CaltechAUTHORS: Article
https://feeds.library.caltech.edu/people/Mabuchi-H/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 13 Sep 2024 19:12:00 -0700Test of octupole coupled 5- state in 146Nd using proton inelastic scattering
https://resolver.caltech.edu/CaltechAUTHORS:COTprc91
Year: 1991
DOI: 10.1103/PhysRevC.44.1668
The inelastic scattering of 35 MeV protons has been used to excite seven states below 2.1 MeV in 146Nd. A comparison between a coupled-channels calculation that assumes an octupole coupled structure for the 5- state at 1.517 MeV and the observed cross section suggests that the wave function of this state includes only a small two-quasiparticle component. In addition, the present results indicate that the level at 2.073 MeV, previously assigned Jπ=4-, actually has Jπ=3-.https://resolver.caltech.edu/CaltechAUTHORS:COTprc91Highly polarized muonic He produced by collisions with laser optically pumped Rb
https://resolver.caltech.edu/CaltechAUTHORS:BARprl93
Year: 1993
DOI: 10.1103/PhysRevLett.70.758
We have formed highly polarized muonic helium by stopping unpolarized negative muons in a mixture of unpolarized gaseous He and laser polarized Rb vapor. The stopped muons form muonic He ions which are neutralized and polarized by collisions with Rb. Average polarizations for 3He and 4He of (26.8±2.3)% and (44.2±3.5)% were achieved, representing a tenfold increase over previous methods. Relevant cross sections were determined from the time evolution of the polarization. Highly polarized muonic He is valuable for measurements of the induced pseudoscalar coupling gp in nuclear muon capture.https://resolver.caltech.edu/CaltechAUTHORS:BARprl93Polarization-dependent frequency shifts from Rb-3He collisions
https://resolver.caltech.edu/CaltechAUTHORS:NEWpra93
Year: 1993
DOI: 10.1103/PhysRevA.48.558
We present measurements of the frequency shift of the Rb electron-paramagnetic-resonance (EPR) line in the presence of nuclear-polarized 3He gas for the temperature range of 30 to 85 °C. The frequency shift is due to the Fermi-contact interaction between the Rb valence electron and the polarized 3He nucleus. Expressions for both the frequency shift and the spin-exchange cross section are derived in terms of the strength of this contact interaction. From these expressions and the measured frequency shift, we estimate the Rb-3He spin-exchange cross section. The Rb EPR frequency shift, which is 53 kHz for a 100% polarized 10-amagat 3He sample at 50 °C, can be used to determine the absolute polarization of nuclear polarized 3He targets. From these measurements, one can also predict the shift of the 3He NMR line due to a polarized Rb vapor.https://resolver.caltech.edu/CaltechAUTHORS:NEWpra93Atom galleries for whispering atoms: binding atoms in stable orbits around an optical resonator
https://resolver.caltech.edu/CaltechAUTHORS:MABol94
Year: 1994
The external fields of optical whispering gallery modes may be used to confine atoms in stable orbits around
a dielectric microsphere. As an example, a toroidal dipole-force trap (atom gallery) for three-level atoms is
investigated, and the possibility of achieving an atomic (matter-wave) resonator is discussed. The extremely
small electromagnetic mode volumes and high Q's of the whispering gallery modes should permit a circulating
photon to be repeatedly absorbed and reemitted by a trapped whispering atom.https://resolver.caltech.edu/CaltechAUTHORS:MABol94Blue-light induced infrared absorption in KNbO3
https://resolver.caltech.edu/CaltechAUTHORS:MABjosab94
Year: 1994
We have used a high-finesse cavity to measure the cw intensity dependence and dynamics of blue-light-induced infrared absorption (BLIIRA) in KNbO3 crystals for blue-light intensities between 7 x 10^-4 and 2 x 10^4 W/cm^2. We discuss the detrimental effects of BLIIRA on the efficiency of intracavity frequency doubling and the threshold for parametric oscillation.https://resolver.caltech.edu/CaltechAUTHORS:MABjosab94Inversion of quantum jumps in quantum optical systems under continuous observation
https://resolver.caltech.edu/CaltechAUTHORS:MABprl96
Year: 1996
DOI: 10.1103/PhysRevLett.76.3108
We formulate conditions for invertibility of quantum jumps in systems that decay by emission of quanta into a continuously monitored reservoir. We propose proof-of-principle experiments using techniques from cavity quantum electrodynamics and ion trapping, and briefly discuss the relevance of such methods for error correction in quantum computation.https://resolver.caltech.edu/CaltechAUTHORS:MABprl96Real-time detection of individual atoms falling through a high-finesse optical cavity
https://resolver.caltech.edu/CaltechAUTHORS:MABol96
Year: 1996
The enhanced coupling between atoms and photons inside a high-finesse optical cavity provides a novel basis for optical measurements that continuously monitor atomic degrees of freedom. We describe an experiment in which cavity quantum-electrodynamic effects are utilized for real-time detection of individual atoms falling through an optical cavity after being dropped from a magneto-optical trap. Our technique permits experiments that are triggered by the presence of a single optimally coupled atom within the cavity mode volume.https://resolver.caltech.edu/CaltechAUTHORS:MABol96Dynamical identification of open quantum systems
https://resolver.caltech.edu/CaltechAUTHORS:MABqso96
Year: 1996
DOI: 10.1088/1355-5111/8/6/002
I propose a quantum-trajectories approach to parametric identification of the effective Hamiltonian for a Markovian open quantum system, and discuss an application motivated by recent experiments in cavity quantum electrodynamics. This example illustrates a strategy for quantum parameter estimation that efficiently utilizes the information carried by correlations between measurements distributed in time.https://resolver.caltech.edu/CaltechAUTHORS:MABqso96High-Q measurements of fused-silica microspheres in the near infrared
https://resolver.caltech.edu/CaltechAUTHORS:VERol98
Year: 1998
Measurements of the quality factor Q ~ 8 x 10^9 are reported for the whispering-gallery modes (WGM's) of quartz microspheres for the wavelengths 670, 780, and 850 nm; these results correspond to finesse F ~ 2.2 x 10^6. The observed independence of Q from wavelength indicates that losses for the WGM's are dominated by a mechanism other than bulk absorption in fused silica in the near infrared. Data obtained by atomic force microscopy combined with a simple model for surface scattering suggest that Q can be limited by residual surface inhomogeneities. Absorption by absorbed water can also explain why the material limit is not reached at longer wavelengths in the near infrared.https://resolver.caltech.edu/CaltechAUTHORS:VERol98Standard quantum limits for broadband position measurement
https://resolver.caltech.edu/CaltechAUTHORS:MABpra98
Year: 1998
DOI: 10.1103/PhysRevA.58.123
I utilize the Caves-Milburn model for continuous position measurements to formulate a broadband version of the standard quantum limit (SQL) for monitoring the position of a free mass and illustrate the use of Kalman filtering to recover the SQL for estimating a weak classical force that acts on a quantum-mechanical test particle under continuous observation. These derivations are intended to clarify the interpretation of SQL's in the context of broadband quantum measurement, with particular attention paid to the question of how it might be possible to verify that a given laboratory measurement does indeed achieve backaction-limited sensitivity. The method used to analyze force detection may be extended to the case of weak classical forces with arbitrary time dependence, including nonstationary and impulsive signals.https://resolver.caltech.edu/CaltechAUTHORS:MABpra98Retroactive Quantum Jumps in a Strongly Coupled Atom-Field System
https://resolver.caltech.edu/CaltechAUTHORS:MABprl98
Year: 1998
DOI: 10.1103/PhysRevLett.81.4620
We investigate a novel type of conditional dynamic that occurs in the strongly driven Jaynes-Cummings system with dissipation. Extending the work of Alsing and Carmichael [Quantum Opt. 3, 13 (1991)], we present a combined numerical and analytic study of the stochastic master equation that describes the system's conditional evolution when the cavity output is continuously observed via homodyne detection, but atomic spontaneous emission is not monitored at all. We find that quantum jumps of the atomic state are induced by its dynamical coupling to the optical field, in order retroactively to justify atypical fluctuations occurring in the homodyne photocurrent.https://resolver.caltech.edu/CaltechAUTHORS:MABprl98Quantum manipulation and measurement of single atoms in optical cavity QED
https://resolver.caltech.edu/CaltechAUTHORS:YEJieeetim99
Year: 1999
DOI: 10.1109/19.769669
Using laser-cooled atoms strongly coupled to a high finesse optical cavity, we have performed real-time continuous measurements of single atomic trajectories in terms of the interaction energy (Eint) with the cavity. Individual transit events reveal a shot-noise limited measurement (fractional) sensitivity of 4×10-4/√Hz to variations in Eint/ℏ within a bandwidth of 1300 kHz. The strong coupling of atom and cavity leads to a maximum interaction energy greater than the kinetic energy of an intracavity laser-cooled atom, even under weak cavity excitation. Evidence of mechanical light forces for intracavity photon number <1 has been observed. The quantum character of the nonlinear optical response of the atom-cavity system is manifested for the trajectory of a single atom.https://resolver.caltech.edu/CaltechAUTHORS:YEJieeetim99Quantum feedback control and classical control theory
https://resolver.caltech.edu/CaltechAUTHORS:DOHpra00
Year: 2000
DOI: 10.1103/PhysRevA.62.012105
We introduce and discuss the problem of quantum feedback control in the context of established formulations of classical control theory, examining conceptual analogies and essential differences. We describe the application of state-observer-based control laws, familiar in classical control theory, to quantum systems and apply our methods to the particular case of switching the state of a particle in a double-well potential.https://resolver.caltech.edu/CaltechAUTHORS:DOHpra00A sub-Doppler resolution double resonance molecular beam infrared spectrometer operating at chemically relevant energies (~2 eV)
https://resolver.caltech.edu/CaltechAUTHORS:SRIrsi00
Year: 2000
DOI: 10.1063/1.1310343
A molecular beam spectrometer capable of achieving sub-Doppler resolution at 2 eV (~18 000 cm^–1) of vibrational excitation is described and its performance demonstrated using the CH stretch chromophore of HCN. Two high finesse resonant power-buildup cavities are used to excite the molecules using a sequential double resonance technique. A v = 0-->2 transition is first saturated using a 1.5 µm color center laser, whereupon a fraction of the molecules is further excited to the v = 6 level using an amplitude modulated Ti:Al2O3 laser. The energy absorbed by the molecules is detected downstream of both excitation points by a cryogenically cooled bolometer using phase sensitive detection. A resolution of approximately 15 MHz (i.e., three parts in 10^8) is demonstrated by recording a rotational line in the v = 6 manifold of HCN. Scan speeds of up to several cm^–1/h were obtained, with signal-to-noise ratios in excess of 100. The high signal-to-noise ratio and a dynamic range of 6×10^4 means that future experiments to study statistical intramolecular vibrational energy redistribution in small molecules and unimolecular isomerizations can be attempted. We would also like to point out that, with improved metrology in laser wavelengths, this instrument can also be used to provide improved secondary frequency standards based upon the rovibrational spectra of molecules.https://resolver.caltech.edu/CaltechAUTHORS:SRIrsi00Rovibrational spectroscopy of the v = 6 manifold in 12C2H2 and 13C2H2
https://resolver.caltech.edu/CaltechAUTHORS:SRIjcp00
Year: 2000
DOI: 10.1063/1.1310605
We recorded rovibrational spectra of the 006+ level of 12C2H2 and the 2131 11–1 level of 13C2H2 in the ground electronic state using a two-photon sequential double resonance technique with a resolution of 15 MHz. Owing to the g/u symmetry of acetylene, the levels that we observe are inaccessible from the ground state by single photon techniques, and observation of these levels is reported here for the first time. Upper state rotational constants were derived from whole band fits of the observed lines, and compare favorably with expected values. Both spectra exhibit signs of local perturbations, and a density of states analysis leads us to believe that we are observing couplings to the full density of vibrational states one would expect from acetylene in this energy region. Despite the high resolution of our spectrometer, and the high excitation energy, no evidence for acetylene hydrogen permutation exchange isomerization (which is predicted to proceed through the vinylidene minimum on the potential) has been observed, implying that the rate of exchange isomerization is more than four orders-of-magnitude below the rate predicted by RRKM (Rice, Ramsperger, Kassel, and Marcus) theory.https://resolver.caltech.edu/CaltechAUTHORS:SRIjcp00Sensitivity optimization in quantum parameter estimation
https://resolver.caltech.edu/CaltechAUTHORS:VERpra01
Year: 2001
DOI: 10.1103/PhysRevA.64.032111
We present a general framework for sensitivity optimization in quantum parameter estimation schemes based on continuous (indirect) observation of a dynamical system. As an illustrative example, we analyze the canonical scenario of monitoring the position of a free mass or harmonic oscillator to detect weak classical forces. We show that our framework allows the consideration of sensitivity scheduling, as well as estimation strategies for nonstationary signals, leading us to propose corresponding generalizations of the standard quantum limit for force detection.https://resolver.caltech.edu/CaltechAUTHORS:VERpra01Design of photonic crystal microcavities for cavity QED
https://resolver.caltech.edu/CaltechAUTHORS:VUCpre02
Year: 2002
DOI: 10.1103/PhysRevE.65.016608
We discuss the optimization of optical microcavity designs based on two-dimensional photonic crystals for the purpose of strong coupling between the cavity field and a single neutral atom trapped within a hole. We present numerical predictions for the quality factors and mode volumes of localized defect modes as a function of geometric parameters, and discuss some experimental challenges related to the coupling of a defect cavity to gas-phase atoms.https://resolver.caltech.edu/CaltechAUTHORS:VUCpre02Quantum-Classical Transition in Nonlinear Dynamical Systems
https://resolver.caltech.edu/CaltechAUTHORS:HABprl02
Year: 2002
DOI: 10.1103/PhysRevLett.88.040402
Viewed as approximations to quantum mechanics, classical evolutions can violate the positive semidefiniteness of the density matrix. The nature of the violation suggests a classification of dynamical systems based on classical-quantum correspondence; we show that this can be used to identify when environmental interaction (decoherence) will be unsuccessful in inducing the quantum-classical transition. In particular, the late-time Wigner function can become positive without any corresponding approach to classical dynamics. In the light of these results, we emphasize key issues relevant for experiments studying the quantum-classical transition.https://resolver.caltech.edu/CaltechAUTHORS:HABprl02Quantum trajectories for realistic detection
https://resolver.caltech.edu/CaltechAUTHORS:WARpra02
Year: 2002
DOI: 10.1103/PhysRevA.65.023802
Quantum trajectories describe the stochastic evolution of an open quantum system conditioned on continuous monitoring of its output, such as, by an ideal photodetector. Here we derive (non-Markovian) quantum trajectories for realistic photodetection, including the effects of efficiency, dead time, bandwidth, electronic noise, and dark counts. We apply our theory to a realistic cavity QED scenario and investigate the impact of such detector imperfections on the conditional evolution of the system state. A practical theory of quantum trajectories with realistic detection will be essential for experimental and technological applications of quantum feedback in many areas.https://resolver.caltech.edu/CaltechAUTHORS:WARpra02Optimization of the Q factor in photonic crystal microcavities
https://resolver.caltech.edu/CaltechAUTHORS:VUCieeejqe02
Year: 2002
DOI: 10.1109/JQE.2002.1017597
We express the quality factor of a mode in terms of the Fourier transforms of its field components and prove that the reduction in radiation loss can be achieved by suppressing the mode's wavevector components within the light cone. Although this is intuitively clear, our analytical proof gives us insight into how to achieve the Q factor optimization, without the mode delocalization. We focus on the dipole defect mode in free-standing membranes and achieve Q > 10^4, while preserving the mode volume of the order of one half of the cubic wavelength of light in the material. The derived expressions and conclusions can be used in the optimization of the Q factor for any type of defect in planar photonic crystals.https://resolver.caltech.edu/CaltechAUTHORS:VUCieeejqe02Photon Statistics and Dynamics of Fluorescence Resonance Energy Transfer
https://resolver.caltech.edu/CaltechAUTHORS:BERprl02
Year: 2002
DOI: 10.1103/PhysRevLett.89.068101
We report high time-resolution measurements of photon statistics from pairs of dye molecules coupled by fluorescence resonance energy transfer (FRET). In addition to quantum-optical photon antibunching, we observe photon bunching on a time scale of several nanoseconds. We show by numerical simulation that configuration fluctuations in the coupled fluorophore system could account for minor deviations of our data from predictions of basic Förster theory. With further characterization we believe that FRET photon statistics could provide a unique tool for studying DNA mechanics on time scales from 10^-9 – 10^-3 s.https://resolver.caltech.edu/CaltechAUTHORS:BERprl02Exact performance of concatenated quantum codes
https://resolver.caltech.edu/CaltechAUTHORS:RAHpra02
Year: 2002
DOI: 10.1103/PhysRevA.66.032304
When a logical qubit is protected using a quantum error-correcting code, the net effect of coding, decoherence (a physical channel acting on qubits in the codeword) and recovery can be represented exactly by an effective channel acting directly on the logical qubit. In this paper we describe a procedure for deriving the map between physical and effective channels that results from a given coding and recovery procedure. We show that the map for a concatenation of codes is given by the composition of the maps for the constituent codes. This perspective leads us to an efficient means for calculating the exact performance of quantum codes with arbitrary levels of concatenation. We present explicit results for single-bit Pauli channels. For certain codes under the symmetric depolarizing channel, we use the coding maps to compute exact threshold error probabilities for achievability of perfect fidelity in the infinite concatenation limit.https://resolver.caltech.edu/CaltechAUTHORS:RAHpra02Adaptive Homodyne Measurement of Optical Phase
https://resolver.caltech.edu/CaltechAUTHORS:ARMprl02
Year: 2002
DOI: 10.1103/PhysRevLett.89.133602
We present an experimental demonstration of the power of feedback in quantum metrology, confirming the predicted [H. M. Wiseman, Phys. Rev. Lett. 75, 4587 (1995)] superior performance of an adaptive homodyne technique for single-shot measurement of optical phase. For measurements performed on weak coherent states with no prior knowledge of the signal phase, adaptive homodyne estimation approaches closer to the intrinsic quantum uncertainty than any previous technique. Our results underscore the importance of real-time feedback for reaching quantum limits in measurement and control.https://resolver.caltech.edu/CaltechAUTHORS:ARMprl02Cavity Quantum Electrodynamics: Coherence in Context
https://resolver.caltech.edu/CaltechAUTHORS:20141112-143838015
Year: 2002
DOI: 10.1126/science.1078446
Modern cavity quantum electrodynamics (cavity QED) illuminates the most fundamental aspects of coherence and decoherence in quantum mechanics. Experiments on atoms in cavities can be described by elementary models but reveal intriguing subtleties of the interplay of coherent dynamics with external couplings. Recent activity in this area has pioneered powerful new approaches to the study of quantum coherence and has fueled the growth of quantum information science. In years to come, the purview of cavity QED will continue to grow as researchers build on a rich infrastructure to attack some of the most pressing open questions in micro- and mesoscopic physics.https://resolver.caltech.edu/CaltechAUTHORS:20141112-143838015Programmable logic devices in experimental quantum optics
https://resolver.caltech.edu/CaltechAUTHORS:STOjosab02
Year: 2002
We discuss the unique capabilities of programmable logic devices (PLDs) for experimental quantum optics and describe basic procedures of design and implementation. Examples of advanced applications include optical metrology and feedback control of quantum dynamical systems. As a tutorial illustration of the PLD implementation process, a field-programmable gate array controller is used to stabilize the output of a Fabry-Perot cavity.https://resolver.caltech.edu/CaltechAUTHORS:STOjosab02Inverse-problem approach to designing photonic crystals for cavity QED experiments
https://resolver.caltech.edu/CaltechAUTHORS:GERpre02
Year: 2002
DOI: 10.1103/PhysRevE.66.066606
Photonic band gap (PBG) materials are attractive for cavity QED experiments because they provide extremely small mode volumes and are monolithic, integratable structures. As such, PBG cavities are a promising alternative to Fabry-Perot resonators. However, the cavity requirements imposed by QED experiments, such as the need for high Q (low cavity damping) and small mode volumes, present significant design challenges for photonic band gap materials. Here, we pose the PBG design problem as a mathematical inversion and provide an analytical solution for a two-dimensional (2D) crystal. We then address a planar (2D crystal with finite thickness) structure using numerical techniques.https://resolver.caltech.edu/CaltechAUTHORS:GERpre02Characterizing the entanglement of symmetric many-particle spin-1/2 systems
https://resolver.caltech.edu/CaltechAUTHORS:STOpra03
Year: 2003
DOI: 10.1103/PhysRevA.67.022112
Analyzing the properties of entanglement in many-particle spin-1/2 systems is generally difficult because the system's Hilbert space grows exponentially with the number of constituent particles, N. Fortunately, it is still possible to investigate a many-particle entanglement when the state of the system possesses sufficient symmetry. In this paper, we present a practical method for efficiently computing various bipartite entanglement measures for states in the symmetric subspace and perform these calculations for N similar to 10^(3). By considering all possible bipartite splits, we construct a picture of the multiscale entanglement in large symmetric systems. In particular, we characterize dynamically generated spin-squeezed states by comparing them to known reference states (e.g., Greenberger-Horne-Zeilinger and Dicke states), and families of states with near-maximal bipartite entropy. We quantify the trade-off between the degree of entanglement and its robustness to particle loss, emphasizing that substantial entanglement need not be fragile.https://resolver.caltech.edu/CaltechAUTHORS:STOpra03Quantum jumps between dressed states: A proposed cavity-QED test using feedback
https://resolver.caltech.edu/CaltechAUTHORS:REIpra03
Year: 2003
DOI: 10.1103/PhysRevA.67.042106
A strongly driven cavity containing a single resonant strongly coupled atom exhibits a phase bistability. The phase of the field is strongly correlated with the phase of the atomic dipole. It has been shown previously that phase-sensitive monitoring of the field emitted by the cavity would induce conditional quantum jumps between orthogonal atomic dipole states ("dressed" states). Here we show that such monitoring can be used to fix the atom into a single dressed state. As soon as a state-changing quantum jump is inferred from the measurement of the field, the atomic state is flipped using a π pulse. We study this feedback scheme analytically and numerically. We show that the occupation probability of the desired fixed state can be as high as 1-1/8ηC1, where C1≫1 is the single-atom cooperativity and η the detection efficiency (which does not have to be close to unity). The control of the atomic dynamics is manifest in the fluorescence spectrum. The widths of all three peaks are modified from the usual Mollow spectrum, and almost all of the area under one of the sidebands is transferred to the other sideband. This is as expected, as one of the dressed states is essentially unoccupied, and transitions out of it do not occur. In addition, the width of the central peak goes to zero. This indicates coherent scattering due to the nonzero mean atomic dipole created by the feedback.https://resolver.caltech.edu/CaltechAUTHORS:REIpra03Atom mirror etched from a hard drive
https://resolver.caltech.edu/CaltechAUTHORS:LEVapl03
Year: 2003
DOI: 10.1063/1.1592305
We describe the fabrication of an atom mirror by etching of a common hard drive, and we report the observation of specular retroreflection of 11 muK cesium atoms using this mirror. The atoms were trapped and cooled above the hard drive using the mirror magneto-optical trap technique, and upon release, two full bounces were detected. The hard drive atom mirror will be a useful tool for both atom optics and quantum computation.https://resolver.caltech.edu/CaltechAUTHORS:LEVapl03Quantum Kalman filtering and the Heisenberg limit in atomic magnetometry
https://resolver.caltech.edu/CaltechAUTHORS:GERprl03
Year: 2003
DOI: 10.1103/PhysRevLett.91.250801
The shot-noise detection limit in current high-precision magnetometry [I. Kominis, T. Kornack, J. Allred, and M. Romalis, Nature (London) 422, 596 (2003)] is a manifestation of quantum fluctuations that scale as 1/root-N in an ensemble of N atoms. Here, we develop a procedure that combines continuous measurement and quantum Kalman filtering [V. Belavkin, Rep. Math. Phys. 43, 405 (1999)] to surpass this conventional limit by exploiting conditional spin squeezing to achieve 1/N field sensitivity. Our analysis demonstrates the importance of optimal estimation for high bandwidth precision magnetometry at the Heisenberg limit and also identifies an approximate estimator based on linear regression.https://resolver.caltech.edu/CaltechAUTHORS:GERprl03Robust quantum parameter estimation: Coherent magnetometry with feedback
https://resolver.caltech.edu/CaltechAUTHORS:STOpra04b
Year: 2004
DOI: 10.1103/PhysRevA.69.032109
We describe the formalism for optimally estimating and controlling both the state of a spin ensemble and a scalar magnetic field with information obtained from a continuous quantum limited measurement of the spin precession due to the field. The full quantum parameter estimation model is reduced to a simplified equivalent representation to which classical estimation and control theory is applied. We consider both the tracking of static and fluctuating fields in the transient and steady-state regimes. By using feedback control, the field estimation can be made robust to uncertainty about the total spin number.https://resolver.caltech.edu/CaltechAUTHORS:STOpra04bQuantum feedback control of atomic motion in an optical cavity
https://resolver.caltech.edu/CaltechAUTHORS:STEprl04
Year: 2004
DOI: 10.1103/PhysRevLett.92.223004
We study quantum feedback cooling of atomic motion in an optical cavity. We design a feedback algorithm that can cool the atom to the ground state of the optical potential with high efficiency despite the nonlinear nature of this problem. An important ingredient is a simplified state-estimation algorithm, necessary for a real-time implementation of the feedback loop. We also describe the critical role of parity dynamics in the cooling process and present a simple theory that predicts the achievable steady-state atomic energies.https://resolver.caltech.edu/CaltechAUTHORS:STEprl04Deterministic Dicke-state preparation with continuous measurement and control
https://resolver.caltech.edu/CaltechAUTHORS:STOpra04
Year: 2004
DOI: 10.1103/PhysRevA.70.022106
We characterize the long-time projective behavior of the stochastic master equation describing a continuous, collective spin measurement of an atomic ensemble both analytically and numerically. By adding state-based feedback, we show that it is possible to prepare highly entangled Dicke states deterministically.https://resolver.caltech.edu/CaltechAUTHORS:STOpra04A new approach to teaching feedback
https://resolver.caltech.edu/CaltechAUTHORS:MURieeecsm04
Year: 2004
DOI: 10.1109/MCS.2004.1337856
The Control and Dynamical Systems (CDS) Department at the California Institute of Technology (Caltech) has revised its entry-level curriculum in dynamics, feedback, and control with the goals of updating the subject matter to include modern tools and making control tools accessible to a nontraditional audience. One of the approaches made was to divide the introductory control theory class into two tracks, with a conceptual track geared toward students who need only a conceptual overview of control tools and an analytical track providing a more detailed mathematical treatment of feedback. The conceptual track, CDS 101, which is mainly discussed in the paper, is intended for advanced students in science and engineering who can benefit from an overview of control techniques but who might not have the need for the mathematical depth underlying the material. Special attention is paid to ensuring that the course is accessible to students from biological, physical, and information sciences, using examples from these domains to illustrate concepts. The goal of the course is to enable students to use the principles and tools of feedback in their research activities.https://resolver.caltech.edu/CaltechAUTHORS:MURieeecsm04Proposed magnetoelectrostatic ring trap for neutral atoms
https://resolver.caltech.edu/CaltechAUTHORS:HOPpra04
Year: 2004
DOI: 10.1103/PhysRevA.70.053616
We propose a trap for confining cold neutral atoms in a microscopic ring using a magnetoelectrostatic potential. The trapping potential is derived from a combination of a repulsive magnetic field from a hard drive atom mirror and the attractive potential produced by a charged disk patterned on the hard drive surface. We calculate a trap frequency of [29.7,42.6,62.8] kHz and a depth of [16.1,21.8,21.8] MHz for [Cs-133, Rb-87, K-40], and discuss a simple loading scheme and a method for fabrication. This device provides a one-dimensional potential in a ring geometry that may be of interest to the study of trapped quantum degenerate one-dimensional gases.https://resolver.caltech.edu/CaltechAUTHORS:HOPpra04Suppression of spin projection noise in broadband atomic magnetometry
https://resolver.caltech.edu/CaltechAUTHORS:GERprl05
Year: 2005
DOI: 10.1103/PhysRevLett.94.203002
We demonstrate that quantum nondemolition measurement, combined with a suitable parameter estimation procedure, can improve the sensitivity of a broadband atomic magnetometer by reducing uncertainty due to spin projection noise. Furthermore, we provide evidence that real-time quantum feedback control offers robustness to classical uncertainties, including shot-to-shot atom number fluctuations, that would otherwise prevent quantum-limited performance.https://resolver.caltech.edu/CaltechAUTHORS:GERprl05Feedback control of quantum state reduction
https://resolver.caltech.edu/CaltechAUTHORS:VANieeetac05
Year: 2005
DOI: 10.1109/TAC.2005.849193
Feedback control of quantum mechanical systems must take into account the probabilistic nature of quantum measurement. We formulate quantum feedback control as a problem of stochastic nonlinear control by considering separately a quantum filtering problem and a state feedback control problem for the filter. We explore the use of stochastic Lyapunov techniques for the design of feedback controllers for quantum spin systems and demonstrate the possibility of stabilizing one outcome of a quantum measurement with unit probability.https://resolver.caltech.edu/CaltechAUTHORS:VANieeetac05Quantum projection filter for a highly nonlinear model in cavity QED
https://resolver.caltech.edu/CaltechAUTHORS:HANjob05a
Year: 2005
DOI: 10.1088/1464-4266/7/10/005
Both in classical and quantum stochastic control theory a major role is played by the filtering equation, which recursively updates the information state of the system under observation. Unfortunately, the theory is plagued by infinite dimensionality of the information state which severely limits its practical applicability, except in a few select cases (e.g. the linear Gaussian case). One solution proposed in classical filtering theory is that of the projection filter. In this scheme, the filter is constrained to evolve in a finite-dimensional family of densities through orthogonal projection on the tangent space with respect to the Fisher metric. Here we apply this approach to the simple but highly nonlinear quantum model of optical phase bistability of a strongly coupled two-level atom in an optical cavity. We observe near-optimal performance of the quantum projection filter, demonstrating the utility of such an approach.https://resolver.caltech.edu/CaltechAUTHORS:HANjob05aModelling and feedback control design for quantum state preparation
https://resolver.caltech.edu/CaltechAUTHORS:HANjob05b
Year: 2005
DOI: 10.1088/1464-4266/7/10/001
The goal of this article is to provide a largely self-contained introduction to the modelling of controlled quantum systems under continuous observation, and to the design of feedback controls that prepare particular quantum states. We describe a bottom-up approach, where a field-theoretic model is subjected to statistical inference and is ultimately controlled. As an example, the formalism is applied to a highly idealized interaction of an atomic ensemble with an optical field. Our aim is to provide a unified outline for the modelling, from first principles, of realistic experiments in quantum control.https://resolver.caltech.edu/CaltechAUTHORS:HANjob05bTracking-FCS: Fluorescence correlation spectroscopy of individual particles
https://resolver.caltech.edu/CaltechAUTHORS:BERoe05
Year: 2005
We exploit recent advances in single-particle tracking to perform fluorescence correlation spectroscopy on individual fluorescent particles, in contrast to traditional methods that build up statistics over a sequence of many measurements. By rapidly scanning the focus of an excitation laser in a circular pattern, demodulating the measured fluorescence, and feeding these results back to a piezoelectric translation stage, we track the Brownian motion of fluorescent polymer microspheres in aqueous solution in the plane transverse to the laser axis. We discuss the estimation of particle diffusion statistics from closed-loop position measurements, and we present a generalized theory of fluorescence correlation spectroscopy for the case that the motion of a single fluorescent particle is actively tracked by a time-dependent laser intensity. We model the motion of a tracked particle using Ornstein-Uhlenbeck statistics, using a general theory that contains a umber of existing results as specific cases. We find good agreement between our theory and experimental results, and discuss possible future applications of these techniques to passive, single-shot, single-molecule fluorescence measurements with many orders of magnitude in time resolution.https://resolver.caltech.edu/CaltechAUTHORS:BERoe05Tensor polarizability and dispersive quantum measurement of multilevel atoms
https://resolver.caltech.edu/CaltechAUTHORS:GERpra06
Year: 2006
DOI: 10.1103/PhysRevA.73.042112
Optimally extracting information from measurements performed on a physical system requires an accurate model of the measurement interaction. Continuously probing the collective spin of an alkali-metal atom cloud via its interaction with an off-resonant optical probe is an important example of such a measurement where realistic modeling at the quantum level is possible using standard techniques from atomic physics. Typically, however, tutorial descriptions of this technique have neglected the multilevel structure of realistic atoms for the sake of simplification. We account for the full multilevel structure of alkali-metal atoms and derive the irreducible form of the polarizability Hamiltonian describing a typical dispersive quantum measurement. For a specific set of parameters, we then show that semiclassical predictions of the theory are consistent with our experimental observations of polarization scattering by a polarized cloud of laser-cooled cesium atoms. We also derive the signal-to-noise ratio under a single-measurement trial and use this to predict the rate of spin squeezing with multilevel alkali-metal atoms for arbitrary detuning of the probe beam.https://resolver.caltech.edu/CaltechAUTHORS:GERpra06Low-lying bifurcations in cavity quantum electrodynamics
https://resolver.caltech.edu/CaltechAUTHORS:ARMpra06
Year: 2006
DOI: 10.1103/PhysRevA.73.063801
The interplay of quantum fluctuations with nonlinear dynamics is a central topic in the study of open quantum systems, connected to fundamental issues (such as decoherence and the quantum-classical transition) and practical applications (such as coherent information processing and the development of mesoscopic sensors and amplifiers). With this context in mind, we here present a computational study of some elementary bifurcations that occur in a driven and damped cavity quantum electrodynamics (cavity QED) model at low intracavity photon number. In particular, we utilize the single-atom cavity QED master equation and associated stochastic Schrödinger equations to characterize the equilibrium distribution and dynamical behavior of the quantized intracavity optical field in parameter regimes near points in the semiclassical (mean-field, Maxwell-Bloch) bifurcation set. Our numerical results show that the semiclassical limit sets are qualitatively preserved in the quantum stationary states, although quantum fluctuations apparently induce phase diffusion within periodic orbits and stochastic transitions between attractors. We restrict our attention to an experimentally realistic parameter regime.https://resolver.caltech.edu/CaltechAUTHORS:ARMpra06Feedback cooling of atomic motion in cavity QED
https://resolver.caltech.edu/CaltechAUTHORS:STEpra06
Year: 2006
DOI: 10.1103/PhysRevA.74.012322
We consider the problem of controlling the motion of an atom trapped in an optical cavity using continuous feedback. In order to realize such a scheme experimentally, one must be able to perform state estimation of the atomic motion in real time. While in theory this estimate may be provided by a stochastic master equation describing the full dynamics of the observed system, integrating this equation in real time is impractical. Here we derive an approximate estimation equation for this purpose, and use it as a drive in a feedback algorithm designed to cool the motion of the atom. We examine the effectiveness of such a procedure using full simulations of the cavity QED system, including the quantized motion of the atom in one dimension.https://resolver.caltech.edu/CaltechAUTHORS:STEpra06Finesse and sensitivity gain in cavity-enhanced absorption spectroscopy of biomolecules in solution
https://resolver.caltech.edu/CaltechAUTHORS:MCGoe06
Year: 2006
We describe a 'wet mirror' apparatus for cw cavity-enhanced absorption measurements with Bacteriochlorophyll a (BChla) in solution and show that it achieves the full sensitivity gain (≈ 2.3×10^4) afforded by the finesse (3.4 × 10^4) and loss distribution of our optical resonator. This result provides an important proof-of-principle demonstration for solution-phase cavity-enhanced spectroscopy; straightforward extrapolation to a system with state-of-the-art low-loss mirrors and shot-noise-limited performance indicates that single molecule sensitivity in liquids is within reach of current technology. With the probe laser locked to the cavity resonance, our instrument achieves a sensitivity ≈3.4×10^−8/√Hz (for a sample of length 1.75 mm) with 100 kHz bandwidth and can reliably detect sub-nM concentrations of BChla with 1 ms integration time.https://resolver.caltech.edu/CaltechAUTHORS:MCGoe06Feedback localization of freely diffusing fluorescent particles near the optical shot-noise limit
https://resolver.caltech.edu/CaltechAUTHORS:BERol07
Year: 2007
We report near-optimal tracking of freely diffusing fluorescent particles in a quasi-two-dimensional geometry via photon counting and real-time feedback. We present a quantitative statistical model of our feedback network and find excellent agreement with the experiment. We monitor the motion of a single fluorescent particle with a sensitivity of 15 nm/sqrt Hz while collecting fewer than 5000 fluorescence photons/s. Fluorescent microspheres (diffusion coefficient 1.3 μm^2/s) are tracked with a root-mean-square tracking error of 170 nm, within a factor of 2 of the theoretical limit set by photon counting shot noise.https://resolver.caltech.edu/CaltechAUTHORS:BERol07Scattering of polarized laser light by an atomic gas in free space: A quantum stochastic differential equation approach
https://resolver.caltech.edu/CaltechAUTHORS:BOUpra07
Year: 2007
DOI: 10.1103/PhysRevA.75.052111
We propose a model, based on a quantum stochastic differential equation (QSDE), to describe the scattering of polarized laser light by an atomic gas. The gauge terms in the QSDE account for the direct scattering of the laser light into different field channels. Once the model has been set, we can rigorously derive quantum filtering equations for balanced polarimetry and homodyne detection experiments, study the statistics of output processes, and investigate a strong driving, weak coupling limit.https://resolver.caltech.edu/CaltechAUTHORS:BOUpra07Fluctuations in closed-loop fluorescent particle tracking
https://resolver.caltech.edu/CaltechAUTHORS:BERoe07
Year: 2007
We present a comprehensive theory of closed-loop particle tracking for calculating the statistics of a diffusing fluorescent particle's motion relative to the tracking lock point. A detailed comparison is made between the theory and experimental results, with excellent quantitative agreement found in all cases. A generalization of the theory of (open-loop) fluorescence correlation spectroscopy is developed, and the relationship to previous results is discussed. Two applications of the statistical techniques are given: a method for determining a tracked particle's localization and an algorithm for rapid particle classification based on real-time analysis of the tracking control signal.https://resolver.caltech.edu/CaltechAUTHORS:BERoe07Physical model of continuous two-qubit parity measurement in a cavity-QED network
https://resolver.caltech.edu/CaltechAUTHORS:20090813-082319568
Year: 2009
DOI: 10.1103/PhysRevA.79.024305
We propose and analyze a physical implementation of two-qubit parity measurements as required for continuous error correction, assuming a setup in which the individual qubits are strongly coupled to separate optical cavities. A single optical probe beam scatters sequentially from the two cavities, and the continuous parity measurement is realized via fixed quadrature homodyne photodetection. We present models based on quantum stochastic differential equations (QSDEs) for both an ideal continuous parity measurement and our proposed cavity quantum electrodynamics (cavity QED) implementation; a recent adiabatic elimination theorem for QSDEs is used to assert strong convergence of the latter to the former in an appropriate limit of physical parameters. Performance of the cavity QED scheme is studied via numerical simulation with experimentally realistic parameters.https://resolver.caltech.edu/CaltechAUTHORS:20090813-082319568Quantum filter reduction for measurement-feedback control via unsupervised manifold learning
https://resolver.caltech.edu/CaltechAUTHORS:20091120-151421650
Year: 2009
DOI: 10.1088/1367-2630/11/10/105043
We derive simple models for the dynamics of a single atom coupled to a cavity field mode in the absorptive bistable parameter regime by projecting the time evolution of the state of the system onto a suitably chosen nonlinear low-dimensional manifold, which is found by use of local tangent space alignment. The output field from the cavity is detected with a homodyne detector allowing observation of quantum jumps of the system between states with different average numbers of photons in the cavity. We find that the models, which are significantly faster to integrate numerically than the full stochastic master equation, largely reproduce the dynamics of the system, and we demonstrate that they are sufficiently accurate to facilitate feedback control of the state of the system based on the predictions of the models alone.https://resolver.caltech.edu/CaltechAUTHORS:20091120-151421650Spontaneous Dressed-State Polarization in the Strong Driving Regime of Cavity QED
https://resolver.caltech.edu/CaltechAUTHORS:20091111-100654288
Year: 2009
DOI: 10.1103/PhysRevLett.103.173601
We utilize high-bandwidth phase-quadrature homodyne measurement of the light transmitted through a Fabry-Perot cavity, driven strongly and on resonance, to detect excess phase noise induced by a single intracavity atom. We analyze the correlation properties and driving-strength dependence of the atom-induced phase noise to establish that it corresponds to the long-predicted phenomenon of spontaneous dressed-state polarization. Our experiment thus provides a demonstration of cavity quantum electrodynamics in the strong-driving regime in which one atom interacts strongly with a many-photon cavity field to produce novel quantum stochastic behavior.https://resolver.caltech.edu/CaltechAUTHORS:20091111-100654288A fully programmable 100-spin coherent Ising machine with all-to-all connections
https://resolver.caltech.edu/CaltechAUTHORS:20180608-163642732
Year: 2016
DOI: 10.1126/science.aah5178
Unconventional, special-purpose machines may aid in accelerating the solution of some of the hardest problems in computing, such as large-scale combinatorial optimizations, by exploiting different operating mechanisms than those of standard digital computers. We present a scalable optical processor with electronic feedback that can be realized at large scale with room-temperature technology. Our prototype machine is able to find exact solutions of, or sample good approximate solutions to, a variety of hard instances of Ising problems with up to 100 spins and 10,000 spin-spin connections.https://resolver.caltech.edu/CaltechAUTHORS:20180608-163642732Reduced models and design principles for half-harmonic generation in synchronously pumped optical parametric oscillators
https://resolver.caltech.edu/CaltechAUTHORS:20180608-163041953
Year: 2016
DOI: 10.1103/PhysRevA.94.063809
We develop reduced models that describe half-harmonic generation in a synchronously pumped optical parametric oscillator above threshold, where nonlinearity, dispersion, and group-velocity mismatch are all relevant. These models are based on (1) an eigenmode expansion for low pump powers, (2) a simultonlike sech-pulse ansatz for intermediate powers, and (3) dispersionless box-shaped pulses for high powers. Analytic formulas for pulse compression, degenerate vs nondegenerate operation, and stability are derived and compared to numerical and experimental results.https://resolver.caltech.edu/CaltechAUTHORS:20180608-163041953