1,624 research outputs found
Real-time detection of individual atoms falling through a high-finesse optical cavity
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
Quantum Trajectories for Realistic Detection
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.Comment: 5 pages, 4 figures (3 .eps included, 1 jpeg as an additional file).
To be published in Phys. Rev.
Design of nanophotonic circuits for autonomous subsystem quantum error correction
We reapply our approach to designing nanophotonic quantum memories to
formulate an optical network that autonomously protects a single logical qubit
against arbitrary single-qubit errors. Emulating the 9 qubit Bacon-Shor
subsystem code, the network replaces the traditionally discrete syndrome
measurement and correction steps by continuous, time-independent optical
interactions and coherent feedback of unitarily processed optical fields.Comment: 12 pages, 4 figure
A new bound of the ℒ2[0, T]-induced norm and applications to model reduction
We present a simple bound on the finite horizon ℒ2/[0, T]-induced norm of a linear time-invariant (LTI), not necessarily stable system which can be efficiently computed by calculating the ℋ∞ norm of a shifted version of the original operator. As an application, we show how to use this bound to perform model reduction of unstable systems over a finite horizon. The technique is illustrated with a non-trivial physical example relevant to the appearance of time-irreversible phenomena in statistical physics
A new approach to teaching feedback
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
Quantum feedback control and classical control theory
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
Retroactive quantum jumps in a strongly-coupled atom-field system
We investigate a novel type of conditional dynamic that occurs in the
strongly-driven Jaynes-Cummings model with dissipation. Extending the work of
Alsing and Carmichael [Quantum Opt. {\bf 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 in ocurring in the homodyne photocurrent.Comment: 4 pages, uses RevTex, 5 EPS figure
Partial melting and segregation behavior in a superplastic Si3N4/Al-Mg alloy composite
科研費報告書収録論文(課題番号:07455252・基盤研究(B)(2)・H7~H9/研究代表者:小池, 淳一/αTi-Al固溶体における異常高温強化
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