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  • Open quantum systems with linear dynamics: optimal unravellings for optimal feedback control

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    Author(s)
    Wiseman, HM
    Doherty, AC
    Griffith University Author(s)
    Wiseman, Howard M.
    Year published
    2004
    Metadata
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    Abstract
    Quantum feedback control is the control of the dynamics of a quantum system by feeding back (in real time) the results of monitoring that system. For systems with linear dynamics, the control problem is amenable to exact analysis. In these cases, the quantum system is equivalent to a stochastic system of classical phase-space variables with linear drift and constant diffusion, and with a measured current (e.g. a homodyne photocurrent) linear in the system variables. However, the classical evolution is constrained in order to represent valid quantum evolution. We quantify this in terms of a linear matrix inequality (LMI) ...
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    Quantum feedback control is the control of the dynamics of a quantum system by feeding back (in real time) the results of monitoring that system. For systems with linear dynamics, the control problem is amenable to exact analysis. In these cases, the quantum system is equivalent to a stochastic system of classical phase-space variables with linear drift and constant diffusion, and with a measured current (e.g. a homodyne photocurrent) linear in the system variables. However, the classical evolution is constrained in order to represent valid quantum evolution. We quantify this in terms of a linear matrix inequality (LMI) relating the drift and diffusion (a sort of zero temperature fluctuation-dissipation theorem), and another LMI for the covariance matrix of the possible conditioned states (i.e. under all possible monitoring schemes consistent with the master equation). For manipulable systems (i.e. where the experimenter has arbitrary control over the parameters in a Hamiltonian linear in the system variables) the covariance of the conditioned state is all that is needed to calculate the effectiveness of the feedback. In this case the double optimization problem reduces to a semidefinite program, which can be solved efficiently in general. We illustrate this with an example drawn from quantum optics.
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    Conference Title
    FLUCTUATIONS AND NOISE IN PHOTONICS AND QUANTUM OPTICS II
    Volume
    5468
    Publisher URI
    http://spiedl.org/dbt/dbt.jsp?KEY=PSISDG&Volume=5468&Issue=1&bproc=symp&scode=FN04
    DOI
    https://doi.org/10.1117/12.547492
    Copyright Statement
    © 2004 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
    Subject
    Quantum physics not elsewhere classified
    Publication URI
    http://hdl.handle.net/10072/26025
    Collection
    • Conference outputs

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