodore Haensch and Jakob Reichel at the Max Planck Institute for Quantum Optics.</p>https://thesis.library.caltech.edu/id/eprint/3658Rotating Rayleigh-Bénard Convection
https://resolver.caltech.edu/CaltechETD:etd-08252006-154116
Authors: {'items': [{'email': 'jscheel@oxy.edu', 'id': 'Scheel-Janet-D', 'name': {'family': 'Scheel', 'given': 'Janet D.'}, 'orcid': '0000-0002-1669-4188', 'show_email': 'YES'}]}
Year: 2007
DOI: 10.7907/961N-6776
<p>Rotating Rayleigh-Benard convection (rRBC) is studied as a paradigmatic example of pattern formation and spatiotemporal chaos. For large enough rotation rates, this system undergoes a supercritical bifurcation from the uniform state to a state known as domain chaos.</p>
<p>In domain chaos, domains of straight parallel rolls change their orientation and size discretely. This roll switching causes an overall counterclockwise precession of the pattern. An additional mechanism of precession, glide-induced precession, is introduced here, by deriving the rRBC amplitude equation to higher order. New terms due to the rotation cause rolls to precess whenever there is an amplitude gradient in the direction parallel to the rolls. Hence, dislocations which are stationary in a nonrotating system will glide in a rotating frame, causing the overall precession.</p>
<p>Theory that includes the Coriolis force but ignores the centrifugal force predicted scaling laws near the transition to domain chaos. However, experimenters found different scaling laws. The scaling laws are studied here by direct numerical simulations (DNS) for the exact parameters as experiments. When only the Coriolis force is included, the DNS scaling laws agree with theory. When the centrifugal force is also included, the DNS scaling laws agree better with experiment; hence the centrifugal force cannot be neglected from theory.</p>
<p>The coefficients of the amplitude equation for the Complex Ginzburg-Landau equation (CGLE) are found for DNS of traveling waves. They agree well with experimental results. The CGLE is chaotic for certain values of the coefficients. However, for the parameters in the DNS, those chaotic regimes were not realized.</p>
<p>Leading order Lyapunov exponents (LLE) and eigenvectors are computed for both rotating and nonrotating convection. For certain parameters, these systems are found to have positive LLEs; hence they are truly chaotic. For time-dependent systems, the leading eigenvector is characterized by localized bursts of activity which are associated with dynamical events. The short-time dynamics of the LLE is correlated with these dynamical events. However, contributions to the LLE are due to non-periodic events only.</p>
<p>Lagrangian particle tracking methods are employed for rRBC. These systems exhibit chaotic advection in that initially localized particle trajectories explore the available phase space.</p>https://thesis.library.caltech.edu/id/eprint/3217Topics in Gravitational-Wave Physics
https://resolver.caltech.edu/CaltechETD:etd-05232007-115433
Authors: {'items': [{'email': 'geoffrey4444@gmail.com', 'id': 'Lovelace-Geoffrey-Mark', 'name': {'family': 'Lovelace', 'given': 'Geoffrey Mark'}, 'orcid': '0000-0002-7084-1070', 'show_email': 'YES'}]}
Year: 2007
DOI: 10.7907/94TE-3B59
<p>Together with ongoing experimental efforts to detect gravitational waves, several fronts of theoretical research are presently being pursued, including second-generation detector design, data analysis, and numerical-relativity simulations of sources. This thesis presents a study in each of these topics: i) The noise in the most sensitive frequency bands in second-generation ground-based gravitational-wave interferometers is dominated by the thermal noise of the test masses. One way to reduce test-mass thermal noise is to modify shape of the laser beam so that it better averages over the thermal fluctuations. When edge effects are neglected, the test-mass thermal noise is related to the beam shape by simple scaling laws. This thesis presents a rigorous derivation of these laws, along with estimates of the errors made by neglecting edge effects. ii) An important class of gravitational-wave sources for space-based gravitational-wave interferometers is extreme-mass-ratio inspirals (EMRIs). These are binaries in which an object of a few solar masses spirals into a (typically million-solar-mass) supermassive black hole (or, if any exist, other type of massive body). Ryan (1995) proved that, under certain simplifying assumptions, the spacetime geometry is redundantly encoded in EMRI waves. One of Ryan's assumptions was negligible tidal coupling. After first finding that only the time-varying part of the induced tide is unambiguously defined when the central body is a black hole, this thesis extends Ryan's theorem by showing that both the spacetime geometry and details of the tidal coupling are encoded in EMRI waves. iii) Merging black holes with comparable masses are important sources of gravitational waves for ground-based detectors. The gravitational waves near the time of merger can only be predicted by numerically solving the Einstein equations. Initial data in numerical simulations must contain the desired physical content but also satisfy the Einstein constraint equations. But conventional binary-black-hole initial data has physical flaws: a nonzero orbital eccentricity and an initial, unphysical pulse of spurious gravitational radiation. Using the Caltech-Cornell pseudospectral code, this thesis develops and implements methods to reduce both of these effects.</p>https://thesis.library.caltech.edu/id/eprint/1987Topics in Numerical Relativity: The Periodic Standing-Wave Approximation, the Stability of Constraints in Free Evolution, and the Spin of Dynamical Black Holes
https://resolver.caltech.edu/CaltechETD:etd-05252007-143511
Authors: {'items': [{'email': 'owen@tapir.caltech.edu', 'id': 'Owen-Robert-Philip', 'name': {'family': 'Owen', 'given': 'Robert Philip'}, 'show_email': 'NO'}]}
Year: 2007
DOI: 10.7907/464A-4Y76
<p>This thesis concerns numerical relativity, the attempt to study Einstein's theory of gravitation using numerical discretization. The goal of the field, the study of gravitational dynamics in cases where symmetry reduction or perturbation theory are not possible, finally seems to be coming to fruition, at least for the archetypal problem of the inspiral and coalescence of binary black hole systems. This thesis presents three episodes that each bear some relationship to this story.</p>
<p>Chapters 2 and 3 present previously published work in collaboration with Richard Price and others on the so-called periodic standing-wave (PSW) approximation for binary inspiral. The approximation is to balance outgoing radiation with incoming radiation, stabilizing the orbit and making the problem stationary in a rotating frame. Chapters 2 and 3 apply the method to the problem of co-orbiting charges coupled to a nonlinear scalar field in three dimensions.</p>
<p>Chapters 4, 5, and 6 concern the stability of constraint fields in conventional numerical relativity simulations. Chapter 4 (also previously published work, in collaboration with the Caltech numerical relativity group, along with Michael Holst and Lawrence Kidder) presents a method for immediately correcting violations of constraints after they have arisen. Chapters 5 and 6 present methods to "damp" away constraint violations dynamically in two specific contexts. Chapter 5 (previously published work in collaboration with the Caltech numerical relativity group and Lawrence Kidder) presents a first-order linearly degenerate symmetric hyperbolic representation of Einstein's equations in generalized harmonic gauge. A representation is presented that stabilizes all constraints, including those that appear when the system is written in first-order form. Chapter 6 presents a generalization of the Kidder-Scheel-Teukolsky evolution systems that provides much-improved stability. This is investigated with numerical simulations of a single black hole spacetime.</p>
<p>Finally, chapter 7 presents work in progress to implement code to calculate the spin of black holes in numerical simulations. This requires a well-defined generalization of the concept of "rotation generators" on topological two-spheres that may not have any true Killing vectors. I present a new method for defining these fields, and results of a numerical code that computes them.</p>https://thesis.library.caltech.edu/id/eprint/2073Feedback Control of Brownian Motion for Single-Particle Fluorescence Spectroscopy
https://resolver.caltech.edu/CaltechETD:etd-10092006-165831
Authors: {'items': [{'id': 'Berglund-Andrew-John', 'name': {'family': 'Berglund', 'given': 'Andrew John'}, 'show_email': 'NO'}]}
Year: 2007
DOI: 10.7907/EBKX-BP40
The stochastic Brownian motion of individual particles in solution constrains the utility of single-particle fluorescence microscopy both by limiting the dwell time of particles in the observation volume and by convolving their internal degrees of freedom with their random spatial trajectories. This thesis describes the use of active feedback control to eliminate these undesirable effects. We designed and implemented a feedback tracking system capable of locking the position of a fluorescent particle to the optic axis of our microscope, i.e., capable of tracking the two-dimensional, planar Brownian motion of a free particle in solution. A full theoretical description of the experiment is given in the language of linear stochastic control theory. The model describes both the statistics of the tracking system and provides a generalization of the theory of open-loop Fluorescence Correlation Spectroscopy (FCS) that accounts for fluctuations in fluorescence arising from competition between diffusion and damping. We find excellent agreement between theory and experiment. Using fluorescent polymer microspheres as test particles, we find that the observation time for these particles can be increased by 2-3 orders of magnitude over the open-loop scenario. The system achieves nearly optimal performance for moderately fast-moving particles at very low fluorescent count rates, comparable to those of a single fluorescent protein molecule. The system can classify particles in a binary mixture based on a real-time estimate of their diffusion coefficients (differing by a factor of ~4), achieving 90% success using fewer than 600 photons detected over 120 ms. Future directions for both the experimental and theoretical techniques are briefly discussed.https://thesis.library.caltech.edu/id/eprint/3996Topics in Gravitational Physics: Tidal Coupling in Gravitational Wave Searches and Mach’s Principle
https://resolver.caltech.edu/CaltechETD:etd-05212007-004257
Authors: {'items': [{'id': 'Fang-Hua', 'name': {'family': 'Fang', 'given': 'Hua'}, 'show_email': 'NO'}]}
Year: 2007
DOI: 10.7907/D99H-J577
<p>The gravitational waves emitted by a compact object inspirling into a massive central body (e.g., a massive black hole) contain exquisite information about the spacetime geometry around that body and the tidal interaction (energy and angular momentum transfer) between the body and the inspiraling object's orbit. The first part (chapter 2--4) of this thesis studies several topics in the frame work of gravitation-wave search. In chapter 2 (in collaboration with G. Lovelace), we study the tidal interaction between a non-rotating black hole and circularly orbiting moon. Our analysis shows that the static induced quadrupole moment of the black hole is inherently ambiguous. In chapter 3, we give a survey of initial explorations of the prospects for using Advanced LIGO to detect gravitational waves from intermediate-mass-ratio inspirals (IMRIs))---analogous to the extreme-mass-ratio inspirals (EMRIs) targeted by LISA. We describe initial estimates of the detection range and the number of IMRI wave cycles in the Advanced LIGO band. We also give a detailed analysis of Advanced LIGO's accuracy for measuring the tide-induced energy transfer between the central black hole and the orbit. In chapter 4 (in collaboration with S. Babak, J. R. Gair, K. Glampedakis, and S. Hughes), we describe a new waveform-generating scheme in the context of LISA's data analysis for EMRI waves. The result is a family of "Numerical Kludge" waveforms, which share remarkable agreement with the more rigorous, but more computational-intensive Teukolsky-based waveforms.</p>
<p>The second part (chapter 5) of this thesis (in collaboration with K. S. Thorne) discusses another prediction from general relativity, the dragging of inertial frames, in connection with Mach's principle. We idealize our universe as a homogeneous, isotropic expanding, and slowly rotating sphere, surrounded by vacuum. We find that as the universe expands, the frame dragging weakens at its center; and that at later times inertia at the center completely breaks free of the grip of the universe's rotating matter.</p>https://thesis.library.caltech.edu/id/eprint/1915Continuous Quantum Measurement of Cold Alkali-Atom Spins
https://resolver.caltech.edu/CaltechETD:etd-02172007-172548
Authors: {'items': [{'email': 'john.stockton@gmail.com', 'id': 'Stockton-John-Kenton', 'name': {'family': 'Stockton', 'given': 'John Kenton'}, 'show_email': 'YES'}]}
Year: 2007
DOI: 10.7907/7PTX-AB16
<p>The field of quantum metrology concerns the physical measurement of sensors with a precision comparable to fundamental limits set by quantum mechanics. It is possible to outperform naive interpretations of these limits by using entangled states of the sensor system. One example is that of a spin-squeezed state, in which the uncertainty of one variable is decreased at the expense of another while still obeying Heisenberg's uncertainty principle, improving rotation sensitivity along a chosen axis. These states are potentially useful in devices including atomic clocks, inertial sensors, and magnetometers.</p>
<p>Any model of a quantum metrology device must respect the fact that physical measurements are not passive, as imagined classically, but necessarily invasive. Far from being a negative feature, well-understood quantum measurement can conditionally drive a system into desirable entangled states, including spin-squeezed states. Furthermore, the fundamental randomness of this process can, in principle, be removed with real-time feedback control, motivating an adaptation of classical feedback concepts to the quantum realm.</p>
<p>In this thesis, I describe these ideas in the context of one experimental example. A laser-cooled cloud of cesium spins is polarized along one axis via optical pumping and, subsequently, a linearly polarized far-off resonant probe beam traverses the sample. Due to the interaction Hamiltonian, the optical polarization rotates by an amount nominally proportional to one spin component of the collective spin state, enacting a weak, continuous, nondemolition measurement of that collective variable. This optical Faraday rotation is then measured with a polarimeter and the inherently noisy result used to condition the collective atomic state via a quantum filter, or stochastic master equation. Ideally, this process is capable of producing spin-squeezed states via the measurement itself.</p>
<p>The details of this measurement are investigated in depth, including a derivation of the nonideal polarizability Hamiltonian, an analysis of the projection process with control, and a derivation of the magnetometry sensitivity. Experimentally, we demonstrate continuous measurement of the collective spin state with a large single-shot signal-to-noise ratio and verify many predictions of the model. Finally, we describe attempts to observe the atomic projection noise, which would infer the preparation of spin-squeezed states.</p>https://thesis.library.caltech.edu/id/eprint/667Crystalline Whispering Gallery Mode Resonators for Quantum and Nonlinear Optics
https://resolver.caltech.edu/CaltechETD:etd-05132008-133522
Authors: {'items': [{'email': 'grudinin@jpl.nasa.gov', 'id': 'Grudinin-Ivan-Sergeevich', 'name': {'family': 'Grudinin', 'given': 'Ivan Sergeevich'}, 'show_email': 'NO'}]}
Year: 2008
DOI: 10.7907/3J52-QW65
<p>This work describes a series of projects and technology developments aimed at the realization of a solid-state photonic-ionic trap for quantum optics experiments. The projects however, are not constrained to this goal and explore the fields of nonlinear optics and fabrication techniques.</p>
<p>Fabri-Perot resonators have transformed the optical technology and can be found in many devices that utilize laser radiation. Whispering gallery mode resonators (WGMR) are relatively new elements and have such advantages as compactness, highest optical quality factors, and relative ease of fabrication. Small optical mode volume and long storage times allow record low thresholds of various nonlinear processes. Raman and Brillouin lasing, second and third harmonic generation, parametric oscillations and four wave mixing have all been enhanced in WGM resonators. Compared to glass microspheres, crystalline WGM resonators have higher nonlinear coefficients, may not be sensitive to water vapor, and have generally higher purity leading to record optical quality (Q) factors. Zero phonon lines of ions in crystals enable applications in cavity QED with single ions.</p>
<p>A novel application of diamond turning to fabrication of axially symmetric crystalline optical resonators is described. This technique enabled crystalline WGM microresonators, multiple resonators coupled via the evanescent field, and a single mode resonator. Crystalline resonators having a record high optical Q of 10<sup>11</sup> were demonstrated. Fundamental limits of the Q factor were investigated and Q=10<sup>15</sup> was predicted at cryogenic temperatures. Record low threshold and high efficiency of stimulated Raman and Brillouin scattering led to the first observations of these effects in crystalline cavities. Brillouin and Raman lasers based on WGM resonators are expected to have very narrow linewidth. A cryogenic setup was developed that allowed observation of WG modes at low temperatures. Crystalline cavity was used as a reference for narrowing a linewidth of a commercial diode laser with a Pound-Drever-Hall technique for the first time. A device based on a fused silica WGMR was used to generate beams with large angular momenta. In addition, a Fabri-Perot cavity was used to sense thermal expansion of mirrors to derive thermal expansion and temperature conductivity of thin optical coatings.</p>
https://thesis.library.caltech.edu/id/eprint/5186Design and Deployment of BICEP: A Novel Small-Aperture CMB Polarimeter to Test Inflationary Cosmology
https://resolver.caltech.edu/CaltechETD:etd-10092007-162326
Authors: {'items': [{'email': 'kiwon@stanford.edu', 'id': 'Yoon-Ki-Won', 'name': {'family': 'Yoon', 'given': 'Ki Won'}, 'show_email': 'NO'}]}
Year: 2008
DOI: 10.7907/5Q7T-YN18
<p>BICEP is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. BICEP consists of a 250 mm aperture refractive telescope that provides an instantaneous field-of-view of 17 degrees with angular resolution of 0.93 and 0.60 degrees at 100 GHz and 150 GHz, respectively, coupled to a focal plane of 98 polarization-sensitive bolometers.</p>
<p>This work details the design and characterization of the instrument, with discussion of preliminary results from data collected beginning inaugural 2006 observing season at the South Pole through present. Instrument testing indicates that the systematic contaminations of the B-mode will be below the threshold required for probing down to a tensor/scalar ratio of r = 0.1. Positive detection of the E-mode polarization is reported, while the B-mode maps are consistent with noise. In addition, the fractional polarization of the galactic foreground is constrained to f < 0.05 at moderate galactic latitudes.</p>
https://thesis.library.caltech.edu/id/eprint/4002Optofluidic Dye Lasers
https://resolver.caltech.edu/CaltechETD:etd-09142007-143251
Authors: {'items': [{'email': 'zhenyu@gwu.edu', 'id': 'Li-Zhenyu', 'name': {'family': 'Li', 'given': 'Zhenyu'}, 'orcid': '0000-0002-7752-6225', 'show_email': 'NO'}]}
Year: 2008
DOI: 10.7907/AQQR-QG80
<p>Optofluidic dye lasers refer to a class of liquid dye lasers, usually on a microfabricated device, in which the adaptive nature of the liquid gain medium allows the dynamical control of the laser properties. Miniaturizing liquid dye lasers onto a microfluidic device not only results in compact, easy-to-maintain and safe dye laser systems, but also provides unprecedented optical performances such as precise spatial mode control, low threshold, and automatic fluidic tuning. Equally important, such on-chip liquid laser sources represent an important component for "lab-on-a-chip" systems.</p>
<p>This thesis studies the implementations of optofluidic dye lasers on polydimethylsiloxane (PDMS) based microfluidic devices. Replica molding soft lithography was used to fabricate monolithic PDMS devices which contain both wavelength-scale optical structures and large-sized microfluidic channels. We have demonstrated narrow linewidth single mode DFB lasers, simultaneous operation of integrated DFB laser arrays with a single pump, multiple color lasing from the same DFB cavity, continuous mechanical wavelength tuning over a 60nm range, microfluidic wavelength tuning, single mode liquid-core microring lasers using Vernier effect, liquid-cladding evanescent gain DFB lasers, and monolithic integration with PDMS microfluidic circuits. Typical laser thresholds achieved are well within the reach of commercial high power laser diodes, thus enabling the implementations of compact tunable laser sources for portable “lab-on-a-chip” devices. The impressive performances, diverse geometries and applications clearly demonstrate the power of optofluidic integration and adaptation.</p>
https://thesis.library.caltech.edu/id/eprint/5251Experiments with Toroidal Microresonators in Cavity QED
https://resolver.caltech.edu/CaltechETD:etd-05282009-101209
Authors: {'items': [{'email': 'sk8lizzy@gmail.com', 'id': 'Connolly-Elizabeth-Wilcut', 'name': {'family': 'Connolly', 'given': 'Elizabeth Wilcut'}, 'show_email': 'YES'}]}
Year: 2009
DOI: 10.7907/78XV-CS35
Advances made pertaining to strong interactions between single photons of light and single atoms have great potential in the field of quantum information. However, scalability is a limiting factor in the applicability of current technologies (such as an atom in the mode of a Fabry-Perot resonator) due to difficulties in alignment and fabrication. Toroial resonators, however, are fabricated lithographically on silicon wafers, and are therefore easily scalable. Light is coupled into a toroid by tapered optical fiber, allowing for the efficient retrieval of photons from the resonator mode that is necessary if multiple resonators are to be eventually coupled to one another. We have demonstrated interactions between single atoms of cesium and a toroidal resonator that lie in the regime of strong coupling since the rate of coupling between an atom and the cavity mode, g0 m = (50±12) MHz, is much larger than the dissipative rates of the system (gamma, kappa)/2pi ~ (2.6, 18) MHz. To further expand upon the usefulness of toroids in cavity QED, I have striven to improve the way that toroids are characterized and coupled. An apparatus which semi-automates the characterization process reduces the length of time a toroid is outside of vacuum, thus limiting environmental degradation. To help in better understanding the process of pulling tapered fibers, the efficiency and characteristic quantities have been detailed. Similarly, the behavior of a toroid resonance as a function of coupling strength was quantified. Preliminary locking of the coupling by controlling the separation between the taper and toroid has been accomplished. This locking will allow the next generation of atom-toroid coupling to require less human intervention and therefore be more efficient. https://thesis.library.caltech.edu/id/eprint/2218Observation of Cosmic Microwave Background Polarization with BICEP
https://resolver.caltech.edu/CaltechETD:etd-10052008-101916
Authors: {'items': [{'email': 'hsinc@princeton.edu', 'id': 'Chiang-Hsin-Cynthia', 'name': {'family': 'Chiang', 'given': 'Hsin Cynthia'}, 'orcid': '0000-0002-4098-9533', 'show_email': 'NO'}]}
Year: 2009
DOI: 10.7907/RA1D-V074
Background Imaging of Cosmic Extragalactic Polarization (BICEP) is a bolometric polarimeter that has been optimized to target the B-mode of the cosmic microwave background (CMB) polarization at degree angular scales, which is a sensitive probe of the energy scale of inflation. The instrument's focal plane comprises 49 pairs of polarization-sensitive bolometers operating at 100 and 150 GHz, and the 25-cm aperture refractive optics provide degree-scale resolution over a 17 degree instantaneous field of view. The compact design enables sufficient control of instrumental polarization systematics to attain a projected final sensitivity corresponding to a tensor-to-scalar ratio of 0.1. This thesis describes the design, performance, and preliminary science results from BICEP, which has been observing the CMB from the South Pole since January 2006. After the first two seasons of operation, the EE, TE, and TT power spectra are measured with high precision at 30 < ell < 300, and BB is consistent with zero. BICEP has also observed the Galactic plane, and polarized emission is mapped with high signal-to-noise.
https://thesis.library.caltech.edu/id/eprint/3938Cavity Optomechanics in Photonic and Phononic Crystals: Engineering the Interaction of Light and Sound at the Nanoscale
https://resolver.caltech.edu/CaltechTHESIS:01192010-152952905
Authors: {'items': [{'email': 'matt@caltech.edu', 'id': 'Eichenfield-Matthew-S', 'name': {'family': 'Eichenfield', 'given': 'Matthew S.'}, 'show_email': 'NO'}]}
Year: 2010
DOI: 10.7907/8Q52-8C38
<p>The dynamic back-action caused by electromagnetic forces (radiation pressure) in optical and microwave cavities is of growing interest. Back-action cooling, for example, is being pursued as a means of achieving the quantum ground state of macroscopic mechanical oscillators. Work in the optical domain has revolved around millimeter- or micrometer-scale structures using the radiation pressure force. By comparison, in microwave devices, low-loss superconducting structures have been used for gradient-force-mediated coupling to a nanomechanical oscillator of picogram mass. In this thesis, two different nanometer-scale structures that use combinations of gradient and radiation pressure optical forces are described theoretically and demonstrated experimentally. These structures merge the fields of cavity optomechanics and nanomechanics into nano-optomechanical systems (NOMS).</p>
<p>The first device, the Zipper optomechanical cavity, consists of a pair of doubly-clamped nanoscale beams separated by approximately 100 nanometers, each beam having a mass of 20 picograms and being patterned with a quasi-1D photonic crystal bandgap cavity. The optical mode of the coupled system is exquisitely sensitive to differential motion of the beams, producing optomechanical coupling right at the fundamental limit set by optical diffraction. The mechanical modes of the beam probed with a background sensitivity only a factor of 4 above the standard quantum limit, and the application of less than a milliwatt of optical power is shown to increase the mechanical rigidity of the system by almost an order of magnitude.</p>
<p>The second device focuses on just one of the doubly-clamped nanoscale beams of the Zipper. We show that, in addition to a photonic bandgap cavity, the periodic patterning of the beam also produces a phononic bandgap cavity with localized mechanical modes having frequencies in the microwave regime. We call these photonic and phononic crystal bandgap cavities optomechanical crystals. Because the optical and mechanical modes occupy a volume more than 100,000 times smaller than the volume of a single human cell, the optomechanical interaction in this system is again at the fundamental limit set by optical diffraction. The miniscule effective volume of the mechanical mode corresponds to effective motional masses in the femtogram regime, which, coupled with the enormous optomechanical interaction and high optical and mechanical quality factors, allows transduction of microwave-frequency mechanical motion nearly at the standard quantum limit, with the standard quantum limit easily within reach with simple modifications of the experimental apparatus. The combination of the small motional mass and strong optomechanical coupling allows each trapped photon to drive motion of an acoustic mode with a force more than 15 times the weight of the structure. This provides a powerful method for optically actuating microwave-frequency mechanical oscillators on a chip, and we demonstrate an on-chip phonon laser that emits over 1012 microwave-frequency phonons per second with a ratio of frequency to linewidth of 2 million—characteristics similar to those of the first optical lasers. With the ability to readily interconvert photons and microwave-frequency phonons on the surface of a microchip, new chip-scale technologies can be created. We discuss the future of optomechanical crystals and provide new methods of calculating all the otptomechanical properties of the structures.</p>https://thesis.library.caltech.edu/id/eprint/5530Applications of Micro/Nanoscale Optical Resonators: Plasmonic Photodetectors and Double-Disk Cavity Optomechanics
https://resolver.caltech.edu/CaltechTHESIS:03072010-230109724
Authors: {'items': [{'email': 'jessiecrosenberg@gmail.com', 'id': 'Rosenberg-Jessie-C', 'name': {'family': 'Rosenberg', 'given': 'Jessie C.'}, 'show_email': 'NO'}]}
Year: 2010
DOI: 10.7907/GA8B-F134
<p>Optical resonators present the potential to serve vital purposes in many emergent technologies that require spectral filtering, high optical intensities, or optical delays. By scaling down the optical resonators to the micro or nanoscale, the relevant phenomena can increase significantly in magnitude, while the device geometries become suitable for chip-scale and integrated processing. In this thesis, research is presented on several valuable resonator geometries and implementations, beginning with a more standard all-optical design, and continuing on to investigate the novel phenomena and applications which are made possible when optical and mechanical structures can be synergistically combined.</p>
<p>First, the design and experimental implementation of a plasmonic photonic crystal spectral and polarization filtering element is presented. This resonator scheme, in addition to allowing for a tailorable frequency and polarization response for single detector pixels, also increases the absorption of a thin layer of detector material by utilizing the unique optical properties of metal to confine light more tightly within the detector active region. Demonstrated in the valuable mid-infrared regime, this method of producing pixel-integrated multispectral detectors could find application in biological sensing and spectroscopy, missile tracking and guidance, and night vision.</p>
<p>Following this discussion, progress is presented in the relatively new field of cavity optomechanics: utilizing mechanically compliant optical resonators to couple to, control, and read out mechanical motion via optical forces. The use of optical resonators allows the generally weak optical forces to be increased in strength by orders of magnitude due to the many passes light makes within the resonator, while miniaturizing optomechanical devices into a convenient form factor for on-chip applications. Using a fully silicon-compatible double-disk-geometry optomechanical resonator, extremely large optomechanical coupling and very high optical quality factors are shown, enabling the demonstration of regenerative mechanical amplification, high compression factor optomechanical cooling, coherent mechanical mode mixing, and wide-bandwidth all-optical wavelength routing. Applications to ground-state cooling of mesoscopic devices, tunable optical buffering, photonic-phononic quantum state transfer, channel routing/switching, pulse trapping/release, and tunable lasing are discussed.</p>https://thesis.library.caltech.edu/id/eprint/5581Coherent Control of Entanglement with Atomic Ensembles
https://resolver.caltech.edu/CaltechTHESIS:05192011-130117986
Authors: {'items': [{'email': 'kyung114@gmail.com', 'id': 'Choi-Kyung-Soo', 'name': {'family': 'Choi', 'given': 'Kyung Soo'}, 'show_email': 'NO'}]}
Year: 2011
DOI: 10.7907/9T7P-2C53
<p>Quantum networks are composed of quantum nodes which coherently interact by way of quantum channels. They offer powerful capabilities for quantum computation, communication, and metrology. A generic requirement for these realizations is the capability to generate and store quantum states among multiple quantum nodes, and to disseminate these resources throughout the network via the quantum channels. In this thesis, I describe a series of experiments whereby single excitations in atomic ensembles are strongly coupled to optical modes and provide efficient means for the coherent control of entangled states between matter and light.</p>
<p>By following the seminal proposal by Duan et al., we have generated measurement-induced entanglement of an excitation between two cold atomic ensembles. Using this system, we investigated the relationship for the global bipartite entanglement and local correlations in its subsystems.</p>
<p>In addition, we achieved functional quantum nodes for entanglement distribution. Two pairs of remote ensembles at two quantum nodes were prepared into entangled states in a heralded and asynchronous fashion by the conditional controls of the entanglement. The quantum states of the ensembles were then distributed into polarization entangled states of photons. We also prepared an analogous quantum state and transferred the nonlocal coherence between two pairs of heralded entangled atomic ensembles, providing a step towards entanglement connection.</p>
<p>Beyond such probabilistic approaches, we demonstrated an experiment where entanglement between two quantum memories is created by the reversible and deterministic mapping of an entangled state of light via dynamic electromagnetically induced transparency. This experiment opens novel prospects of integrating hybrid quantum systems by way of reversible quantum interfaces between light and matter.</p>
<p>Then, we extended our work to multipartite quantum systems. We theoretically investigated the characterization of multipartite mode-entangled states by way of quantum uncertainty relations, and introduced theoretical tools to verify the entanglement orders in multipartite systems. In particular, we achieved entanglement for one delocalized photon among multiple optical modes (N > 2).</p>
<p>Finally, we have achieved measurement-induced entanglement of spin waves among four quantum memories. The individual atomic components for the entangled W state of the four ensembles were then coherently converted into four propagating entangled beams of light via superradiant emissions. We observed the statistical and dynamic transitions for the multipartite entangled spin waves. Experiments described in this thesis thereby represent significant advances of experimental and theoretical capabilities to generate, store, transfer, and characterize entanglement of matter and light over quantum networks.</p>https://thesis.library.caltech.edu/id/eprint/6410Nonisochronous Oscillations in Piezoelectric Nanomechanical Resonators
https://resolver.caltech.edu/CaltechTHESIS:06082012-140554238
Authors: {'items': [{'email': 'mathsquared@gmail.com', 'id': 'Matheny-Matthew-Hayward', 'name': {'family': 'Matheny', 'given': 'Matthew Hayward'}, 'show_email': 'NO'}]}
Year: 2012
DOI: 10.7907/2P71-JT64
<p>Nanoelectromechanical systems (NEMS) have proven an excellent test bed for exploring nonlinear dynamics due to short decay times, weak nonlinearities, and large quality factors. In contrast to previous research in nonlinear dynamics involving driven or phase fixed NEMS, where time is referenced by an external source, we describe phenomena classified by phase free phenomena. Here we describe NEMS embedded into feedback oscillators with weak nonlinearities.</p>
<p>We make measurements of this mechanical nonlinearity by developing a transduction scheme, the piezoelectric/piezoresistive (PZE/PZR) transduction, which emphasizes the detector dynamic range over absolute sensitivity. Using these measurements, projections on quantum nondemolition schemes involving the mechanical nonlinearity as a detector are made. These measurements also are important for understanding the detection limits of NEMS sensor technology, which uses a mechanical resonator as a frequency reference in a phase locked loop (PLL).</p>
<p>This work identifies ways to reduce noise within ‘nonlinear’ feedback oscillators, and these results have implications for sensing systems using nonlinear mechanical resonators embedded in PLLs. Since the mechanical nonlinearity of PZE/PZR resonators can be accurately calibrated, we make predictions for the behavior of these dynamical systems based on the given mechanical and electrical parameters. We show, theoretically, that local isochronicity above critical nonlinear amplitudes can create special operating points in feedback oscillators at which parametric fluctuations may cause less phase noise in the oscillator than in feedback oscillators driven below critical amplitudes. For these predictions, we present data that show quantitative agreement for the amplitude and frequency, and qualitative agreement for the phase noise.</p>
<p>Finally, we show synchronization, assisted by nonisochronicity, between two feedback NEMS oscillators. We develop a general theoretical framework for two saturated feedback oscillators which use resonators with nonlinear stiffness. In the limit of small coupling, we show that the system obeys the Adler equation with analytical predictions for the oscillators’ individual amplitudes and net frequency difference. We develop an experiment in which the three important parameters of the system (detuning, nonisochronicity, and coupling) can be tuned, and show data that agrees with the predictions for a large range of coupling. We include data on phase slipping between two oscillators in which the aperiodic frequency difference is clearly observed. Finally, we present data on phase noise in synchronized oscillators.</p>https://thesis.library.caltech.edu/id/eprint/7149Studies of Exciton Condensation and Transport in Quantum Hall Bilayers
https://resolver.caltech.edu/CaltechTHESIS:09262011-144749993
Authors: {'items': [{'email': 'afinck@gmail.com', 'id': 'Finck-Aaron-David-Kiyoshi', 'name': {'family': 'Finck', 'given': 'Aaron David Kiyoshi'}, 'show_email': 'NO'}]}
Year: 2012
DOI: 10.7907/PQJV-SB92
This thesis is a report of the transport properties of bilayer two-dimensional electron systems found in GaAs/AlGaAs double quantum well semiconductor heterostructures. When a strong perpendicular magnetic field is applied so that the total Landau filling factor is equal to one and if the two layers are close enough together, a novel quantum Hall (QH) state with strong interlayer correlations can form. This QH state is often described as an excitonic condensate, in which electrons in one layer pair with holes in the other. As neutral particles, excitons feel no Lorentz force and are not confined to the edges of the bilayer system like charged quasiparticles are. Instead, excitons are expected to be able to move freely through the bulk and even flow without any dissipation under proper conditions (i.e.,~excitonic superfluidity). Counterflow studies that directly probe the bulk verify this exciton transport in the electrically insulating interior. We also report on studies of the phase boundary between the correlated and uncorrelated phases at total Landau filling factor one as the effective interlayer separation is tuned. When both phases are fully spin polarized at high Zeeman energy, the phase transition is much broader than when the uncorrelated phase is incompletely polarized at low Zeeman energy. This suggests a possible change in the nature of the phase transition in the regime of complete spin polarization.https://thesis.library.caltech.edu/id/eprint/6689Scanning Tunneling Spectroscopic Studies on High-Temperature Superconductors and Dirac Materials
https://resolver.caltech.edu/CaltechTHESIS:05142013-151159910
Authors: {'items': [{'email': 'mindtex@gmail.com', 'id': 'Teague-Marcus-Lawrence', 'name': {'family': 'Teague', 'given': 'Marcus Lawrence'}, 'show_email': 'YES'}]}
Year: 2013
DOI: 10.7907/M8FW-S641
<p>This thesis details the investigations of the unconventional low-energy quasiparticle excitations in electron-type cuprate superconductors and electron-type ferrous superconductors as well as the electronic properties of Dirac fermions in graphene and three-dimensional strong topological insulators through experimental studies using spatially resolved scanning tunneling spectroscopy (STS) experiments.</p>
<p>Magnetic-field- and temperature-dependent evolution of the spatially resolved quasiparticle spectra in the electron-type cuprate La<sub>0.1</sub>Sr<sub>0.9</sub>CuO<sub>2</sub> (La-112) T<sub>C</sub> = 43 K, are investigated experimentally. For temperature (T) less than the superconducting transition temperature (TC), and in zero field, the quasiparticle spectra of La-112 exhibits gapped behavior with two coherence peaks and no satellite features. For magnetic field measurements at T < TC, first ever observation of vortices in La-112 are reported. Moreover, pseudogap-like spectra are revealed inside the core of vortices, where superconductivity is suppressed. The intra-vortex pseudogap-like spectra are characterized by an energy gap of V<sub>PG</sub> = 8.5 ± 0.6 meV, while the inter-vortex quasiparticle spectra shows larger peak-to-peak gap values characterized by Δ<sub>pk-pk</sub>(H) >V<sub>PG</sub>, and Δ<sub>pk-pk</sub> (0)=12.2 ± 0.8 meV > Δ<sub>pk-pk</sub> (H > 0). The quasiparticle spectra are found to be gapped at all locations up to the highest magnetic field examined (H = 6T) and reveal an apparent low-energy cutoff at the V<sub>PG</sub> energy scale.</p>
<p>Magnetic-field- and temperature-dependent evolution of the spatially resolved quasiparticle spectra in the electron-type "122" iron-based Ba(Fe<sub>1-x</sub>Co<sub>x</sub>)<sub>2</sub>A<sub>s2</sub> are investigated for multiple doping levels (x = 0.06, 0.08, 0.12 with T<sub>C</sub>= 14 K, 24 K, and 20 K). For all doping levels and the T < T<sub>C</sub>, two-gap superconductivity is observed. Both superconducting gaps decrease monotonically in size with increasing temperature and disappear for temperatures above the superconducting transition temperature, T<sub>C</sub>. Magnetic resonant modes that follow the temperature dependence of the superconducting gaps have been identified in the tunneling quasiparticle spectra. Together with quasiparticle interference (QPI) analysis and magnetic field studies, this provides strong evidence for two-gap sign-changing s-wave superconductivity.</p>
<p>Additionally spatial scanning tunneling spectroscopic studies are performed on mechanically exfoliated graphene and chemical vapor deposition grown graphene. In all cases lattice strain exerts a strong influence on the electronic properties of the sample. In particular topological defects give rise to pseudomagnetic fields (B ~ 50 Tesla) and charging effects resulting in quantized conductance peaks associated with the integer and fractional Quantum Hall States.</p>
<p>Finally, spectroscopic studies on the 3D-STI, Bi<sub>2</sub>Se<sub>3</sub> found evidence of impurity resonance in the surface state. The impurities are in the unitary limit and the spectral resonances are localized spatially to within ~ 0.2 nm of the impurity. The spectral weight of the impurity resonance diverges as the Fermi energy approaches the Dirac point and the rapid recovery of the surface state suggests robust topological protection against perturbations that preserve time reversal symmetry.</p>
https://thesis.library.caltech.edu/id/eprint/7709Measurement of Thermo-Optic Properties of Thin Film Dielectric Coatings
https://resolver.caltech.edu/CaltechTHESIS:08212012-185113285
Authors: {'items': [{'email': 'ghogin@gmail.com', 'id': 'Ogin-Gregory-H', 'name': {'family': 'Ogin', 'given': 'Gregory H.'}, 'show_email': 'NO'}]}
Year: 2013
DOI: 10.7907/A1CR-G214
We have carried out an experiment to test the theory of the thermo-optic response of a dielectric stack mirror coating and to measure parameters of interest in calculating thermo-optic noise. Specifically, we measured the coefficient of thermal expansion and the change of index of refraction with temperature (dn/dT ) for thin film silica (SiO<sub>2</sub>) and tantala (Ta<sub>2</sub>O<sub>5</sub>) in mirror coatings. These measurements were achieved by driving thermal fluctuations in such mirrors in one arm of a small Michelson interferometer. We report on the results of that experiment along with its potential implications for future gravitational wave detectors, and suggest next steps for this important line of investigation.https://thesis.library.caltech.edu/id/eprint/7189The Physics of Ultracold Neutrons and Fierz Interference in Beta Decay
https://resolver.caltech.edu/CaltechTHESIS:11022012-135115177
Authors: {'items': [{'email': 'hickerson@gmail.com', 'id': 'Hickerson-Kevin-Peter', 'name': {'family': 'Hickerson', 'given': 'Kevin Peter'}, 'show_email': 'NO'}]}
Year: 2013
DOI: 10.7907/K8CK-MQ14
<p>type of reflector that directs UCN upward in to vertical paths. Next we examine UCN passing through thin, multilayered foils. In the remaining sections we investigate the so-called Fierz interference term of free neutron beta decay, denoted b<sub>n</sub>. It is theorized that contributions to scalar and tensor interactions from physics beyond the Standard Model could be detectable in the spectrum of neutron beta decay, manifest as a nonzero value for b<sub>n</sub>. We investigate three techniques for measuring b<sub>n</sub>. The first is to use the primordial helium abundance fraction and compare that to predictive Big Bang nucleosynthesis calculations. Second we extract b<sub>n</sub> from the spectral shape generated by the 2010 data set of the UCNA experiment. Third, we discuss progress toward constructing the UCNb experimental prototype. We present the design of this new experiment that uses the UCN source at LANSCE for measuring b<sub>n</sub>, in which UCN are guided into a shielded 4π calorimeter where they are stored and decay. From Big Bang nucleosynthesis we can place the limit 0.021 < b<sub>n</sub> < 0.277 (90\% C.L.) on the neutron Fierz term and from the UCNA 2010 data we set -0.044 < b<sub>n</sub> < 0.218 (90\% C.L.).</p>
https://thesis.library.caltech.edu/id/eprint/7250Characterizing a Resonator Bolometer Array
https://resolver.caltech.edu/CaltechTHESIS:05312013-022124797
Authors: {'items': [{'id': 'Wernis-Rebecca-Ann', 'name': {'family': 'Wernis', 'given': 'Rebecca Ann'}, 'show_email': 'NO'}]}
Year: 2013
DOI: 10.7907/XPSC-WR14
High-background applications such as climate monitoring, biology and security applications demand a large dynamic range. Under such conditions ultra-high sensitivity is not required. The resonator bolometer is a novel detector which is well-suited for these conditions. This device takes advantage of the high-density frequency multiplexing capabilities of superconducting microresonators while allowing for the use of high-Tc superconductors in fabrication, which enables a modest (1-4 K) operating temperature and larger dynamic range than is possible with conventional microresonators. The moderate operating temperature and intrinsic multiplexability of this device reduce cost and allow for large pixel counts, making the resonator bolometer especially suitable for the aforementioned applications. A single pixel consists of a superconducting microresonator whose light-absorbing area is placed on a thermally isolated island. Here we present experimental results and theoretical calculations for a prototype resonator bolometer array. Intrinsic device noise and noise equivalent power (NEP) under both dark and illuminated conditions are presented. Under dark conditions the device sensitivity is limited by the thermal noise fluctuations from the bolometer legs. Under the experimental illuminated conditions the device was photon noise limited.https://thesis.library.caltech.edu/id/eprint/7786The Search for Gravitational Waves from the Coalescence of Black Hole Binary Systems in Data from the LIGO and Virgo Detectors. Or: A Dark Walk through a Random Forest
https://resolver.caltech.edu/CaltechTHESIS:06022014-104457554
Authors: {'items': [{'email': 'hodge.kari@gmail.com', 'id': 'Hodge-Kari-Alison', 'name': {'family': 'Hodge', 'given': 'Kari Alison'}, 'orcid': '0000-0002-1025-0420', 'show_email': 'YES'}]}
Year: 2014
DOI: 10.7907/HY26-2059
The LIGO and Virgo gravitational-wave observatories are complex and extremely sensitive strain detectors that can be used to search for a wide variety of gravitational waves from astrophysical and cosmological sources. In this thesis, I motivate the search for the gravitational wave signals from coalescing black hole binary systems with total mass between 25 and 100 solar masses. The mechanisms for formation of such systems are not well-understood, and we do not have many observational constraints on the parameters that guide the formation scenarios. Detection of gravitational waves from such systems — or, in the absence of detection, the tightening of upper limits on the rate of such coalescences — will provide valuable information that can inform the astrophysics of the formation of these systems. I review the search for these systems and place upper limits on the rate of black hole binary coalescences with total mass between 25 and 100 solar masses. I then show how the sensitivity of this search can be improved by up to 40% by the the application of the multivariate statistical classifier known as a random forest of bagged decision trees to more effectively discriminate between signal and non-Gaussian instrumental noise. I also discuss the use of this classifier in the search for the ringdown signal from the merger of two black holes with total mass between 50 and 450 solar masses and present upper limits. I also apply multivariate statistical classifiers to the problem of quantifying the non-Gaussianity of LIGO data. Despite these improvements, no gravitational-wave signals have been detected in LIGO data so far. However, the use of multivariate statistical classification can significantly improve the sensitivity of the Advanced LIGO detectors to such signals.https://thesis.library.caltech.edu/id/eprint/8463Magnetic Trapping of Atomic Tritium for Neutrino Mass Measurement
https://resolver.caltech.edu/CaltechTHESIS:07252014-082021105
Authors: {'items': [{'email': 'benjamin.mathias.clark@gmail.com', 'id': 'Clark-Benjamin-Mathias', 'name': {'family': 'Clark', 'given': 'Benjamin Mathias'}, 'show_email': 'NO'}]}
Year: 2014
DOI: 10.7907/N1FG-5H27
Improved measurement of the neutrino mass via β decay spectroscopy requires the development of new energy measurement techniques and a new β decay source. A promising proposal is to measure the β energy by the frequency of the cyclotron radiation emitted in a magnetic field and to use a high purity atomic tritium source. This thesis examines the feasibility of using a magnetic trap to create and maintain such a source. We demonstrate that the loss rate due to β decay heating is not a limiting factor for the design. We also calculate the loss rate due to evaporative cooling and propose that the tritium can be cooled sufficiently during trap loading as to render this negligible. We further demonstrate a design for the magnetic field which produces a highly uniform field over a large fraction of the trap volume as needed for cyclotron frequency spectroscopy while still providing effective trapping.https://thesis.library.caltech.edu/id/eprint/8605High Fidelity Probe and Mitigation of Mirror Thermal Fluctuations
https://resolver.caltech.edu/CaltechTHESIS:05282014-211250693
Authors: {'items': [{'email': 'taratogo@gmail.com', 'id': 'Chalermsongsak-Tara', 'name': {'family': 'Chalermsongsak', 'given': 'Tara'}, 'show_email': 'NO'}]}
Year: 2014
DOI: 10.7907/7202-WT21
<p>Thermal noise arising from mechanical loss in high reflective dielectric coatings is a significant source of noise in precision optical measurements. In particular, Advanced LIGO, a large scale interferometer aiming to observed gravitational wave, is expected to be limited by coating thermal noise in the most sensitive region around 30–300 Hz. Various theoretical calculations for predicting coating Brownian noise have been proposed. However, due to the relatively limited knowledge of the coating material properties, an accurate approximation of the noise cannot be achieved. A testbed that can directly observed coating thermal noise close to Advanced LIGO band will serve as an indispensable tool to verify the calculations, study material properties of the coating, and estimate the detector’s performance.</p>
<p>This dissertation reports a setup that has sensitivity to observe wide band (10Hz to 1kHz) thermal noise from fused silica/tantala coating at room temperature from fixed-spacer Fabry–Perot cavities. Important fundamental noises and technical noises associated with the setup are discussed. The coating loss obtained from the measurement agrees with results reported in the literature.
The setup serves as a testbed to study thermal noise in high reflective mirrors from different materials. One example is a heterostructure of Al<sub>x</sub>Ga<sub>1−x</sub>As (AlGaAs). An optimized design to minimize thermo–optic noise in the coating is proposed and discussed in this work.</p>https://thesis.library.caltech.edu/id/eprint/8416Multi-Model Inference Ranking and Applications to Physics at the Large Hadron Collider
https://resolver.caltech.edu/CaltechTHESIS:06122014-143656852
Authors: {'items': [{'email': 'valerelambert@gmail.com', 'id': 'Lambert-Valere-Regis-Westbrooke', 'name': {'family': 'Lambert', 'given': 'Valere Regis Westbrooke'}, 'show_email': 'YES'}]}
Year: 2014
DOI: 10.7907/43RG-P928
In the measurement of the Higgs Boson decaying into two photons the parametrization of an appropriate background model is essential for fitting the Higgs signal mass peak over a continuous background. This diphoton background modeling is crucial in the statistical process of calculating exclusion limits and the significance of observations in comparison to a background-only hypothesis. It is therefore ideal to obtain knowledge of the physical shape for the background mass distribution as the use of an improper function can lead to biases in the observed limits. Using an Information-Theoretic (I-T) approach for valid inference we apply Akaike Information Criterion (AIC) as a measure of the separation for a fitting model from the data. We then implement a multi-model inference ranking method to build a fit-model that closest represents the Standard Model background in 2013 diphoton data recorded by the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). Potential applications and extensions of this model-selection technique are discussed with reference to CMS detector performance measurements as well as in potential physics analyses at future detectors.https://thesis.library.caltech.edu/id/eprint/8520Nanoelectromechanical Membranes for Multimode Mass Spectrometry
https://resolver.caltech.edu/CaltechTHESIS:05272014-152108855
Authors: {'items': [{'email': 'jarvis.li360@gmail.com', 'id': 'Li-Jarvis', 'name': {'family': 'Li', 'given': 'Jarvis'}, 'show_email': 'YES'}]}
Year: 2014
DOI: 10.7907/R6T2-MP04
Nanoelectromechanical systems (NEMS) represent the next wave in miniaturizing various electrical and mechanical devices used in a variety of fields, such as physics, biology, and engineering. In particular, NEMS devices have high surface area to volume ratios, low power consumption, low mass, and extremely small footprints. These properties allow NEMS to explore more fundamental regimes of matter. Current NEMS mass spectrometry advancements have only utilized doubly-clamped beams and cantilevers. However to expand the measurement capabilities of NEMS mass spectrometry, we utilize a circular membrane geometry in order to build upon the existing measurements in 1 spatial dimension to measure mass spatially in 2-dimensions. Furthermore, membranes should provide a larger potential mass dynamic range. For this experiment, we utilize circular piezoelectric membranes of aluminum nitride and molybdenum stacks. For mass deposition, we utilize a technique known as matrix-assisted laser desorption/ionization (MALDI), which focuses a pulsed UV laser onto the desired sample embedded in a corresponding matrix. The energy causes a plume of particles to desorb off the sample and towards the device. As a particle lands on the device, we are able to deduce its mass from the shift in its resonant frequency. In particular we need to measure the first three resonant frequencies, since the frequency shifts also depend on the location the particle landed on the device. Here we show the viability of our detection setup, mass deposition setup, and our mass deposition results.https://thesis.library.caltech.edu/id/eprint/8400Crystals that Count! Physical Principles and Experimental Investigations of DNA Tile Self-Assembly
https://resolver.caltech.edu/CaltechTHESIS:05132014-142306756
Authors: {'items': [{'email': 'cevans@evanslabs.org', 'id': 'Evans-Constantine-Glen', 'name': {'family': 'Evans', 'given': 'Constantine Glen'}, 'orcid': '0000-0002-7053-1670', 'show_email': 'NO'}]}
Year: 2014
DOI: 10.7907/7FMK-9403
<p>Algorithmic DNA tiles systems are fascinating. From a theoretical perspective, they can result in simple systems that assemble themselves into beautiful, complex structures through fundamental interactions and logical rules. As an experimental technique, they provide a promising method for programmably assembling complex, precise crystals that can grow to considerable size while retaining nanoscale resolution. In the journey from theoretical abstractions to experimental demonstrations, however, lie numerous challenges and complications. </p>
<p>In this thesis, to examine these challenges, we consider the physical principles behind DNA tile self-assembly. We survey recent progress in experimental algorithmic self-assembly, and explain the simple physical models behind this progress. Using direct observation of individual tile attachments and detachments with an atomic force microscope, we test some of the fundamental assumptions of the widely-used kinetic Tile Assembly Model, obtaining results that fit the model to within error. We then depart from the simplest form of that model, examining the effects of DNA sticky end sequence energetics on tile system behavior. We develop theoretical models, sequence assignment algorithms, and a software package, StickyDesign, for sticky end sequence design.</p>
<p>As a demonstration of a specific tile system, we design a binary counting ribbon that can accurately count from a programmable starting value and stop growing after overflowing, resulting in a single system that can construct ribbons of precise and programmable length. In the process of designing the system, we explain numerous considerations that provide insight into more general tile system design, particularly with regards to tile concentrations, facet nucleation, the construction of finite assemblies, and design beyond the abstract Tile Assembly Model. </p>
<p>Finally, we present our crystals that count: experimental results with our binary counting system that represent a significant improvement in the accuracy of experimental algorithmic self-assembly, including crystals that count perfectly with 5 bits from 0 to 31. We show some preliminary experimental results on the construction of our capping system to stop growth after counters overflow, and offer some speculation on potential future directions of the field.</p>
https://thesis.library.caltech.edu/id/eprint/8232Cavity Enhanced Spectroscopies for Applications of Remote Sensing, Chemical Kinetics and Detection of Radical Species
https://resolver.caltech.edu/CaltechTHESIS:06032015-151007228
Authors: {'items': [{'email': 'novicebeing@gmail.com', 'id': 'Bui-Thinh-Quoc', 'name': {'family': 'Bui', 'given': 'Thinh Quoc'}, 'show_email': 'YES'}]}
Year: 2015
DOI: 10.7907/Z96D5QXW
This thesis describes applications of cavity enhanced spectroscopy towards applications of remote sensing, chemical kinetics and detection of transient radical molecular species. Both direct absorption spectroscopy and cavity ring-down spectroscopy are used in this work. Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was utilized for measurements of spectral lineshapes of O<sub>2</sub> and CO<sub>2</sub> for obtaining laboratory reference data in support of NASA’s OCO-2 mission. FS-CRDS is highly sensitive (> 10 km absorption path length) and precise (> 10000:1 SNR), making it ideal to study subtle non-Voigt lineshape effects. In addition, these advantages of FS-CRDS were further extended for measuring kinetic isotope effects: A dual-wavelength variation of FS-CRDS was used for measuring precise D/H and <sup>13</sup>C/<sup>12</sup>C methane isotope ratios (sigma>0.026%) for the purpose of measuring the temperature dependent kinetic isotope effects of methane oxidation with O(<sup>1</sup>D) and OH radicals. Finally, direct absorption spectroscopic detection of the trans-DOCO radical via a frequency combs spectrometer was conducted in collaboration with professor Jun Ye at JILA/University of Colorado. https://thesis.library.caltech.edu/id/eprint/8978New Physics Models in the Diphoton Final State at CMS
https://resolver.caltech.edu/CaltechTHESIS:01152016-102117113
Authors: {'items': [{'email': 'sezata@gmail.com', 'id': 'Wang-Ann-Miao', 'name': {'family': 'Wang', 'given': 'Ann Miao'}, 'show_email': 'NO'}]}
Year: 2015
DOI: 10.7907/Z9CC0XMN
Since the discovery of the Higgs boson at the LHC, its use as a probe to search for beyond the standard model physics, such as supersymmetry, has become important, as seen in a recent search by the CMS experiment using razor variables in the diphoton final state. Motivated by this search, this thesis examines the LHC discovery potential of a SUSY scenario involving bottom squark pair production with a Higgs boson in the final state. We design and implement a software-based trigger using the razor variables for the CMS experiment to record events with a bottom quark-antiquark pair from a Higgs boson. We characterize the full range of signatures at the LHC from this Higgs-aware SUSY scenario and demonstrate the sensitivity of the CMS data to this model.
https://thesis.library.caltech.edu/id/eprint/9535Nanofabrication for On-Chip Optical Levitation, Atom-Trapping, and Superconducting Quantum Circuits
https://resolver.caltech.edu/CaltechTHESIS:10292014-120111728
Authors: {'items': [{'email': 'gugooju@gmail.com', 'id': 'Norte-Richard-Alexander', 'name': {'family': 'Norte', 'given': 'Richard Alexander'}, 'show_email': 'YES'}]}
Year: 2015
DOI: 10.7907/Z9WS8R61
Researchers have spent decades refining and improving their methods for fabricating smaller, finer-tuned, higher-quality nanoscale optical elements with the goal of making more sensitive and accurate measurements of the world around them using optics. Quantum optics has been a well-established tool of choice in making these increasingly sensitive measurements which have repeatedly pushed the limits on the accuracy of measurement set forth by quantum mechanics. A recent development in quantum optics has been a creative integration of robust, high-quality, and well-established macroscopic experimental systems with highly-engineerable <i>on-chip</i> nanoscale oscillators fabricated in cleanrooms. However, merging large systems with nanoscale oscillators often require them to have extremely high aspect-ratios, which make them extremely delicate and difficult to fabricate with an "experimentally reasonable" repeatability, yield and high quality. In this work we give an overview of our research, which focused on microscopic oscillators which are coupled with macroscopic optical cavities towards the goal of cooling them to their motional ground state in room temperature environments. The quality factor of a mechanical resonator is an important figure of merit for various sensing applications and observing quantum behavior. We demonstrated a technique for pushing the quality factor of a micromechanical resonator beyond conventional material and fabrication limits by using an optical field to stiffen and trap a particular motional mode of a nanoscale oscillator. Optical forces increase the oscillation frequency by storing most of the mechanical energy in a nearly loss-less optical potential, thereby strongly diluting the effects of material dissipation. By placing a 130 nm thick SiO<sub>2</sub> pendulum in an optical standing wave, we achieve an increase in the pendulum center-of-mass frequency from 6.2 to 145 kHz. The corresponding quality factor increases 50-fold from its intrinsic value to a final value of Q<sub>m</sub> = 5.8(1.1) x 10<sup>5</sup>, representing more than an order of magnitude improvement over the conventional limits of SiO<sub>2</sub> for a pendulum geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems. We then give a detailed overview of the techniques used to produce high-aspect-ratio nanostructures with applications in a wide range of quantum optics experiments. The ability to fabricate such nanodevices with high precision opens the door to a vast array of experiments which integrate macroscopic optical setups with lithographically engineered nanodevices. Coupled with atom-trapping experiments in the Kimble Lab, we use these techniques to realize a new waveguide chip designed to address ultra-cold atoms along lithographically patterned nanobeams which have large atom-photon coupling and near 4π Steradian optical access for cooling and trapping atoms. We describe a fully integrated and scalable design where cold atoms are spatially overlapped with the nanostring cavities in order to observe a resonant optical depth of d<sub>0</sub> ≈ 0.15. The nanodevice illuminates new possibilities for integrating atoms into photonic circuits and engineering quantum states of atoms and light on a microscopic scale. We then describe our work with superconducting microwave resonators coupled to a phononic cavity towards the goal of building an integrated device for quantum-limited microwave-to-optical wavelength conversion. We give an overview of our characterizations of several types of substrates for fabricating a low-loss high-frequency electromechanical system. We describe our electromechanical system fabricated on a Si<sub>3</sub>N<sub>4</sub> membrane which consists of a 12 GHz superconducting LC resonator coupled capacitively to the high frequency localized modes of a phononic nanobeam. Using our suspended membrane geometry we isolate our system from substrates with significant loss tangents, drastically reducing the parasitic capacitance of our superconducting circuit to ≈ 2.5$ fF. This opens up a number of possibilities in making a new class of low-loss high-frequency electromechanics with relatively large electromechanical coupling. We present our substrate studies, fabrication methods, and device characterization.https://thesis.library.caltech.edu/id/eprint/8718Dynamic Characterization of Micro-Particle Systems
https://resolver.caltech.edu/CaltechTHESIS:07082015-183754265
Authors: {'items': [{'email': 'wei.xun.lin@gmail.com', 'id': 'Lin-Wei-Hsun', 'name': {'family': 'Lin', 'given': 'Wei-Hsun'}, 'show_email': 'YES'}]}
Year: 2016
DOI: 10.7907/Z9D798BJ
<p>Ordered granular systems have been a subject of active research for decades. Due to their rich dynamic response and nonlinearity, ordered granular systems have been suggested for several applications, such as solitary wave focusing, acoustic signals manipulation, and vibration absorption. Most of the fundamental research performed on ordered granular systems has focused on macro-scale examples. However, most engineering applications require these systems to operate at much smaller scales. Very little is known about the response of micro-scale granular systems, primarily because of the difficulties in realizing reliable and quantitative experiments, which originate from the discrete nature of granular materials and their highly nonlinear inter-particle contact forces.</p>
<p>In this work, we investigate the physics of ordered micro-granular systems by designing an innovative experimental platform that allows us to assemble, excite, and characterize ordered micro-granular systems. This new experimental platform employs a laser system to deliver impulses with controlled momentum and incorporates non-contact measurement apparatuses to detect the particles’ displacement and velocity. We demonstrated the capability of the laser system to excite systems of dry (stainless steel particles of radius 150 micrometers) and wet (silica particles of radius 3.69 micrometers, immersed in fluid) micro-particles, after which we analyzed the stress propagation through these systems.</p>
<p>We derived the equations of motion governing the dynamic response of dry and wet particles on a substrate, which we then validated in experiments. We then measured the losses in these systems and characterized the collision and friction between two micro-particles. We studied wave propagation in one-dimensional dry chains of micro-particles as well as in two-dimensional colloidal systems immersed in fluid. We investigated the influence of defects to wave propagation in the one-dimensional systems. Finally, we characterized the wave-attenuation and its relation to the viscosity of the surrounding fluid and performed computer simulations to establish a model that captures the observed response.</p>
<p>The findings of the study offer the first systematic experimental and numerical analysis of wave propagation through ordered systems of micro-particles. The experimental system designed in this work provides the necessary tools for further fundamental studies of wave propagation in both granular and colloidal systems.</p>https://thesis.library.caltech.edu/id/eprint/9054Thermopower in Two-Dimensional Electron Systems
https://resolver.caltech.edu/CaltechTHESIS:12122015-165527858
Authors: {'items': [{'email': 'chickering.bill@gmail.com', 'id': 'Chickering-William-Elbridge', 'name': {'family': 'Chickering', 'given': 'William Elbridge'}, 'show_email': 'YES'}]}
Year: 2016
DOI: 10.7907/Z9HT2M7G
<p>The subject of this thesis is the measurement and interpretation of thermopower in high-mobility two-dimensional electron systems (2DESs). These 2DESs are realized within state-of-the-art GaAs/AlGaAs heterostructures that are cooled to temperatures as low as T = 20 mK. Much of this work takes place within strong magnetic fields where the single-particle density of states quantizes into discrete Landau levels (LLs), a regime best known for the quantum Hall effect (QHE). In addition, we review a novel hot-electron technique for measuring thermopower of 2DESs that dramatically reduces the influence of phonon drag.</p>
<p>Early chapters concentrate on experimental materials and methods. A brief overview of GaAs/AlGaAs heterostructures and device fabrication is followed by details of our cryogenic setup. Next, we provide a primer on thermopower that focuses on 2DESs at low temperatures. We then review our experimental devices, temperature calibration methods, as well as measurement circuits and protocols.</p>
<p>Latter chapters focus on the physics and thermopower results in the QHE regime. After reviewing the basic phenomena associated with the QHE, we discuss thermopower in this regime. Emphasis is given to the relationship between diffusion thermopower and entropy. Experimental results demonstrate this relationship persists well into the fractional quantum Hall (FQH) regime.</p>
<p>Several experimental results are reviewed. Unprecedented observations of the diffusion thermopower of a high-mobility 2DES at temperatures as high as T = 2 K are achieved using our hot-electron technique. The composite fermion (CF) effective mass is extracted from measurements of thermopower at LL filling factor ν = 3/2. The thermopower versus magnetic field in the FQH regime is shown to be qualitatively consistent with a simple entropic model of CFs. The thermopower at ν = 5/2 is shown to be quantitatively consistent with the presence of non-Abelian anyons. An abrupt collapse of thermopower is observed at the onset of the reentrant integer quantum Hall effect (RIQHE). And the thermopower at temperatures just above the RIQHE transition suggests the existence of an unconventional conducting phase.</p>https://thesis.library.caltech.edu/id/eprint/9320Fundamentals of Thermocapillary Sculpting of Liquid Nanofilms and Applications to Thin Film Micro-Optics
https://resolver.caltech.edu/CaltechTHESIS:03062017-120100812
Authors: {'items': [{'email': 'fiedlekr@gmail.com', 'id': 'Fiedler-Kevin-Robert', 'name': {'family': 'Fiedler', 'given': 'Kevin Robert'}, 'orcid': '0000-0002-9656-7663', 'show_email': 'YES'}]}
Year: 2017
DOI: 10.7907/Z92J68X1
<p>This doctoral thesis describes experimental work conducted as part of ongoing efforts to identify and understand the source of linear instability in ultrathin liquid films subject to large variations in surface temperature along the air/liquid interface. Previous theoretical efforts by various groups have identified three possible physical mechanisms for instability, including an induced surface charge model, an acoustic phonon model, and a thermocapillary model. The observed instability manifests as the spontaneous formation of arrays of nano/microscale liquid protrusions arising from an initially flat nanofilm, whose organization is characterized by a distinct in-plane wavelength and associated out-of-plane growth rate. Although long range order is somewhat difficult to achieve due to thin film defects incurred during preparation, the instability tends toward hexagonal symmetry within periodic domains achieved for a geometry in which the nanofilm is held in close proximity to a cooled, proximate, parallel, and featureless substrate.</p>
<p>In this work, data obtained from a previous experimental setup is analyzed and it is shown how key improvements in image processing and analysis, coupled with more accurate finite element simulations of thermal profiles, lead to more accurate identification of the fastest growing unstable mode at early times. This fastest growing mode is governed by linear instability and exponential growth. This work was followed by re-examination of real time interference fringes using differential colorimetry to quantify the actual rate of growth of the fastest growing peaks within the protrusion arrays. These initial studies and lingering questions led to the introduction of a new and improved experimental setup, which was redesigned to yield larger and more reproducible data sets. Corresponding improvements to the image analysis process allowed for the measurement of both the wavelength and growth rate of the fastest growing mode simultaneously. These combined efforts establish that the dominant source of instability is attributable to large thermocapillary stresses. For the geometry in which the nanofilm surface is held in close proximity to a cooled and parallel substrate, the instability leads to a runaway process, characterized by exponential growth, in which the film is attracted to the cooled target until contact is achieved.</p>
<p>The second part of this thesis describes fabrication and characterization of microlens arrays and linear waveguide structures using a similar experimental setup. However, instead of relying on the native instability observed, formation and growth of liquid shapes and protrusions is triggered by pre-patterning the cooled substrate with a desired mask for replication. These preformed cooled patterns, held in close proximity to an initially flat liquid nanofilm, induce a strong non-linear response via consequent patterned thermocapillary stresses imposed along the air/liquid interface. Once the desired film shapes are achieved, the transverse thermal gradient is removed and the micro-optical components are affixed in place naturally by the resultant rapid solidification. The use of polymer nanofilms with low glass transition temperatures, such as polystyrene, facilitated rapid solidification, while providing good optical response. Surface characterization of the resulting micro-optical components was accomplished by scanning white light interferometry, which evidences formation of ultrasmooth surfaces ideal for optical applications. Finally, linear waveguides were created by this thermocapillary sculpting technique and their optical performance characterized. In conclusion, these measurements highlight the true source of instability in this geometry, and the fabrication demonstrations pave the way for harnessing this knowledge for the design and creation of novel micro-optical devices.</p>https://thesis.library.caltech.edu/id/eprint/10087Investigating Quantum Speedups through Numerical Simulations
https://resolver.caltech.edu/CaltechTHESIS:06052017-122137777
Authors: {'items': [{'email': 'shannonawang@yahoo.com', 'id': 'Wang-Shannon', 'name': {'family': 'Wang', 'given': 'Shannon'}, 'orcid': '0000-0003-0585-6556', 'show_email': 'YES'}]}
Year: 2017
DOI: 10.7907/Z9ZP4456
It has been recently noted in a paper by Brandao et al. that the structure of a linear program in a classical semidefinite programming algorithm lends itself to quantization, such that the classical algorithm may experience a quantum speedup if the step of solving a linear program is replaced with the preparation of a Gibbs state of classical Hamiltonian on a quantum computer, where the Hamiltonian is given by a linear combination of the semidefinite program's constraint matrices. The quantum speedup would be exponential if the complexity of the Gibbs sampler used to execute the update step is polynomial in system size. The Gibbs samplers with explicitly defined runtimes are exponential in system size; however, while the quantum Metropolis sampling algorithm by Temme et al. does not have a runtime bounded explicitly in system size, the algorithm heuristically runs in polylogarithmic time. Since the inverse spectral gap of the quantum Metropolis map varies inversely with the running time of the algorithm, we simulate the behavior of the quantum Metropolis map's spectral gap as a function of system size and row sparsity. We also examine how different definitions of fixed row sparsity affect the spectral gap's behavior when the system size is increased linearly. While more numerical evidence is needed to draw a definitive conclusion, the current results appear to indicate that for system sizes ranging from three to ten qubits, if fixed row sparsity is defined as a fixed polynomial function of the system size, then the quantum Metropolis spectral gap behaves as a polynomial function of system size.https://thesis.library.caltech.edu/id/eprint/10282A System for Cancellation of Two-Level System Noise in Kinetic Inductance Devices
https://resolver.caltech.edu/CaltechTHESIS:01282022-221737571
Authors: {'items': [{'email': 'alex.meiburg@gmail.com', 'id': 'Meiburg-Alexander-Heinz', 'name': {'family': 'Meiburg', 'given': 'Alexander'}, 'orcid': '0000-0002-4506-9146', 'show_email': 'YES'}]}
Year: 2018
DOI: 10.7907/372p-e428
Kinetic Inductance Detectors (KIDs) are showing promise in a variety of low-light applications photometry applications, notably in observing B-mode polarization of the cosmic microwave background. These devices are read out by modulating the inductance of an LC resonator through light, and observing the shift in resonant frequency. Among several contributing sources of noise is Two-Level System noise (TLS noise) that causes low-loss drift in the frequency. Under certain assumptions of the source of the noise, we propose a new dual-resonator design that would allow the TLS noise to be observed independently of the signal, and thus cancelled out. This design comes at a roughly factor-of-2 cost in component size and sensitivity. We designed a manufactured a niobium-on-silicon chip, but encountered issues in that we were unable to observe enough TLS noise to conclusively say that the cancellation works.https://thesis.library.caltech.edu/id/eprint/14486Search for SUSY with Delayed Photons at the Compact Muon Solenoid
https://resolver.caltech.edu/CaltechTHESIS:05222018-110636485
Authors: {'items': [{'email': 'gillian.kopp@gmail.com', 'id': 'Kopp-Gillian-Baron', 'name': {'family': 'Kopp', 'given': 'Gillian Baron'}, 'orcid': '0000-0001-8160-0208', 'show_email': 'NO'}]}
Year: 2018
DOI: 10.7907/G4D7-G385
The Compact Muon Solenoid (CMS) experiment records data from proton-proton (pp) and heavy ion (Pb-Pb and Pb-p) collisions at the Large Hadron Collider (LHC) to search for physics beyond the Standard Model, test theories of supersymmetry (SUSY), and measure properties of known particles with higher precision. In 2025, the LHC will be upgraded to the High Luminosity LHC (HL-LHC), where the luminosity will be increased by a factor of 10. This will increase the number of pile-up collisions to 140-200 events per proton-proton bunch crossing, compared to the current 40 events per crossing (where each bunch crossing occurs every 25 ns). In order to fully exploit the sensitivity of the CMS experiment, the current detectors must be upgraded to mitigate the effects of the large number of pileup interactions expected in collisions at the HL-LHC. New capabilities, such as precision timing measurements in calorimetric devices and minimum ionizing detectors, have been shown to effectively mitigate the effects due to pileup, and are expected to benefit the overall physics reach of the experiment. In addition to mitigating pileup and increasing the detector capabilities, precision timing is beneficial in the search for particles beyond the Standard Model. A simulation of a benchmark long lived neutralino SUSY search is presented, and it is shown that the generator particle flight times can be faithfully reconstructed using the detector-level information. Identification algorithms for the SUSY model have been significantly improved with the use of a Boosted Decision Tree, and it is demonstrated that this algorithm has many benefits as compared to cut based IDs. With use of the BDT for the long lived neutralino SUSY model, the background rejection is increased significantly, with constant signal acceptance of 53.6%. This is an improvement in the significance of the signal selection by a factor of 2.38. Further improvement is seen with the inclusion of detector timing information in the BDT – with this contributing ≈25% of the information used in signal event identification. We thus demonstrate that with the BDT, the SUSY neutralino search can be performed with increased signal identification significance, and the searches’ sensitivity is expected to improve with the time resolution attained by the upgraded CMS calorimeter. https://thesis.library.caltech.edu/id/eprint/10924Characterization and Improvement of the Thermal Stability of TES Bolometers
https://resolver.caltech.edu/CaltechTHESIS:07182018-144446266
Authors: {'items': [{'email': 'rfsonka@gmail.com', 'id': 'Sonka-Rita-Frances', 'name': {'family': 'Sonka', 'given': 'Rita Frances'}, 'orcid': '0000-0002-1187-9781', 'show_email': 'NO'}]}
Year: 2018
DOI: 10.7907/4v3d-7k67
<p>The successful detection and characterization of the B-modes in the Cosmic Microwave Background (CMB) would dramatically illuminate the physics of the inflationary era. The Observational Cosmology Group is iterating on bolometers in an attempt to detect this signal. The previous detector design became unstable in parts of its transition when adjusted for 220/270 GHz frequencies, limiting its use.</p>
<p>We study the mechanism of instability in these transition edge sensor (TES) bolometers used for ground based observations of the Cosmic Microwave Background (CMB) at 270GHz. The instability limits the range of useful operating resistances of the TES down to ≈50% of the TES normal resistance (R_n), and due to variations in detector properties and optical loading within a column of multiplexed detectors, limits the effective on sky yield to ≈67 %.</p>
<p>Through comparison of 7 new detector thermal capacity designs and measurements of the electrical impedance of the detectors, we show the instability is due to the increased bolometer leg G for higher-frequency detection inducing decoupling of the palladium-gold heat capacity from the thermistor. We demonstrate experimentally that the limiting thermal resistance is due to the small cross sectional area of the silicon nitride bolometer island, and so is easily fixed by layering palladium-gold over an oxide protected TES. The resulting detectors can be biased down to a resistance ≈10% of R<sub>n</sub>, improving the effective on-sky yield to ≈93%.</p>
<p>We also investigate a possibly related, unexpected slope in the Aluminum calibration TES transition and determine that it is not due to phase separation, even accounting for the science TES thermal instability.</p>
https://thesis.library.caltech.edu/id/eprint/11125Towards High Fidelity Quantum Computation and Simulation with Rydberg Atoms
https://resolver.caltech.edu/CaltechTHESIS:06092020-162351992
Authors: {'items': [{'email': 'anantkale711@gmail.com', 'id': 'Kae-Anant-M', 'name': {'family': 'Kale', 'given': 'Anant M.'}, 'orcid': '0000-0002-7049-5630', 'show_email': 'YES'}]}
Year: 2020
DOI: 10.7907/8mee-md98
Individually trapped neutral atoms are a promising candidate for use in quantum computing and simulation applications. They are highly scalable, have long coherence times and can be entangled via strong dipole-dipole interactions by driving to highly excited Rydberg states. However, the fidelity of single atom operations as well as two-atom entangling operations is limited by intrinsic sources of decoherence such as atomic motion, as well as technical sources of noise such as laser intensity fluctuations and phase/frequency fluctuations. We study the effect of these factors on single atom Rabi oscillations and two-atom Rydberg blockaded Rabi oscillations, using perturbation theory and numerical simulation. We develop a window function approach which helps us qualitatively understand the significance of the different spectral components of the noise as well as quantitatively understand the dependence of the Rabi oscillation fidelity on Rabi frequency. This allows us to predict the maximum experimentally achievable fidelities using independent measurements of experimental parameters such as noise spectra and atomic temperature. Turning to the question of near-term scalability of the experimental system, we prototype and test a method of generating a ’ladder’ configuration of optical tweezers utilizing two independent lasers. Our setup allows us to fully tune the geometry of the ladder, namely the separation between the two rows, the angle between them, and their relative position along the axis of the ladder. This pseudo-2D configuration enables us to reach larger system sizes in the near future and allows us to access beyond 1D physics.https://thesis.library.caltech.edu/id/eprint/13812Gravitational Wave Polarizations: A Test of General Relativity Using Binary Black Hole Mergers
https://resolver.caltech.edu/CaltechTHESIS:08062020-222003579
Authors: {'items': [{'email': 'mathur26sudhi@gmail.com', 'id': 'Mathur-Sudhi', 'name': {'family': 'Mathur', 'given': 'Sudhi'}, 'orcid': '0000-0003-4891-0567', 'show_email': 'NO'}]}
Year: 2020
DOI: 10.7907/q9qa-7770
<p>General Relativity predicts that gravitational radiation is purely tensor polarized and thus, gravitational waves are composed of linear combinations of two transverse polarization modes, referred to as plus (+) and cross (×) tensor modes. However, alternate gravitational theories predict the existence of up to four additional vector and scalar longitudinal GW polarization modes.</p>
<p>In this thesis, we develop a test of the gravitational wave (GW) polarization prediction of general relativity by searching for small admixtures of vector and/or scalar polarization components in transient GWs from binary black hole mergers. We use a network of five non-co-oriented GW detectors available in the near future, Bayesian inference parameter estimation, and nested sampling to quantify the detection sensitivity for such non-tensor GW polarization components.</p>https://thesis.library.caltech.edu/id/eprint/13851Using Graviton EFT and Massive Gravity to Compute Gravitational Potentials for Black Hole Inspirals
https://resolver.caltech.edu/CaltechTHESIS:10212021-181920642
Authors: {'items': [{'email': 'bethanysuter42@gmail.com', 'id': 'Suter-Bethany-Anne', 'name': {'family': 'Suter', 'given': 'Bethany Anne'}, 'orcid': '0000-0002-4503-5771', 'show_email': 'YES'}]}
Year: 2020
DOI: 10.7907/jh6b-bt24
This year, the LIGO detectors entered their third observing run and have been detecting black hole interactions with increasing precision and sensitivity. These detections have opened up a new way to compare the predictions of Einsteinian gravity with more exotic models. One of these models, massive gravity, is a concrete toy to use in testing these predictions. This project uses ideas from EFT and standard techniques from quantum field theory to calculate scattering amplitudes for scalar particles interacting via gravitons. We first calculated amplitudes up to the 1-looplevel assuming the standard massless graviton and then assuming a massive graviton. We then mapped these amplitudes to gravitational potentials for black holes. Future work will include looking at the different predictions of these two theories (massless and massive gravitons), and comparing them to black hole inspiral data to determine if the massive graviton theory could be a legitimate contender as a model for gravity.https://thesis.library.caltech.edu/id/eprint/14404The Limits of The Quasi-Harmonic Approximation: Anharmonicity in Germanium and the Entropy of Melting
https://resolver.caltech.edu/CaltechTHESIS:12012021-011312125
Authors: {'items': [{'email': 'shivamudide628@gmail.com', 'id': 'Mudide-Shiva', 'name': {'family': 'Mudide', 'given': 'Shiva'}, 'show_email': 'YES'}]}
Year: 2021
DOI: 10.7907/9mn0-y471
<p>Inelastic Neutron Scattering (INS) measurements were made at the Wide Angular-Range Chopper Spectrometer (ARCS) on Germanium at temperatures higher than what has been done before, from 296 K to 1203 K. Raw data was used to calculate the dynamic structure factor. Multi-phonon and multiple scattering events were accounted for and subtracted. These dynamic structure factors were then used to calculate single phonon density of states (DOS) for temperatures throughout the said temperature range. Thermal softening of the phonon modes was observed. The softening was quantitatively characterized with several Gruneisen parameters to better understand the effects phonon anharmonicity in Germanium. We find the quasi-harmonic approximation alone cannot explain the large phonon softening. The vibrational entropy contribution to the total entropy was also determined. We find that the vibrational entropy makes up almost all of the total entropy in Germanium, even at elevated temperatures.</p>
<p>We also conduct melting experiments to ensure containment of Si, Bi, and Pb in quartz ampules. These metals will be heated through their melting points at ARCS in the near future in order to determine the vibrational entropy contribution to the latent heat of melting. Furthermore, we write an algorithm based on the work of Sivia to determine the number of phonon modes there is the maximum evidence for in any given phonon DOS.</p>https://thesis.library.caltech.edu/id/eprint/14438Quantum Computing for Machine Learning and Physics Simulation
https://resolver.caltech.edu/CaltechTHESIS:09272022-143825909
Authors: {'items': [{'email': 'azlokapa@mit.edu', 'id': 'Zlokapa-Alexander', 'name': {'family': 'Zlokapa', 'given': 'Alexander'}, 'orcid': '0000-0002-4153-8646', 'show_email': 'NO'}]}
Year: 2021
DOI: 10.7907/q75q-zm20
<p>Quantum computing is widely thought to provide exponential speedups over classical algorithms for a variety of computational tasks. In classical computing, methods in artificial intelligence such as neural networks and adversarial learning have enabled drastic improvements in state-of-the-art performance for a variety of tasks. We consider the intersection of quantum computing with machine learning, including the quantum algorithms for deep learning on classical datasets, quantum adversarial learning for quantum states, and variational quantum machine learning for improved physics simulation.</p>
<p>We consider a standard deep neural network architecture and show that conditions amenable to trainability by gradient descent coincide with those necessary for an efficient quantum algorithm. Considering the neural network in the infinite-width limit using the neural tangent kernel formalism, we propose a quantum algorithm to train the neural network with vanishing error as the training dataset size increases. Under a sparse approximation of the neural tangent kernel, the training time scales logarithmically with the number of training examples, providing the first known exponential quantum speedup for feedforward neural networks. Related approximations to the neural tangent kernel are discussed, with numerical studies showing successful convergence beyond the proven regime. Our work suggests the applicability of the quantum computing to additional neural network architectures and common datasets such as MNIST, as well as kernel methods beyond the neural tangent kernel.</p>
<p>Generative adversarial networks (GANs) are one of the most widely adopted machine learning methods for data generation. We propose an entangling quantum GAN (EQ-GAN) that overcomes some limitations of previously proposed quantum GANs. EQ-GAN guarantees the convergence to a Nash equilibrium under minimax optimization of the discriminator and generator circuits by performing entangling operations between both the generator output and true quantum data. We show that EQ-GAN has additional robustness against coherent errors and demonstrate the effectiveness of EQ-GAN experimentally in a Google Sycamore superconducting quantum processor. By adversarially learning efficient representations of quantum states, we prepare an approximate quantum random access memory and demonstrate its use in applications including the training of near-term quantum neural networks.</p>
<p>With quantum computers providing a natural platform for physics simulation, we investigate the use of variational quantum circuits to simulate many-body systems with high fidelity in the near future. In particular, recent work shows that teleportation caused by introducing a weak coupling between two entangled SYK models is dual to a particle traversing an AdS-Schwarzschild wormhole, providing a mechanism to probe quantum gravity theories in the lab. To simulate such a system, we propose the process of compressed Trotterization to improve the fidelity of time evolution on noisy devices. The task of learning approximate time evolution circuits is shown to have a favorable training landscape, and numerical experiments demonstrate its relevance to simulating other many-body systems such as a Fermi-Hubbard model. For the SYK model in particular, we demonstrate the construction of a low-rank approximation that favors a shallower Trotterization. Finally, classical simulations of finite-N SYK models suggest that teleportation via a traversable wormhole instead of random unitary scrambling is achievable with O(20) qubits, providing further indication that such quantum gravity experiments may realizable with near-term quantum hardware.</p>https://thesis.library.caltech.edu/id/eprint/15035Liquid-Induced Discharge of Polypropylene Microfiber Electret Filters
https://resolver.caltech.edu/CaltechTHESIS:06162021-230506010
Authors: {'items': [{'email': 'albertnazeeri@gmail.com', 'id': 'Nazeeri-Albert-Isaac', 'name': {'family': 'Nazeeri', 'given': 'Albert Isaac'}, 'orcid': '0000-0003-0000-9841', 'show_email': 'YES'}]}
Year: 2021
DOI: 10.7907/f88b-x760
<p>Polymer microfiber electret filters are the technology behind N95 and equivalent type respirators. Understanding how liquids interact with and discharge these filters would allow for the development of non-damaging liquid decontamination protocols. Previous work on liquid/filter interactions has been largely empirical with articles reporting the effect a specific liquid has on the filtration efficiency of a particular filter. This thesis proposes a theoretical model of liquid induced discharge of polymer microfiber electret filters via the ideas of surface wetting and electrical conductivity. This model was tested, and validated, on commercially available polypropylene microfiber electret filters through wetting, thermally stimulated discharge (TSD), and filtration experiments.</p>https://thesis.library.caltech.edu/id/eprint/14279Direct Imaging of Exoplanets Closer to Stars
https://resolver.caltech.edu/CaltechTHESIS:06192022-010740124
Authors: {'items': [{'email': 'shubhagrawal30@gmail.com', 'id': 'Agrawal-Shubh', 'name': {'family': 'Agrawal', 'given': 'Shubh'}, 'orcid': '0000-0003-2429-5811', 'show_email': 'YES'}]}
Year: 2022
DOI: 10.7907/17sv-vf40
<p>Detecting exoplanets through direct imaging at lower angular separations, where more planets are expected to be, is limited by the variability of the stellar point spread function. Integral field spectrographs like OSIRIS at the Keck Observatory can leverage high spectral resolution to search for new planets at smaller separations (< 0.3 arcseconds) by detecting their distinct spectral signature compared to the diffracted starlight. In this thesis, we present the mid-survey results of a search for planets around 23 targets in the Ophiuchus and Taurus star-forming regions.</p>
<p>We use this pathfinder survey with Keck/OSIRIS to demonstrate our technique and compare the final sensitivities to other classical imaging techniques, particularly at separations of 0.05-0.3 arcseconds. We detect an M dwarf companion around HD 148352 at a ≈ 34<i>σ</i> significance level. We measure this binary star companion to be at an angular separation of roughly $0.11$ milliarcseconds, with a contrast of $0.38\%$, effective temperature <i>T</i><sub>eff</sub> ≈ 3200 K, and radial velocity <i>RV</i> ≈ 12 km/s. We also present other low-significance objects, along with detection maps and sensitivity limits around these 23 targets.</p>
<p>We use our open-source data analysis pipeline, called the Broad Repository for Exoplanet Analysis, Detection, and Spectroscopy (breads), as the framework for this planet search. breads operates on high spectral resolution data from existing and in-development instruments. Our code is based on a forward-modeling framework, which is statistically more accurate than classical cross-correlation techniques. It includes a built-in optimization and analytical marginalization of linear parameters in the forward model, therefore limiting the number of parameters to be explored by the posterior sampling method. We allow users to select forward models, parameters to detect and analyze, and fitting methods like Markov Chain Monte Carlo sampling, grid optimization, and gradient descent. breads provides a flexible framework to retrieve radial velocity, spin, and atmospheric parameters of high-contrast companions. We also describe wavelength and resolution calibration, transmission and spectra calculation, and bad pixel identification techniques.</p>
<p>Our work will be applicable to future integral field spectrographs like NIRSpec on the James Webb Space Telescope and other first light instruments on the future Extremely Large Telescopes, which are poised to become the next generation of exoplanet detection facilities.</p>https://thesis.library.caltech.edu/id/eprint/14962Transient Behavior of Granular Material
https://resolver.caltech.edu/CaltechTHESIS:06012023-222631854
Authors: {'items': [{'email': 'ic64133@gmail.com', 'id': 'Lin-Han-Hsin', 'name': {'family': 'Lin', 'given': 'Han-Hsin'}, 'orcid': '0009-0003-8640-470X', 'show_email': 'NO'}]}
Year: 2023
DOI: 10.7907/jjrv-x616
<p>This PhD thesis focuses on the flows on granular materials, such as sand, glass beads, and powders, which are sheared at low speeds with gravity perpendicular to the flow direction. The study is conducted using a combination of experiments, simulations, and theory, with the goal of developing a unifying theory of granular materials that can be described by continuum models. The main objective is to understand how microscale physics propagate to macroscale phenomena and to address issues related to setting boundary conditions and predicting timescales from unsteady to steady states. This research primarily aims to investigate stress variations in granular materials as a function of shear rate, encompassing both steady and unsteady states. Additionally, the thesis examines the phenomena of wall force anomalies and vortex flows. In Couette cell experiments and vertical plane shear simulations, granular material demonstrates a downward flow near the vertical shearing wall and an upward flow adjacent to another static vertical wall. Interestingly, this vortex flow causes a change in the direction of vertical shear stress when wall shearing commences, contradicting the prevalent assumption that particles consistently apply a downward force on the vertical wall.</p>
<p>The study concludes with key findings, including the observation that normal and shear stresses on the shearing wall increase slowly after the initiation of shearing, and that steady-state values for these stresses are independent of the shearing speed within a certain range. The study also found that the height of particles near the shearing wall decreases gradually with the presence of vortex flow, and that the shear rate near the moving wall is initially high and decreases slowly to reach a steady state. Additionally, we used a non-local constitutive model and Boussinesq approximation to predict the downward flow that is driven by gravity and variations in the solid fraction near the shearing surface, as well as the decay profile of velocity in an infinitely wide box for the steady state.</p>
<p>Overall, this thesis contributes to our understanding of granular materials in the slow flow regime, providing insights into their behavior under shear. The non-local model accurately predicts the downward flow and velocity decay profile, indicating its potential as a valuable tool for future research.</p>https://thesis.library.caltech.edu/id/eprint/15267A Deep Dive into the Connections Between the Renormalization Group and Deep Learning in the Ising Model
https://resolver.caltech.edu/CaltechTHESIS:05302023-084739008
Authors: {'items': [{'email': 'kelsietaylor137@gmail.com', 'id': 'Taylor-Kelsie-Reed', 'name': {'family': 'Taylor', 'given': 'Kelsie'}, 'orcid': '0009-0001-7510-2306', 'show_email': 'YES'}]}
Year: 2023
DOI: 10.7907/ztpg-z092
The renormalization group (RG) is an essential technique in statistical physics and quantum field theory, which considers scale-invariant properties of physical theories and how these theories’ parameters change with scaling. Deep learning is a powerful computational technique that uses multi-layered neural networks to solve a myriad of complicated problems. Previous research suggests the possibility that unsupervised deep learning may be a form of RG flow, by being a layer-by-layer coarse graining of the original data. We examined this connection on a more rigorous basis for the simple example of Kadanoff block renormalization of the 2D nearest-neighbor Ising model, with our deep learning accomplished via Restricted Boltzmann Machines (RBMs). We developed extensive renormalization techniques for the 1D and 2D Ising model to provide a baseline for comparison. For the 1D Ising model, we successfully used Adam optimization on a correlation length loss function to learn the group flow; yielding results consistent with the analytical model for infinite N. For the 2D Ising model, we successfully generated Ising model samples using the Wolff algorithm, and performed the group flow using a quasi-deterministic method, validating these results by calculating the critical exponent \nu. We then examined RBM learning of the Ising model layer by layer, finding a blocking structure in the learning that is qualitatively similar to RG. Lastly, we directly compared the weights of each layer from the learning to Ising spin renormalization, but found quantitative inconsistencies for the simple case of nearest-neighbor Ising models.https://thesis.library.caltech.edu/id/eprint/15230