arXiv subjects

Shanon L. Vuglar

Publications and source records attributed to Shanon L. Vuglar.

7 recordsLinked to original sources

arXiv2023

A Coherent LQG approach to Quantum Equalization

We propose a method to design a suboptimal, coherent quantum LQG controller to solve a quantum equalization problem. Our method involves reformulating the problem as a control problem and then designing a classical LQG controller and implementing it as a quantum system. Illustrative examples are included which demonstrate the algorithm for both active and passive systems, i.e., systems where the dynamics are described in terms of both position and momentum operators and systems with dynamics in terms of annihilation operators only.

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arXiv2022

A J-spectral Factorization Condition for the Physical Realizability of a Transfer Function Matrix with only Direct Feedthrough Quantum Noise

This paper gives a J-spectral factorization condition for the implementation of a strictly proper transfer function matrix as a physically realizable quantum system using only direct feedthrough quantum noise. A necessary frequency response condition is also presented. Examples are included to illustrate the main results.

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arXiv2018

Non-conservative Forces via Quantum Reservoir Engineering

A systematic approach is given for engineering dissipative environments that steer quantum wavepackets along desired trajectories. The methodology is demonstrated with several illustrative examples: environment-assisted tunneling, trapping, effective mass assignment, and pseudo-relativistic behavior. Non-conservative stochastic forces do not inevitably lead to decoherence - we show that purity can be well-preserved. These findings highlight the flexibility offered by non-equilibrium open quantum dynamics.

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arXiv2015

Design of coherent quantum observers for linear quantum systems

Quantum versions of control problems are often more difficult than their classical counterparts because of the additional constraints imposed by quantum dynamics. For example, the quantum LQG and quantum H infinity optimal control problems remain open. To make further progress, new, systematic and tractable methods need to be developed. This paper gives three algorithms for designing coherent observers, i.e., quantum systems that are connected to a quantum plant and their outputs provide information about the internal state of the plant. Importantly, coherent observers avoid measurements of the plant outputs. We compare our coherent observers with a classical (measurement-based) observer by way of an example involving an optical cavity with thermal and vacuum noises as inputs.

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arXiv2015

Quantum Noises, Physical Realizability and Coherent Quantum Feedback Control

Physical Realizability addresses the question of whether it is possible to implement a given linear time invariant (LTI) system as a quantum system. A given synthesized quantum controller described by a set of stochastic differential equations does not necessarily correspond to a physically meaningful quantum system. However, if additional quantum noises are permitted in the implementation, it is always possible to implement an arbitrary LTI system as a quantum system. In this paper, we give an expression for the number of introduced noise channels required to implement a given LTI system as a quantum system. We then consider the special case where only the transfer function to be implemented is of interest. We give results showing when it is possible to implement a transfer function as a quantum system by introducing the same number of quantum noises as there are system outputs. Finally, we demonstrate the utility of these results by providing an algorithm for obtaining a suboptimal solution to a coherent quantum LQG control problem.

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arXiv2013

Quantum Implemention of an LTI System with the minimal number of additional quantum noise inputs

Physical Realizability addresses the question of whether it is possible to implement a given LTI system as a quantum system. It is in general not true that a given synthesized quantum controller described by a set of stochastic differential equations is equivalent to some physically meaningful quantum system. However, if additional quantum noises are permitted in the implementation it is always possible to implement an arbitrary LTI system as a quantum system. In this paper we give an expression for the exact number of noises required to implement a given LTI system as a quantum system. Furthermore, we focus our attention on proving that this is a minimum, that is, it is not possible to implement the system as a quantum system with a smaller number of additional quantum noises.

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arXiv2012

Singular Perturbation Approximations for General Linear Quantum Systems

This paper considers the use of singular perturbation approximations for general linear quantum systems where the system dynamics are described in terms of both annihilation and creation operators. Results that are related to the physical realizability property of the approximate system are presented.

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