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

Howard M. Wiseman; Andrew C. Doherty

doi:10.1117/12.547492

25 May 2004 Open quantum systems with linear dynamics: optimal unravellings for optimal feedback control

Proceedings Volume 5468, Fluctuations and Noise in Photonics and Quantum Optics II; (2004) https://doi.org/10.1117/12.547492
Event: Second International Symposium on Fluctuations and Noise, 2004, Maspalomas, Gran Canaria Island, Spain

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) 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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Howard M. Wiseman and Andrew C. Doherty "Open quantum systems with linear dynamics: optimal unravellings for optimal feedback control", Proc. SPIE 5468, Fluctuations and Noise in Photonics and Quantum Optics II, (25 May 2004); https://doi.org/10.1117/12.547492

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KEYWORDS

Control systems

Feedback control

Stochastic processes

Quantum physics

Diffusion

Matrices

Virtual colonoscopy

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