CaltechAUTHORS: Combined
https://feeds.library.caltech.edu/people/Schwab-K-C/combined.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 21 May 2024 19:48:31 -0700Fabrication of a silicon-based superfluid oscillator
https://resolver.caltech.edu/CaltechAUTHORS:20160606-154551314
Year: 1996
DOI: 10.1109/84.536624
We have constructed an integrated superfluid oscillator using various silicon processing techniques, including micromachining and electron beam lithography. This device has the advantage of a very small internal volume (0.72 mm^3). This makes it insensitive to spurious external acoustic noise which has limited the performance of larger experiments. We have tested the performance of this device in two configurations, one with a single micro-aperture and another with an additional fine tube. Both configurations demonstrate macroscopic quantum phenomena in superfluid ^4He at low temperatures (0.25 K < T <2.2 K) and have been used to study these effects in detail.https://resolver.caltech.edu/CaltechAUTHORS:20160606-154551314Phase-slip memory effects in dissipation-free superflow
https://resolver.caltech.edu/CaltechAUTHORS:20160606-155537072
Year: 1997
DOI: 10.1103/PhysRevB.55.8094
Critical superflow, preceding a free ringing superfluid oscillation, induces a remnant stochastic uncertainty in the oscillation amplitude. We demonstrate that the distribution function for the oscillation's velocity amplitude reflects both the quantized size of the underlying phase-slip dissipation events, as well as the stochastic nature of the processes which nucleate the slips.https://resolver.caltech.edu/CaltechAUTHORS:20160606-155537072Detection of the Earth's rotation using superfluid phase coherence
https://resolver.caltech.edu/CaltechAUTHORS:20160606-160028066
Year: 1997
DOI: 10.1038/386585a0
It has long been recognized that the macroscopic quantum properties of superfluid helium could form the basis of a technique for measuring the state of absolute rotation of the containment vessel: circulation of superfluid helium is quantized, so providing a reference state of zero rotation with respect to inertial space. Here we provide experimental proof of this concept by detecting the rotation of the Earth using the spatial phase coherence of superfluid ^4He, thus providing independent corroboration of an earlier report that demonstrated the feasibility of making such a measurement. Our superfluid container is constructed on a centimetre-size silicon wafer, and has an essentially toroidal geometry but with the flow path interrupted by partition incorporating a sub-micrometre aperture. Rotation of the container induces a measurable flow velocity through the aperture in order to maintain coherence in the quantum phase of the super-fluid. Using this device, we determine the Earth's rotation rate to a precision of 0.5% with a measurement time of one hour, and argue that improvements in sensitivity of several orders of magnitude should be feasible.https://resolver.caltech.edu/CaltechAUTHORS:20160606-160028066Thermoviscous effects in steady and oscillating flow of superfluid ^4He: Experiments
https://resolver.caltech.edu/CaltechAUTHORS:20160523-151326888
Year: 1997
DOI: 10.1007/BF02396910
The correct interpretation of superfluid flow experiments relies on the knowledge of thermal and viscous effects that can cause deviations from ideal behavior. The previous paper presented a theoretical study of dissipative and reactive(nondissipative) thermoviscous effects in both steady and oscillating flow of an isotropic superfluid through small apertures and channels. Here, a detailed comparison is made between the theory and a wide array of experimental data. First, the calculated resistance to steady superflow is compared with measurements taken in a constant pressure-head flow cell. Second, the resonant frequency and Q of three different helmholtz oscillators are compared with predictions based on the calculated frequency response. The resonant frequency and Q are extracted numerically from the frequency response, and analytical results are given in experimentally important limits. Finally, the measured and calculated frequency response are compared at a temperature where the Helmholtz oscillator differs significantly from a simple harmonic oscillator. This difference is used to explain how the thermal properties of the oscillator affect its response. The quantitative agreement between the theory and experiment provide an excellent check of the previously derived equations. Also, the limiting expressions shown in this paper provide simple analytical expressions for calculating the effects of the various physical phenomena in a particular experimental situation.https://resolver.caltech.edu/CaltechAUTHORS:20160523-151326888Detection of absolute rotation using superfluid ^4He
https://resolver.caltech.edu/CaltechAUTHORS:20111220-134626966
Year: 1998
DOI: 10.1063/1.593549
We have developed the superfluid analog of the superconducting rf SQUID. Such a device is a quantum mechanically based, absolute gyroscope and has been used to sense the rotation of the Earth. Our device is fabricated using silicon processing techniques and forms a planer sensing loop of superfluid helium which couples to the applied rotation. A much more sensitive superfluid gyroscope based on the principle's demonstrated with this device, might ultimately be used to detect the precession of our local inertial frame with respect to the fixed stars by the gravitomagnetic field of the rotating Earth. We compare the superfluid gyroscope against two other experiments aimed at detecting this general relativistic effect.https://resolver.caltech.edu/CaltechAUTHORS:20111220-134626966The Superfluid ^4He Analog of the RF SQUID
https://resolver.caltech.edu/CaltechAUTHORS:20160523-124647298
Year: 1998
DOI: 10.1023/A:1022364200234
We describe the theory, design, fabrication, and performance of a super fluid ^4He device which is the analog of the superconducting RF SQUID. This device is a sensitive rotation detector and is used to sense the rotation of the Earth. We also describe the experimental developments and observations which lead to the construction of this successful device.https://resolver.caltech.edu/CaltechAUTHORS:20160523-124647298Measurement of the quantum of thermal conductance
https://resolver.caltech.edu/CaltechAUTHORS:20150330-095451760
Year: 2000
DOI: 10.1038/35010065
The physics of mesoscopic electronic systems has been explored for more than 15 years. Mesoscopic phenomena in transport processes occur when the wavelength or the coherence length of the carriers becomes comparable to, or larger than, the sample dimensions. One striking result in this domain is the quantization of electrical conduction, observed in a quasi-one-dimensional constriction formed between reservoirs of two-dimensional electron gas. The conductance of this system is determined by the number of participating quantum states or 'channels' within the constriction; in the ideal case, each spin-degenerate channel contributes a quantized unit of 2e^2/h to the electrical conductance. It has been speculated that similar behaviour should be observable for thermal transport in mesoscopic phonon systems. But experiments attempted in this regime have so far yielded inconclusive results. Here we report the observation of a quantized limiting value for the thermal conductance, G_(th), in suspended insulating nanostructures at very low temperatures. The behaviour we observe is consistent with predictions for phonon transport in a ballistic, one-dimensional channel: at low temperatures, G_(th) approaches a maximum value of g_0 = π^2k^2BT/3h, the universal quantum of thermal conductance.https://resolver.caltech.edu/CaltechAUTHORS:20150330-095451760Quantized thermal conductance: measurements in nanostructures
https://resolver.caltech.edu/CaltechAUTHORS:20160523-075515663
Year: 2000
DOI: 10.1016/S0921-4526(99)01835-9
We are performing experiments to probe directly the thermal conductance of suspended nanostructures with lateral dimensions ≈100 nm. It has been recently predicted that at low temperatures, thermal conductance in such a structure approaches a universal value of π^2k_B^2T/3h for each massless, ballistic phonon channel, independent of material characteristics. We have developed ultra-sensitive, low dissipation DC-SQUID-based noise thermometry, and extreme isolation from the electronic environment in order to perform this measurement at temperatures below 70 mK.https://resolver.caltech.edu/CaltechAUTHORS:20160523-075515663Quantum measurement with nanomechanical systems
https://resolver.caltech.edu/CaltechAUTHORS:20160523-122135722
Year: 2001
The technology exists for preparing and measuring nanoscale mechanical systems at the quantum limit. A nanomechanical system has recently demonstrated the fundamental limit for heat flow through discrete channels. This universal energy transport limit is intimately related to the predicted maximum information rate per channel. I will discuss this measurement and experiments that are under preparation at LPS, using nanomechanical resonators with rf-SET read-out to achieve positive detection limited by the uncertainty principle: the standard quantum limit. This system offers the possibility of implementing advanced measurement strategies, such as quantum non-demolition techniques, to beat this limit. In addition to revealing the fascinating collective quantum behavior of 10^(10) atoms, developing ultra0sensitive position sensors may be important for quantum computing applications such as single electron spin read-out with cantilevers, and provide an understanding of the interaction between delicate quantum systems and real read-out devices.https://resolver.caltech.edu/CaltechAUTHORS:20160523-122135722Thermal conductance through discrete quantum channels
https://resolver.caltech.edu/CaltechAUTHORS:20160523-074636767
Year: 2001
DOI: 10.1016/S1386-9477(00)00178-8
We have observed a quantized limiting value of the thermal conductance for each propagating phonon channel in a one-dimensional (1D), ballistic phonon waveguide: g_0=π^2k_B^2T/3h. To achieve this we have developed nanostructures with full three-dimensional relief that incorporate integral thermometers and heaters. These devices are comprised of an isolated thermal reservoir (phonon cavity) suspended above the sample substrate by four narrow insulating beams (phonon waveguides) with lateral dimensions ∼100 nm. We employ DC SQUID noise thermometry to measure the temperature of the phonon cavity non-perturbatively. Direct electrical contact from the suspended nanostructure to the room-temperature environment, crucial for these experiments, is attained by means of a very significant level of electrical filtering. These first experiments provide access to the mesoscopic regime for phonons, and open intriguing future possibilities for exploring thermal transport in very small systems. We are currently adapting and improving the ultrasensitive, extremely low dissipation DC SQUID techniques utilized in this work toward the ultimate goal of detecting individual thermal phonons.https://resolver.caltech.edu/CaltechAUTHORS:20160523-074636767Spring constant and damping constant tuning of nanomechanical resonators using a single-electron transistor
https://resolver.caltech.edu/CaltechAUTHORS:20160523-072210121
Year: 2002
DOI: 10.1063/1.1449533
By fabricating a single-electron transistor onto a mechanical system in a high magnetic field, it is shown that one can manipulate both the mechanical spring constant and damping constant by adjusting a potential of a nearby gate electrode. The spring constant effect is shown to be usable to control the resonant frequency of silicon-based nanomechanical resonators, while an additional damping constant effect is relevant for the resonators built upon carbon nanotube or similar molecular-sized materials. This could prove to be a very convenient scheme to actively control the response of nanomechanical systems for a variety of applications including radio-frequency signal processing, ultrasensitive force detection, and fundamental physics explorations.https://resolver.caltech.edu/CaltechAUTHORS:20160523-072210121Entanglement and Decoherence of a Micromechanical Resonator via Coupling to a Cooper-Pair Box
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092253127
Year: 2002
DOI: 10.1103/PhysRevLett.88.148301
We analyze the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper-pair box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the decay of the resonator superposition state due to environmental decoherence.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092253127Mechanical Lamb-shift analogue for the Cooper-pair box
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252955
Year: 2002
DOI: 10.1016/S0921-4526(02)00527-6
We estimate the correction to the Cooper-pair box energy level splitting due to the quantum motion of a coupled micromechanical gate electrode. While the correction due to zero-point motion is very small, it should be possible to observe thermal motion-induced corrections to the photon-assisted tunneling current.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252955Phonon scattering mechanisms in suspended nanostructures from 4 to 40 K
https://resolver.caltech.edu/CaltechAUTHORS:FONprb02
Year: 2002
DOI: 10.1103/PhysRevB.66.045302
We have developed specially designed semiconductor devices for the measurement of thermal conductance in suspended nanostructures. By means of a novel subtractive comparison, we are able to deduce the phonon thermal conductance of individual nanoscale beams of different geometry and dopant profiles. The separate roles of important phonon scattering mechanisms are analyzed and a quantitative estimation of their respective scattering rates is obtained using the Callaway model. Diffuse surface scattering proves to be particularly important in the temperature range from 4 to 40 K. The rates of other scattering mechanisms, arising from phonon-phonon, phonon-electron, and phonon-point defect interactions, also appear to be significantly higher in nanostructures than in bulk samples.https://resolver.caltech.edu/CaltechAUTHORS:FONprb02Quantum Electro-Mechanical Systems - Recipe to make a mechanical device interfere with itself
https://resolver.caltech.edu/CaltechAUTHORS:20160523-073107049
Year: 2003
DOI: 10.1007/978-94-007-1021-4_10
A dominant theme of modern physics is to show that quantum mechanics is a valid description of the world, from atomic lengths scales and upward. This pursuit is aimed at both answering questions about the apparent boundary between the classical and quantum world, and at exploiting quantum behavior for technological purpose. As a result of the intense effort in quantum computing, nano-electronic devices have entered this realm and shown themselves to be fully quantum mechanical. Single electron devices and SQUIDs have recently exhibited quantized energy levels, Schrodinger evolution, and superposition states (Nakamura et al., 1999; Friedman et al., 2000; Vion et al., 2002).https://resolver.caltech.edu/CaltechAUTHORS:20160523-073107049Quantum measurement of a coupled nanomechanical resonator–Cooper-pair box system
https://resolver.caltech.edu/CaltechAUTHORS:20160523-090223960
Year: 2003
DOI: 10.1103/PhysRevB.68.155311
We show two effects as a result of considering the second-order correction to the spectrum of a nanomechanical resonator electrostatically coupled to a Cooper-pair box. The spectrum of the Cooper-pair box is modified in a way which depends on the Fock state of the resonator. Similarly, the frequency of the resonator becomes dependent upon the state of the Cooper-pair box. We consider whether these frequency shifts could be utilized to prepare the nanomechanical resonator in a Fock state, to perform a quantum non-demolition measurement of the resonator Fock state, and to distinguish the phase states of the Cooper-pair box.https://resolver.caltech.edu/CaltechAUTHORS:20160523-090223960Feedback cooling of a nanomechanical resonator
https://resolver.caltech.edu/CaltechAUTHORS:20160523-125641059
Year: 2003
DOI: 10.1103/PhysRevB.68.235328
Cooled, low-loss nanomechanical resonators offer the prospect of directly observing the quantum dynamics of mesoscopic systems. However, the present state of the art requires cooling down to the milliKelvin regime in order to observe quantum effects. Here we present an active feedback strategy based on continuous observation of the resonator position for the purpose of obtaining these low temperatures. In addition, we apply this to an experimentally realizable configuration, where the position monitoring is carried out by a single-electron transistor. Our estimates indicate that with current technology this technique is likely to bring the required low temperatures within reach.https://resolver.caltech.edu/CaltechAUTHORS:20160523-125641059Dissipation in nanocrystalline-diamond nanomechanical resonators
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252757
Year: 2004
DOI: 10.1063/1.1646213
We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4–274 K. Using both magnetomotive network analysis and a time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T^(0.2), with Q^(–1) ≈ 10^(–4) at low temperatures. The frequency dependence of a large dissipation feature at ~35–55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252757Cooling a nanomechanical resonator using feedback: toward quantum behavior
https://resolver.caltech.edu/CaltechAUTHORS:20160523-150508492
Year: 2004
DOI: 10.1117/12.522091
Nano-electro-mechanical devices are now rapidly approaching the point where it will be possible to observe quantum mechanical behavior. However, for such behavior to be visible it is necessary to reduce the thermal motion of these devices down to temperatures in the millikelvin range. Here we consider the use of feedback control for this purpose. We analyze an experimentally realizable situation in which the position of the resonator is continuously monitored by a Single-Electron Transistor. Because the resonator is harmonic, it is possible to use a classical description of the measurement process, and we discuss both the quantum and classical descriptions. Because of this the optimal feedback algorithm can be calculated using classical control theory. We examine the quantum state of the controlled oscillator, and the achievable effective temperature. Our estimates indicate that with current experimental technology, feedback cooling is likely to bring the required milliKelvin temperatures within reach.https://resolver.caltech.edu/CaltechAUTHORS:20160523-150508492Approaching the Quantum Limit of a Nanomechanical Resonator
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252590
Year: 2004
DOI: 10.1126/science.1094419
By coupling a single-electron transistor to a high–quality factor, 19.7-megahertz nanomechanical resonator, we demonstrate position detection approaching that set by the Heisenberg uncertainty principle limit. At millikelvin temperatures, position resolution a factor of 4.3 above the quantum limit is achieved and demonstrates the near-ideal performance of the single-electron transistor as a linear amplifier. We have observed the resonator's thermal motion at temperatures as low as 56 millikelvin, with quantum occupation factors of N_(TH) = 58. The implications of this experiment reach from the ultimate limits of force microscopy to qubit readout for quantum information devices.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252590Magnetoresistive effects in planar NiFe nanoconstrictions
https://resolver.caltech.edu/CaltechAUTHORS:20160523-073700431
Year: 2004
DOI: 10.1063/1.1682831
This study focuses on domain wall resistance in Ni_(80) Fe_(20) nanowires containing narrow constrictions down to 15 nm in width. Distinct differences in the magnetoresistance curves were found to depend on the constriction size. Wider constrictions are dominated by the overall anisotropic magnetoresistance of the structure, while constrictions narrower than ∼40 nm exhibit an additional distinct contribution from a domain wall. The effect is negative and typically varies from 1% to 5%.https://resolver.caltech.edu/CaltechAUTHORS:20160523-073700431Quantum Nondemolition Squeezing of a Nanomechanical Resonator
https://resolver.caltech.edu/CaltechAUTHORS:20160523-092421535
Year: 2005
DOI: 10.1109/TNANO.2004.840171
We show that the nanoresonator position can be squeezed significantly below the ground state level by measuring the nanoresonator with a quantum point contact or a single-electron transistor and applying a periodic voltage across the detector. The mechanism of squeezing is basically a generalization of quantum nondemolition measurement of an oscillator to the case of continuous measurement by a weakly coupled detector. The quantum feedback is necessary to prevent the "heating" due to measurement back-action. We also discuss a procedure of experimental verification of the squeezed state.https://resolver.caltech.edu/CaltechAUTHORS:20160523-092421535Light-free magnetic resonance force microscopy for studies of electron spin polarized systems
https://resolver.caltech.edu/CaltechAUTHORS:20160523-144938529
Year: 2005
DOI: 10.1016/j.jmmm.2004.09.088
Magnetic resonance force microscopy is a scanned probe technique capable of three-dimensional magnetic resonance imaging. Its excellent sensitivity opens the possibility for magnetic resonance studies of spin accumulation resulting from the injection of spin polarized currents into a para-magnetic collector. The method is based on mechanical detection of magnetic resonance which requires low noise detection of cantilever displacement; so far, this has been accomplished using optical interferometry. This is undesirable for experiments on doped silicon, where the presence of light is known to enhance spin relaxation rates. We report a non-optical displacement detection scheme based on sensitive microwave capacitive readout.https://resolver.caltech.edu/CaltechAUTHORS:20160523-144938529Squeezing of a nanomechanical resonator by quantum nondemolition measurement and feedback
https://resolver.caltech.edu/CaltechAUTHORS:20160523-110713656
Year: 2005
DOI: 10.1103/PhysRevB.71.235407
We analyze squeezing of the nanoresonator state produced by periodic measurement of position by a quantum point contact or a single-electron transistor. The mechanism of squeezing is the stroboscopic quantum nondemolition measurement generalized to the case of continuous measurement by a weakly coupled detector. The magnitude of squeezing is calculated for the harmonic and stroboscopic modulations of measurement, taking into account detector efficiency and nanoresonator quality factor. We also analyze the operation of the quantum feedback, which prevents fluctuations of the wave packet center due to measurement back-action. Verification of the squeezed state can be performed in almost the same way as its preparation; a similar procedure can also be used for the force detection with sensitivity beyond the standard quantum limit.https://resolver.caltech.edu/CaltechAUTHORS:20160523-110713656Putting mechanics into quantum mechanics
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252437
Year: 2005
DOI: 10.1063/1.2012461
Nanoelectromechanical structures are starting to approach the ultimate quantum mechanical limits for detecting and exciting motion at the nanoscale. Nonclassical states of a mechanical resonator are also on the horizon.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252437Ion trap transducers for quantum electromechanical oscillators
https://resolver.caltech.edu/CaltechAUTHORS:20170310-082830253
Year: 2005
DOI: 10.1103/PhysRevA.72.041405
An enduring challenge for contemporary physics is to experimentally observe and control quantum behavior in macroscopic systems. We show that a single trapped atomic ion could be used to probe the quantum nature of a mesoscopic mechanical oscillator precooled to 4K, and furthermore, to cool the oscillator with high efficiency to its quantum ground state. The proposed experiment could be performed using currently available technology.https://resolver.caltech.edu/CaltechAUTHORS:20170310-082830253Nanoscale, Phonon-Coupled Calorimetry with Sub-Attojoule/Kelvin Resolution
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252240
Year: 2005
DOI: 10.1021/nl051345o
We have developed an ultrasensitive nanoscale calorimeter that enables heat capacity measurements upon minute, externally affixed (phonon-coupled) samples at low temperatures. For a 5 s measurement at 2 K, we demonstrate an unprecedented resolution of ΔC ~ 0.5 aJ/K (~36 000 k_B). This sensitivity is sufficient to enable heat capacity measurements upon zeptomole-scale samples or upon adsorbates with sub-monolayer coverage across the minute cross sections of these devices. We describe the fabrication and operation of these devices and demonstrate their sensitivity by measuring an adsorbed ^4He film with optimum resolution of ~3 × 10^(-5) monolayers upon an active surface area of only ~1.2 × 10^(-9) m^2.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252240Dynamics of a two-level system strongly coupled to a high-frequency quantum oscillator
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252061
Year: 2005
DOI: 10.1103/PhysRevB.72.195410
Recent experiments on quantum behavior in microfabricated solid-state systems suggest tantalizing connections to quantum optics. Several of these experiments address the prototypical problem of cavity quantum electrodynamics: a two-level system coupled to a quantum harmonic oscillator. Such devices may allow the exploration of parameter regimes outside the near-resonance and weak-coupling assumptions of the ubiquitous rotating-wave approximation (RWA), necessitating other theoretical approaches. One such approach is an adiabatic approximation in the limit that the oscillator frequency is much larger than the characteristic frequency of the two-level system. A derivation of the approximation is presented, together with a discussion of its applicability in a system consisting of a Cooper-pair box coupled to a nanomechanical resonator. Within this approximation the time evolution of the two-level-system occupation probability is calculated using both thermal- and coherent-state initial conditions for the oscillator, focusing particularly on collapse and revival phenomena. For thermal-state initial conditions parameter regimes are found in which collapse and revival regions may be clearly distinguished, unlike the erratic evolution of the thermal-state RWA model. Coherent-state initial conditions lead to complex behavior, which exhibits sensitive dependence on the coupling strength and the initial amplitude of the oscillator state. One feature of the regime considered here is that closed-form evaluation of the time evolution may be carried out in the weak-coupling limit, which provides insight into the differences between the thermal- and coherent-state models. Finally, potential experimental observations in solid-state systems, particularly the Cooper-pair box—nanomechanical resonator system, are discussed and found to be promising.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092252061Comment on "Evidence for Quantized Displacement in Macroscopic Nanomechanical Oscillators"
https://resolver.caltech.edu/CaltechAUTHORS:SCHWprl05comm
Year: 2005
DOI: 10.1103/PhysRevLett.95.248901
In a recent Letter, Gaidarzhy et al. [1] claim to have observed evidence for "quantized displacements" of a high-order mode of a nanomechanical oscillator. We contend that the methods employed by the authors are unsuitable in principle to observe such states for any harmonic mode.https://resolver.caltech.edu/CaltechAUTHORS:SCHWprl05commIon trap in a semiconductor chip
https://resolver.caltech.edu/CaltechAUTHORS:20160523-114031722
Year: 2006
DOI: 10.1038/nphys171
The electromagnetic manipulation of isolated atoms has led to many advances in physics, from laser cooling and Bose–Einstein condensation of cold gases to the precise quantum control of individual atomic ions. Work on miniaturizing electromagnetic traps to the micrometre scale promises even higher levels of control and reliability. Compared with 'chip traps' for confining neutral atoms, ion traps with similar dimensions and power dissipation offer much higher confinement forces and allow unparalleled control at the single-atom level. Moreover, ion microtraps are of great interest in the development of miniature mass-spectrometer arrays, compact atomic clocks and, most notably, large-scale quantum information processors. Here we report the operation of a micrometre-scale ion trap, fabricated on a monolithic chip using semiconductor micro-electromechanical systems (MEMS) technology. We confine, laser cool and measure heating of a single ^(111)Cd^+ ion in an integrated radiofrequency trap etched from a doped gallium-arsenide heterostructure.https://resolver.caltech.edu/CaltechAUTHORS:20160523-114031722Cooling a nanomechanical resonator with quantum back-action
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251882
Year: 2006
DOI: 10.1038/nature05027
Quantum mechanics demands that the act of measurement must affect the measured object. When a linear amplifier is used to continuously monitor the position of an object, the Heisenberg uncertainty relationship requires that the object be driven by force impulses, called back-action. Here we measure the back-action of a superconducting single-electron transistor (SSET) on a radio-frequency nanomechanical resonator. The conductance of the SSET, which is capacitively coupled to the resonator, provides a sensitive probe of the latter's position; back-action effects manifest themselves as an effective thermal bath, the properties of which depend sensitively on SSET bias conditions. Surprisingly, when the SSET is biased near a transport resonance, we observe cooling of the nanomechanical mode from 550 mK to 300 mK—an effect that is analogous to laser cooling in atomic physics. Our measurements have implications for nanomechanical readout of quantum information devices and the limits of ultrasensitive force microscopy (such as single-nuclear-spin magnetic resonance force microscopy). Furthermore, we anticipate the use of these back-action effects to prepare ultracold and quantum states of mechanical structures, which would not be accessible with existing technology.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251882Self-cooling of a micromirror by radiation pressure
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251691
Year: 2006
DOI: 10.1038/nature05273
Cooling of mechanical resonators is currently a popular topic in many fields of physics including ultra-high precision measurements1, detection of gravitational waves, and the study of the transition between classical and quantum behaviour of a mechanical system. Here we report the observation of self-cooling of a micromirror by radiation pressure inside a high-finesse optical cavity. In essence, changes in intensity in a detuned cavity, as caused by the thermal vibration of the mirror, provide the mechanism for entropy flow from the mirror's oscillatory motion to the low-entropy cavity field. The crucial coupling between radiation and mechanical motion was made possible by producing free-standing micromirrors of low mass (m ≈ 400 ng), high reflectance (more than 99.6%) and high mechanical quality (Q ≈ 10,000). We observe cooling of the mechanical oscillator by a factor of more than 30; that is, from room temperature to below 10 K. In addition to purely photothermal effects we identify radiation pressure as a relevant mechanism responsible for the cooling. In contrast with earlier experiments, our technique does not need any active feedback. We expect that improvements of our method will permit cooling ratios beyond 1,000 and will thus possibly enable cooling all the way down to the quantum mechanical ground state of the micromirror.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251691Quantum physics: Information on heat
https://resolver.caltech.edu/CaltechAUTHORS:20160523-070945328
Year: 2006
DOI: 10.1038/444161a
In the past 20 years, physicists have learnt a tremendous amount about the transport of matter and energy through devices small enough for quantum effects to come into play. One surprising fact that has emerged is that the rates of transport in such devices, expressed for example by their electronic or thermal conductance, have simple quantum-mechanical limits. On page 187 of this issue, Meschke et al. extend this principle to heat conduction by photons. Although the result will certainly have practical ramifications for the engineering of ultra-sensitive detectors, sensors and microelectronic refrigerators, the physics behind it hints at more fundamental truths.https://resolver.caltech.edu/CaltechAUTHORS:20160523-070945328High reflectivity high-Q micromechanical Bragg mirror
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251503
Year: 2006
DOI: 10.1063/1.2393000
The authors report on the fabrication and characterization of a micromechanical oscillator consisting only of a freestanding dielectric Bragg mirror with high optical reflectivity and high mechanical quality. The fabrication technique is a hybrid approach involving laser ablation and dry etching. The mirror has a reflectivity of 99.6%, a mass of 400 ng, and a mechanical quality factor Q of approximately 10^4. Using this micromirror in a Fabry-Pérot cavity, a finesse of 500 has been achieved. This is an important step towards designing tunable high-Q high-finesse cavities on chip.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251503Efficient and Sensitive Capacitive Readout of Nanomechanical Resonator Arrays
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251330
Year: 2007
DOI: 10.1021/nl062278g
Here we describe all-electronic broadband motion detection in radio frequency nanomechanical resonators. Our technique relies upon the measurement of small motional capacitance changes using an LC impedance transformation network. We first demonstrate the technique on a single doubly clamped beam resonator with a side gate over a wide range of temperatures from 20 mK to 300 K. We then apply the technique to accomplish multiplexed readout of an array of individually addressable resonators, all embedded in a single high-frequency circuit. This technique may find use in a variety of applications ranging from ultrasensitive mass and force sensing to quantum information processing.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251330Radio-frequency scanning tunnelling microscopy
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251147
Year: 2007
DOI: 10.1038/nature06238
The scanning tunnelling microscope (STM) relies on localized electron tunnelling between a sharp probe tip and a conducting sample to attain atomic-scale spatial resolution. In the 25-year period since its invention, the STM has helped uncover a wealth of phenomena in diverse physical systems -— ranging from semiconductors to superconductors to atomic and molecular nanosystems. A severe limitation in scanning tunnelling microscopy is the low temporal resolution, originating from the diminished high-frequency response of the tunnel current readout circuitry. Here we overcome this limitation by measuring the reflection from a resonant inductor–capacitor circuit in which the tunnel junction is embedded, and demonstrate electronic bandwidths as high as 10 MHz. This ~100-fold bandwidth improvement on the state of the art translates into fast surface topography as well as delicate measurements in mesoscopic electronics and mechanics. Broadband noise measurements across the tunnel junction using this radio-frequency STM have allowed us to perform thermometry at the nanometre scale. Furthermore, we have detected high-frequency mechanical motion with a sensitivity approaching ~15 fm Hz^(-1/2). This sensitivity is on par with the highest available from nanoscale optical and electrical displacement detection techniques, and the radio-frequency STM is expected to be capable of quantum-limited position measurements.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092251147Superconducting microwave cavities as quantum nanomechanical transducers
https://resolver.caltech.edu/CaltechAUTHORS:20160606-154553202
Year: 2008
DOI: 10.1109/CLEO.2008.4551955
We show how a superconducting coplanar microwave cavity can be used as a quantum limited displacement transducer for a nanomechanical resonator by demonstrating that nanomechanical squeezing can be detected in the cavity field.https://resolver.caltech.edu/CaltechAUTHORS:20160606-154553202Coupling a nanomechanical resonator to a Cooper-pair-box qubit
https://resolver.caltech.edu/CaltechAUTHORS:20160606-154552940
Year: 2008
DOI: 10.1109/CLEO.2008.4551956
We demonstrate dispersive coupling between a Cooper-pair box (CPB) qubit and a VHF NEMS (nanoelectromechanical systems) resonator. The observed interaction strength is sufficient to pursue more advanced experiments to elicit quantum behavior in NEMS.https://resolver.caltech.edu/CaltechAUTHORS:20160606-154552940Nanomechanical squeezing with detection via a microwave cavity
https://resolver.caltech.edu/CaltechAUTHORS:20090911-092250976
Year: 2008
DOI: 10.1103/PhysRevA.78.062303
We study a parametrically driven nanomechanical resonator capacitively coupled to a microwave cavity. If the nanoresonator can be cooled to near its quantum ground state then quantum squeezing of a quadrature of the nanoresonator motion becomes feasible. We consider the adiabatic limit in which the cavity mode is slaved to the nanoresonator mode. By driving the cavity on its red-detuned sideband, the squeezing can be coupled into the microwave field at the cavity resonance. The red-detuned sideband drive is also compatible with the goal of ground state cooling. Squeezing of the output microwave field may be inferred using a technique similar to that used to infer squeezing of the field produced by a Josephson parametric amplifier, and subsequently, squeezing of the nanoresonator motion may be inferred. We have calculated the output field microwave squeezing spectra and related this to squeezing of the nanoresonator motion, both at zero and finite temperature. Driving the cavity on the blue-detuned sideband, and on both the blue and red sidebands, have also been considered within the same formalism.https://resolver.caltech.edu/CaltechAUTHORS:20090911-092250976Nanomechanical measurements of a superconducting qubit
https://resolver.caltech.edu/CaltechAUTHORS:20090827-161710676
Year: 2009
DOI: 10.1038/nature08093
The observation of the quantum states of motion of a macroscopic mechanical structure remains an open challenge in quantum-state preparation and measurement. One approach that has received extensive theoretical attention is the integration of superconducting qubits as control and detection elements in nanoelectromechanical systems (NEMS). Here we report measurements of a NEMS resonator coupled to a superconducting qubit, a Cooper-pair box. We demonstrate that the coupling results in a dispersive shift of the nanomechanical frequency that is the mechanical analogue of the 'single-atom index effect' experienced by electromagnetic resonators in cavity quantum electrodynamics. The large magnitude of the dispersive interaction allows us to perform NEMS-based spectroscopy of the superconducting qubit, and enables observation of Landau–Zener interference effects—a demonstration of nanomechanical read-out of quantum interference.https://resolver.caltech.edu/CaltechAUTHORS:20090827-161710676Demonstration of an ultracold micro-optomechanical oscillator in a cryogenic cavity
https://resolver.caltech.edu/CaltechAUTHORS:20090828-161056938
Year: 2009
DOI: 10.1038/nphys1301
Preparing and manipulating quantum states of mechanical resonators is a highly interdisciplinary undertaking that now receives enormous interest for its far-reaching potential in fundamental and applied science. Up to now, only nanoscale mechanical devices achieved operation close to the quantum regime. We report a new micro-optomechanical resonator that is laser cooled to a level of 30 thermal quanta. This is equivalent to the best nanomechanical devices, however, with a mass more than four orders of magnitude larger (43 ng versus 1 pg) and at more than two orders of magnitude higher environment temperature (5 K versus 30 mK). Despite the large laser-added cooling factor of 4,000 and the cryogenic environment, our cooling performance is not limited by residual absorption effects. These results pave the way for the preparation of 100-m scale objects in the quantum regime. Possible applications range from quantum-limited optomechanical sensing devices to macroscopic tests of quantum physics.https://resolver.caltech.edu/CaltechAUTHORS:20090828-161056938Preparation and detection of a mechanical resonator near the ground state of motion
https://resolver.caltech.edu/CaltechAUTHORS:20100128-133901103
Year: 2010
DOI: 10.1038/nature08681
Cold, macroscopic mechanical systems are expected to behave contrary to our usual classical understanding of reality; the most striking and counterintuitive predictions involve the existence of states in which the mechanical system is located in two places simultaneously. Various schemes have been proposed to generate and detect such states, and all require starting from mechanical states that are close to the lowest energy eigenstate, the mechanical ground state. Here we report the cooling of the motion of a radio-frequency nanomechanical resonator by parametric coupling to a driven, microwave-frequency superconducting resonator. Starting from a thermal occupation of 480 quanta, we have observed occupation factors as low as 3.8 ± 1.3 and expect the mechanical resonator to be found with probability 0.21 in the quantum ground state of motion. Further cooling is limited by random excitation of the microwave resonator and heating of the dissipative mechanical bath. This level of cooling is expected to make possible a series of fundamental quantum mechanical observations including direct measurement of the Heisenberg uncertainty principle and quantum entanglement with qubits.https://resolver.caltech.edu/CaltechAUTHORS:20100128-133901103Back-action-evading measurements of nanomechanical motion
https://resolver.caltech.edu/CaltechAUTHORS:20100408-094321850
Year: 2010
DOI: 10.1038/nphys1479
When carrying out ultrasensitive continuous measurements of position, one must ultimately confront the fundamental effects of detection back-action. Back-action forces set a lower bound on the uncertainty in the measured position, the 'standard quantum limit' (SQL). Recent measurements of nano- and micromechanical resonators are rapidly approaching this limit. Making measurements with sensitivities surpassing the SQL will require a new kind of approach: back-action-evading (BAE), quantum non-demolition measurement techniques. Here we realize a BAE measurement based on the parametric coupling between a nanomechanical and a microwave resonator. We demonstrate for the first time BAE detection of a single quadrature of motion with sensitivity four times the quantum zero-point motion of the mechanical resonator. We identify a limiting parametric instability inherent in BAE measurement, and describe how to improve the technique to surpass the SQL and permit the formation of squeezed states of motion.https://resolver.caltech.edu/CaltechAUTHORS:20100408-094321850Parametric Amplification and Back-Action Noise Squeezing by a Qubit-Coupled Nanoresonator
https://resolver.caltech.edu/CaltechAUTHORS:20101102-084452139
Year: 2010
DOI: 10.1021/nl101844r
We demonstrate the parametric amplification and noise squeezing of nanomechanical motion utilizing dispersive coupling
to a Cooper-pair box qubit. By modulating the qubit bias and resulting mechanical resonance shift, we achieve gain of 30 dB and
noise squeezing of 4 dB. This qubit-mediated effect is 3000 times more effective than that resulting from the weak nonlinearity of
capacitance to a nearby electrode. This technique may be used to prepare nanomechanical squeezed states.https://resolver.caltech.edu/CaltechAUTHORS:20101102-084452139Quantum-measurement backaction from a Bose-Einstein condensate coupled to a mechanical oscillator
https://resolver.caltech.edu/CaltechAUTHORS:20110912-085804452
Year: 2011
DOI: 10.1103/PhysRevA.84.023841
We study theoretically the dynamics of a hybrid optomechanical system consisting of a macroscopic mechanical membrane magnetically coupled to a spinor Bose-Einstein condensate via a nanomagnet attached at the membrane center. We demonstrate that this coupling permits us to monitor indirectly the center-of-mass position of the membrane via measurements of the spin of the condensed atoms. These measurements normally induce a significant backaction on the membrane motion, which we quantify for the cases of thermal and coherent initial states of the membrane. We discuss the possibility of measuring this quantum backaction via repeated measurements. We also investigate the potential to generate nonclassical states of the membrane, in particular Schrödinger-cat states, via such repeated measurements.https://resolver.caltech.edu/CaltechAUTHORS:20110912-085804452Quantum optomechanics
https://resolver.caltech.edu/CaltechAUTHORS:20120711-111331625
Year: 2012
DOI: 10.1063/PT.3.1640
Aided by optical cavities and superconducting circuits, researchers are coaxing ever-larger objects to wiggle, shake, and flex in ways that are distinctly quantum mechanical.https://resolver.caltech.edu/CaltechAUTHORS:20120711-111331625Ultrasensitive and Wide-Bandwidth Thermal Measurements of Graphene at Low Temperatures
https://resolver.caltech.edu/CaltechAUTHORS:20120313-081134132
Year: 2012
DOI: 10.1103/PhysRevX.2.031006
Graphene is a material with remarkable electronic properties[1] and exceptional thermal transport
properties near room temperature, which have been well examined and understood[2, 3].
However at very low temperatures the thermodynamic and thermal transport properties are much
less well explored[4, 5] and somewhat surprisingly, is expected to exhibit extreme thermal isolation.
Here we demonstrate an ultra-sensitive, wide-bandwidth measurement scheme to probe the
thermal transport and thermodynamic properties of the electron gas of graphene. We employ
Johnson noise thermometry at microwave frequency to sensitively measure the temperature of the
electron gas with resolution of 4mK/√Hz and a bandwidth of 80 MHz. We have measured the
electron-phonon coupling from 2-30 K at a charge density of 2 •10^(11)cm^(-2). Utilizing bolometric
mixing, we have sensed temperature oscillations with period of 430 ps and have determined the
heat capacity of the electron gas to be 2 • 10^(-21)J/(K •µm^2) at 5 K which is consistent with that
of a two dimensional, Dirac electron gas. These measurements suggest that graphene-based devices
together with wide bandwidth noise thermometry can generate substantial advances in the
areas of ultra-sensitive bolometry[6], calorimetry[7], microwave and terahertz photo-detection[8],
and bolometric mixing for applications in areas such as observational astronomy[9] and quantum
information and measurement[10].https://resolver.caltech.edu/CaltechAUTHORS:20120313-081134132Macroscopic quantum resonators (MAQRO) - Testing quantum and gravitational physics with massive mechanical resonators
https://resolver.caltech.edu/CaltechAUTHORS:20121102-150900422
Year: 2012
DOI: 10.1007/s10686-012-9292-3
Quantum physics challenges our understanding of the nature of physical reality and of space-time and suggests the necessity of radical revisions of their underlying concepts. Experimental tests of quantum phenomena involving massive macroscopic objects would provide novel insights into these fundamental questions. Making use of the unique environment provided by space, MAQRO aims at investigating this largely unexplored realm of macroscopic quantum physics. MAQRO has originally been proposed as a medium-sized fundamental-science space mission for the 2010 call of Cosmic Vision. MAQRO unites two experiments: DECIDE (DECoherence In Double-Slit Experiments) and CASE (Comparative Acceleration Sensing Experiment). The main scientific objective of MAQRO, which is addressed by the experiment DECIDE, is to test the predictions of quantum theory for quantum superpositions of macroscopic objects containing more than 108 atoms. Under these conditions, deviations due to various suggested alternative models to quantum theory would become visible. These models have been suggested to harmonize the paradoxical quantum phenomena both with the classical macroscopic world and with our notion of Minkowski space-time. The second scientific objective of MAQRO, which is addressed by the experiment CASE, is to demonstrate the performance of a novel type of inertial sensor based on optically trapped microspheres. CASE is a technology demonstrator that shows how the modular design of DECIDE allows to easily incorporate it with other missions that have compatible requirements in terms of spacecraft and orbit. CASE can, at the same time, serve as a test bench for the weak equivalence principle, i.e., the universality of free fall with test-masses differing in their mass by 7 orders of magnitude.https://resolver.caltech.edu/CaltechAUTHORS:20121102-150900422Thermally Induced Parametric Instability in a Back-Action Evading Measurement of a Micromechanical Quadrature near the Zero-Point Level
https://resolver.caltech.edu/CaltechAUTHORS:20130108-140901859
Year: 2012
DOI: 10.1021/nl303353r
We report the results of back-action evading experiments
utilizing a tightly coupled electro-mechanical system formed by a radio
frequency micromechanical resonator parametrically coupled to a NbTiN
superconducting microwave resonator. Due to excess dissipation in the
microwave resonator, we observe a parametric instability induced by a thermal
shift of the mechanical resonance frequency. In light of these measurements,
we discuss the constraints on microwave dissipation needed to perform BAE
measurements far below the zero-point level.https://resolver.caltech.edu/CaltechAUTHORS:20130108-140901859Optomechanical effects of two-level systems in a back-action evading measurement of micro-mechanical motion
https://resolver.caltech.edu/CaltechAUTHORS:20130930-142615270
Year: 2013
DOI: 10.1063/1.4816428
We show that the two-level systems (TLS) in lithographic superconducting circuits act as a power-dependent dielectric leading to non-linear responses in a parametrically coupled electromechanical system. Driven TLS shift the microwave resonance frequency and modulate the mechanical resonance through the optical spring effect. By pumping with two tones in a back-action evading measurement, these effects produce a mechanical parametric instability which limits single quadrature imprecision to 1.4 x_(zp). The microwave resonator noise is also consistent to a TLS-noise model. These observations suggest design strategies for minimizing TLS effects to improve ground-state cooling and quantum non-demolition measurements of motion.https://resolver.caltech.edu/CaltechAUTHORS:20130930-142615270Optomechanical backaction-evading measurement without parametric instability
https://resolver.caltech.edu/CaltechAUTHORS:20130917-103836848
Year: 2013
DOI: 10.1103/PhysRevA.88.023838
We review a scheme for performing a backaction-evading measurement of one mechanical quadrature in an optomechanical setup. The experimental application of this scheme has been limited by parametric instabilities caused in general by a slight dependence of the mechanical frequency on the electromagnetic energy in the cavity. We find that a simple modification to the optical drive can effectively eliminate the parametric instability even at high intracavity power, allowing realistic devices to achieve sub-zero-point uncertainties in the measured quadrature.https://resolver.caltech.edu/CaltechAUTHORS:20130917-103836848Linear and nonlinear coupling between transverse modes of a nanomechanical resonator
https://resolver.caltech.edu/CaltechAUTHORS:20131024-082601069
Year: 2013
DOI: 10.1063/1.4821273
We measure both the linear and nonlinear coupling between transverse modes in a nanomechanical resonator. The nonlinear coupling is due to the displacement dependent tension of the resonator and leads to a frequency shift ("pulling") of each mode proportional to the square of the orthogonal mode's displacement amplitude. The linear coupling is apparent as an avoided crossing of the resonant frequencies that occurs when one electrostatically tunes the modes into degeneracy via a nearby DC gate. We consider the possibility that the linear coupling results from an electrostatic interaction and find that this effect can only partially explain the magnitude of the observed coupling. By measuring the coupled amplitudes magnetomotively at various angles to the applied field, we find that as the modes are tuned through the degeneracy point, they remain linearly polarized, while their planes of vibration rotate by 90°.https://resolver.caltech.edu/CaltechAUTHORS:20131024-082601069Measurement of the Electronic Thermal Conductance Channels and Heat Capacity of Graphene at Low Temperature
https://resolver.caltech.edu/CaltechAUTHORS:20130827-110003002
Year: 2013
DOI: 10.1103/PhysRevX.3.041008
The ability to transport energy is a fundamental property of the two-dimensional Dirac fermions in graphene. Electronic thermal transport in this system is relatively unexplored and is expected to show unique fundamental properties and to play an important role in future applications of graphene, including optoelectronics, plasmonics, and ultrasensitive bolometry. Here, we present measurements of bipolar thermal conductances due to electron diffusion and electron-phonon coupling and infer the electronic specific heat, with a minimum value of 10k_B (10^(−22) J/K) per square micron. We test the validity of the Wiedemann-Franz law and find that the Lorenz number equals 1.32×(π^2/3)(kB/^e)^2. The electron-phonon thermal conductance has a temperature power law T^2 at high doping levels, and the coupling parameter is consistent with recent theory, indicating its enhancement by impurity scattering. We demonstrate control of the thermal conductance by electrical gating and by suppressing the diffusion channel using NbTiN superconducting electrodes, which sets the stage for future graphene-based single-microwave photon detection.https://resolver.caltech.edu/CaltechAUTHORS:20130827-110003002Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate
https://resolver.caltech.edu/CaltechAUTHORS:20140515-161526294
Year: 2013
DOI: 10.1088/1367-2630/16/11/113020
We investigate the low loss acoustic motion of superfluid ^4He parametrically coupled to a very low loss, superconducting Nb, TE_(011) microwave resonator, forming a gram-scale, sideband resolved, optomechanical system. We demonstrate the detection of a series of acoustic modes with quality factors as high as 7⋅10^6. At higher temperatures, the lowest dissipation modes are limited by an intrinsic three phonon process. Acoustic quality factors approaching 10^(11) may be possible in isotopically purified samples at temperatures below 10 mK. A system of this type may be utilized to study macroscopic quantized motion and as an ultra-sensitive sensor of extremely weak displacements and forces, such as continuous gravity wave sources.https://resolver.caltech.edu/CaltechAUTHORS:20140515-161526294Quantum backaction in spinor-condensate magnetometry
https://resolver.caltech.edu/CaltechAUTHORS:20140116-151510121
Year: 2013
DOI: 10.1103/PhysRevA.88.063809
We provide a theoretical treatment of the quantum backaction of Larmor frequency measurements on a spinor Bose-Einstein condensate by an off-resonant light field. Two main results are presented; the first is a "quantum jump" operator description that reflects the abrupt change in the spin state of the atoms when a single photon is counted at a photodiode. The second is the derivation of a conditional stochastic master equation relating the evolution of the condensate density matrix to the measurement record. We provide a few examples of the application of this formalism and comment on its application to metrology.https://resolver.caltech.edu/CaltechAUTHORS:20140116-151510121Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field
https://resolver.caltech.edu/CaltechAUTHORS:20140515-115038262
Year: 2014
DOI: 10.1126/science.1253258
Quantum fluctuations of the light field used for continuous position detection produces stochastic back-action forces and ultimately limits the sensitivity. To overcome this limit, the back-action forces can be avoided by giving up complete knowledge of the motion, and these types of measurements are called "back-action evading" or "quantum nondemolition" detection. We present continuous two-tone back-action evading measurements with a superconducting electromechanical device, realizing three long-standing goals: detection of back-action forces due to the quantum noise of a microwave field, reduction of this quantum back-action noise by 8.5 ± 0.4 dB, and measurement imprecision of a single quadrature of motion 2.4 ± 0.7 dB below the mechanical zero-point fluctuations. Measurements of this type will find utility in ultrasensitive measurements of weak forces and nonclassical states of motion.https://resolver.caltech.edu/CaltechAUTHORS:20140515-115038262Observation and interpretation of motional sideband asymmetry in a quantum electro-mechanical device
https://resolver.caltech.edu/CaltechAUTHORS:20140515-160500332
Year: 2014
DOI: 10.1103/PhysRevX.4.041003
Quantum electromechanical systems offer a unique opportunity to probe quantum noise properties in macroscopic devices, properties that ultimately stem from Heisenberg's uncertainty relations. A simple example of this behavior is expected to occur in a microwave parametric transducer, where mechanical motion generates motional sidebands corresponding to the up-and-down frequency conversion of microwave photons. Because of quantum vacuum noise, the rates of these processes are expected to be unequal. We measure this fundamental imbalance in a microwave transducer coupled to a radio-frequency mechanical mode, cooled near the ground state of motion. We also discuss the subtle origin of this imbalance: depending on the measurement scheme, the imbalance is most naturally attributed to the quantum fluctuations of either the mechanical mode or of the electromagnetic field.https://resolver.caltech.edu/CaltechAUTHORS:20140515-160500332Quantum squeezing of motion in a mechanical resonator
https://resolver.caltech.edu/CaltechAUTHORS:20150728-095253969
Year: 2015
DOI: 10.1126/science.aac5138
According to quantum mechanics, a harmonic oscillator can never be completely at rest. Even in the ground state, its position will always have fluctuations, called the zero-point motion. Although the zero-point fluctuations are unavoidable, they can be manipulated. Using microwave frequency radiation pressure, we have manipulated the thermal fluctuations of a micrometer-scale mechanical resonator to produce a stationary quadrature-squeezed state with a minimum variance of 0.80 times that of the ground state. We also performed phase-sensitive, back-action evading measurements of a thermal state squeezed to 1.09 times the zero-point level. Our results are relevant to the quantum engineering of states of matter at large length scales, the study of decoherence of large quantum systems, and for the realization of ultrasensitive sensing of force and motion.https://resolver.caltech.edu/CaltechAUTHORS:20150728-095253969Mesoscopic mechanical resonators as quantum noninertial reference frames
https://resolver.caltech.edu/CaltechAUTHORS:20151019-143210259
Year: 2015
DOI: 10.1103/PhysRevA.92.042104
An atom attached to a micrometer-scale wire that is vibrating at a frequency ∼100 MHz and with displacement amplitude ∼1 nm experiences an acceleration magnitude ∼10^9 m s^(−2), approaching the surface gravity of a neutron star. As one application of such extreme noninertial forces in a mesoscopic setting, we consider a model two-path atom interferometer with one path consisting of the 100 MHz vibrating wire atom guide. The vibrating wire guide serves as a noninertial reference frame and induces an in principle measurable phase shift in the wave function of an atom traversing the wire frame. We furthermore consider the effect on the two-path atom wave
interference when the vibrating wire is modeled as a quantum object, hence functioning as a quantum noninertial reference frame. We outline a possible realization of the vibrating wire, atom interferometer using a superfluid helium quantum interference setup.https://resolver.caltech.edu/CaltechAUTHORS:20151019-143210259Macroscopic quantum resonators (MAQRO): 2015 Update
https://resolver.caltech.edu/CaltechAUTHORS:20160523-080435297
Year: 2015
DOI: 10.1140/epjqt/s40507-016-0043-7
Do the laws of quantum physics still hold for macroscopic objects - this is at the heart of Schrödinger's cat paradox - or do gravitation or yet unknown effects set a limit for massive particles? What is the fundamental relation between quantum physics and gravity? Ground-based experiments addressing these questions may soon face limitations due to limited free-fall times and the quality of vacuum and microgravity. The proposed mission Macroscopic Quantum Resonators (MAQRO) may overcome these limitations and allow addressing such fundamental questions. MAQRO harnesses recent developments in quantum optomechanics, high-mass matter-wave interferometry as well as state-of-the-art space technology to push macroscopic quantum experiments towards their ultimate performance limits and to open new horizons for applying quantum technology in space. The main scientific goal is to probe the vastly unexplored 'quantum-classical' transition for increasingly massive objects, testing the predictions of quantum theory for objects in a size and mass regime unachievable in ground-based experiments. The hardware will largely be based on available space technology. Here, we present the MAQRO proposal submitted in response to the 4th Cosmic Vision call for a medium-sized mission (M4) in 2014 of the European Space Agency (ESA) with a possible launch in 2025, and we review the progress with respect to the original MAQRO proposal for the 3rd Cosmic Vision call for a medium-sized mission (M3) in 2010. In particular, the updated proposal overcomes several critical issues of the original proposal by relying on established experimental techniques from high-mass matter-wave interferometry and by introducing novel ideas for particle loading and manipulation. Moreover, the mission design was improved to better fulfill the stringent environmental requirements for macroscopic quantum experiments.https://resolver.caltech.edu/CaltechAUTHORS:20160523-080435297Nonlinear Quantum Dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20160523-093923704
Year: 2016
DOI: 10.48550/arXiv.0505046
The vast majority of the literature dealing with quantum dynamics is concerned with linear evolution of the wave function or the density matrix. A complete dynamical description requires a full understanding of the evolution of measured quantum systems, necessary to explain actual experimental results. The dynamics of such systems is intrinsically nonlinear even at the level of distribution functions, both classically as well as quantum mechanically. Aside from being physically more complete, this treatment reveals the existence of dynamical regimes, such as chaos, that have no counterpart in the linear case. Here, we present a short introductory review of some of these aspects, with a few illustrative results and examples.https://resolver.caltech.edu/CaltechAUTHORS:20160523-093923704Quantum Nondemolition Measurement of a Quantum Squeezed State Beyond the 3 dB Limit
https://resolver.caltech.edu/CaltechAUTHORS:20160831-100027142
Year: 2016
DOI: 10.1103/PhysRevLett.117.100801
We use a reservoir engineering technique based on two-tone driving to generate and stabilize a quantum squeezed state of a micron-scale mechanical oscillator in a microwave optomechanical system. Using an independent backaction-evading measurement to directly quantify the squeezing, we observe 4.7±0.9 dB of squeezing below the zero-point level surpassing the 3 dB limit of standard parametric squeezing techniques. Our measurements also reveal evidence for an additional mechanical parametric effect. The interplay between this effect and the optomechanical interaction enhances the amount of squeezing obtained in the experiment.https://resolver.caltech.edu/CaltechAUTHORS:20160831-100027142Ultra-High Q Acoustic Resonance in Superfluid ^4He
https://resolver.caltech.edu/CaltechAUTHORS:20161109-083656556
Year: 2017
DOI: 10.1007/s10909-016-1674-x
We report the measurement of the acoustic quality factor of a gram-scale, kilohertz-frequency superfluid resonator, detected through the parametric coupling to a superconducting niobium microwave cavity. For temperatures between 400 mK and 50 mK, we observe a T^(−4) temperature dependence of the quality factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors up to 1.4×10^8, consistent with the dissipation due to dilute ^3He impurities, and expect that significant further improvements are possible. These experiments are relevant to exploring quantum behavior and decoherence of massive macroscopic objects, the laboratory detection of continuous gravitational waves from pulsars, and the probing of possible limits to physical length scales.https://resolver.caltech.edu/CaltechAUTHORS:20161109-083656556Detecting continuous gravitational waves with superfluid ^4He
https://resolver.caltech.edu/CaltechAUTHORS:20170313-065536926
Year: 2017
DOI: 10.1088/1367-2630/aa78cb
Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high Q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1–1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For thermal noise limited sensitivity, we find that strain fields on the order of h ~ 10^(-23)/√Hz are detectable. Measuring such strains is possible by implementing state of the art microwave transducer technology. We show that the proposed system can compete with interferometric detectors and potentially surpass the gravitational strain limits set by them for certain pulsar sources within a few months of integration time.https://resolver.caltech.edu/CaltechAUTHORS:20170313-065536926Resonant Thermoelectric Nanophotonics
https://resolver.caltech.edu/CaltechAUTHORS:20161004-090725146
Year: 2017
DOI: 10.1038/NNANO.2017.87
Photodetectors are typically based either on photocurrent generation from electron–hole pairs in semiconductor structures or on bolometry for wavelengths that are below bandgap absorption. In both cases, resonant plasmonic and nanophotonic structures have been successfully used to enhance performance. Here, we show subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large localized temperature gradients even with unfocused, spatially uniform illumination to generate a thermoelectric voltage. We show that such structures are tunable and are capable of wavelength-specific detection, with an input power responsivity of up to 38 V W^(–1), referenced to incident illumination, and bandwidth of nearly 3 kHz. This is obtained by combining resonant absorption and thermoelectric junctions within a single suspended membrane nanostructure, yielding a bandgap-independent photodetection mechanism. We report results for both bismuth telluride/antimony telluride and chromel/alumel structures as examples of a potentially broader class of resonant nanophotonic thermoelectric materials for optoelectronic applications such as non-bandgap-limited hyperspectral and broadband photodetectors.https://resolver.caltech.edu/CaltechAUTHORS:20161004-090725146Quantum Communication, Sensing and Measurement in Space
https://resolver.caltech.edu/CaltechAUTHORS:20190213-143112948
Year: 2019
DOI: 10.26206/PTRZ-DA93
The main theme of the conclusions drawn for classical communication systems
operating at optical or higher frequencies is that there is a well‐understood
performance gain in photon efficiency (bits/photon) and spectral efficiency
(bits/s/Hz) by pursuing coherent‐state transmitters (classical ideal laser light)
coupled with novel quantum receiver systems operating near the Holevo limit (e.g.,
joint detection receivers). However, recent research indicates that these receivers
will require nonlinear and nonclassical optical processes and components at the
receiver. Consequently, the implementation complexity of Holevo‐capacityapproaching
receivers is not yet fully ascertained. Nonetheless, because the
potential gain is significant (e.g., the projected photon efficiency and data rate of
MIT Lincoln Laboratory's Lunar Lasercom Demonstration (LLCD) could be achieved
with a factor‐of‐20 reduction in the modulation bandwidth requirement), focused
research activities on ground‐receiver architectures that approach the Holevo limit
in space‐communication links would be beneficial.
The potential gains resulting from quantum‐enhanced sensing systems in space
applications have not been laid out as concretely as some of the other areas
addressed in our study. In particular, while the study period has produced several
interesting high‐risk and high‐payoff avenues of research, more detailed seedlinglevel
investigations are required to fully delineate the potential return relative to
the state‐of‐the‐art. Two prominent examples are (1) improvements to pointing,
acquisition and tracking systems (e.g., for optical communication systems) by way
of quantum measurements, and (2) possible weak‐valued measurement techniques
to attain high‐accuracy sensing systems for in situ or remote‐sensing instruments.
While these concepts are technically sound and have very promising bench‐top
demonstrations in a lab environment, they are not mature enough to realistically
evaluate their performance in a space‐based application. Therefore, it is
recommended that future work follow small focused efforts towards incorporating
practical constraints imposed by a space environment.
The space platform has been well recognized as a nearly ideal environment for some
of the most precise tests of fundamental physics, and the ensuing potential of
scientific advances enabled by quantum technologies is evident in our report. For
example, an exciting concept that has emerged for gravity‐wave detection is that the
intermediate frequency band spanning 0.01 to 10 Hz—which is inaccessible from
the ground—could be accessed at unprecedented sensitivity with a space‐based
interferometer that uses shorter arms relative to state‐of‐the‐art to keep the
diffraction losses low, and employs frequency‐dependent squeezed light to surpass
the standard quantum limit sensitivity. This offers the potential to open up a new
window into the universe, revealing the behavior of compact astrophysical objects
and pulsars. As another set of examples, research accomplishments in the atomic
and optics fields in recent years have ushered in a number of novel clocks and
sensors that can achieve unprecedented measurement precisions. These emerging
technologies promise new possibilities in fundamental physics, examples of which
are tests of relativistic gravity theory, universality of free fall, frame‐dragging
precession, the gravitational inverse‐square law at micron scale, and new ways of gravitational wave detection with atomic inertial sensors. While the relevant
technologies and their discovery potentials have been well demonstrated on the
ground, there exists a large gap to space‐based systems. To bridge this gap and to
advance fundamental‐physics exploration in space, focused investments that further
mature promising technologies, such as space‐based atomic clocks and quantum
sensors based on atom‐wave interferometers, are recommended.
Bringing a group of experts from diverse technical backgrounds together in a
productive interactive environment spurred some unanticipated innovative
concepts. One promising concept is the possibility of utilizing a space‐based
interferometer as a frequency reference for terrestrial precision measurements.
Space‐based gravitational wave detectors depend on extraordinarily low noise in
the separation between spacecraft, resulting in an ultra‐stable frequency reference
that is several orders of magnitude better than the state of the art of frequency
references using terrestrial technology. The next steps in developing this promising
new concept are simulations and measurement of atmospheric effects that may limit
performance due to non‐reciprocal phase fluctuations.
In summary, this report covers a broad spectrum of possible new opportunities in
space science, as well as enhancements in the performance of communication and
sensing technologies, based on observing, manipulating and exploiting the
quantum‐mechanical nature of our universe. In our study we identified a range of
exciting new opportunities to capture the revolutionary capabilities resulting from
quantum enhancements. We believe that pursuing these opportunities has the
potential to positively impact the NASA mission in both the near term and in the
long term. In this report we lay out the research and development paths that we
believe are necessary to realize these opportunities and capitalize on the gains
quantum technologies can offer.https://resolver.caltech.edu/CaltechAUTHORS:20190213-143112948Toward Microwave-to-Optical Conversion using Erbium Doped Crystals and Integrated Resonators
https://resolver.caltech.edu/CaltechAUTHORS:20190712-093247697
Year: 2019
DOI: 10.1364/cleo_qels.2019.fm1a.7
We present progress towards a bidirectional coherent microwave-to-optical photon converter using an ensemble of rare-earth ions coupled to integrated photonic and microwave resonators.https://resolver.caltech.edu/CaltechAUTHORS:20190712-093247697Microwave-to-optical transduction with erbium ions coupled to planar photonic and superconducting resonators
https://resolver.caltech.edu/CaltechAUTHORS:20230613-731307200.39
Year: 2023
DOI: 10.1038/s41467-023-36799-0
PMCID: PMC9977906
Optical quantum networks can connect distant quantum processors to enable secure quantum communication and distributed quantum computing. Superconducting qubits are a leading technology for quantum information processing but cannot couple to long-distance optical networks without an efficient, coherent, and low noise interface between microwave and optical photons. Here, we demonstrate a microwave-to-optical transducer using an ensemble of erbium ions that is simultaneously coupled to a superconducting microwave resonator and a nanophotonic optical resonator. The coherent atomic transitions of the ions mediate the frequency conversion from microwave photons to optical photons and using photon counting we observed device conversion efficiency approaching 10⁻⁷. With pulsed operation at a low duty cycle, the device maintained a spin temperature below 100 mK and microwave resonator heating of less than 0.15 quanta.https://resolver.caltech.edu/CaltechAUTHORS:20230613-731307200.39Hot Carrier Thermalization and Josephson Inductance Thermometry in a Graphene-Based Microwave Circuit
https://resolver.caltech.edu/CaltechAUTHORS:20230530-441768000.65
Year: 2023
DOI: 10.1021/acs.nanolett.2c04791
Due to its exceptional electronic and thermal properties, graphene is a key material for bolometry, calorimetry, and photon detection. However, despite graphene's relatively simple electronic structure, the physical processes responsible for the heat transport from the electrons to the lattice are experimentally still elusive. Here, we measure the thermal response of low-disorder graphene encapsulated in hexagonal boron nitride by integrating it within a multiterminal superconducting microwave resonator. The device geometry allows us to simultaneously apply Joule heat power to the graphene flake while performing calibrated readout of the electron temperature. We probe the thermalization rates of both electrons and holes with high precision and observe a thermalization scaling exponent not consistent with cooling through the graphene bulk and argue that instead it can be attributed to processes at the graphene – aluminum interface. Our technique provides new insights into the thermalization pathways essential for the next-generation graphene thermal detectors.https://resolver.caltech.edu/CaltechAUTHORS:20230530-441768000.65