New fundamental limits on design and control of linear quantum systems are presented. A main difference between quantum and classical systems comes from the fact that quantum signals are represented by operator-valued vectors. The transfer function representation is useful to describe a system in the quantum setting for the same reason as it is useful classically. It is shown that the noncommutative property of quantum signals can be characterized by a specific relation between zeros and poles of a quantum transfer function. Then, two quantum mechanical tradeoffs follows from the transfer function constraint. One is a well known tradeoff, Heisenberg’s uncertainty relation, and the other is a tradeoff between the ability of noise reduction and sensitivity to modeling error. While these tradeoffs hold at each frequency, quantum systems have another constraint between different frequencies based on Bode integral as classical systems usually do. In the quantum case, however, this constraint is also dependent on quantum mechanical parameters.
New fundamental limits on design and control of linear quantum systems are presented. A main difference between quantum and classical systems comes from the fact that quantum signals are represented by operator-valued vectors. The transfer function representation is useful to describe a system in the quantum setting for the same reason as it is useful classically. It is shown that the noncommutative property of quantum signals can be characterized by a specific relation between zeros and poles of a quantum transfer function. Then, two quantum mechanical tradeoffs follows from the transfer function constraint. One is a well known tradeoff, Heisenberg’s uncertainty relation, and the other is a tradeoff between the ability of noise reduction and sensitivity to modeling error. While these tradeoffs hold at each frequency, quantum systems have another constraint between different frequencies based on Bode integral as classical systems usually do. In the quantum case, however, this constraint is also dependent on quantum mechanical parameters.
The non-commutative nature of quantum mechanics imposes fundamental constraints on system dynamics, which, in the linear realm, are manifested through the physical realizability conditions on system matrices. These restrictions give system matrices a unique structure. This paper aims to study this structure by investigating the zeros and poles of linear quantum systems. Firstly, it is shown that −s0 is a transmission zero if and only if s0 is a pole of the transfer function, and −s0 is an invariant zero if and only if s0 is an eigenvalue of the A-matrix, of a linear quantum system. Moreover, s0 is an output-decoupling zero if and only if −s0 is an input-decoupling zero. Secondly, based on these pole-zero correspondences and inspired by a recent work on the stable inversion of classical linear systems \cite{DD2023}, we show that a linear quantum system must be Hurwitz unstable if it is strongly asymptotically left invertible. Two types of stable input observers are constructed for unstable linear quantum systems. Finally, the sensitivity of a coherent feedback network is investigated; in particular, the fundamental tradeoff between ideal squeezing and system robustness is studied on the basis of system sensitivity analysis.
The non-commutative nature of quantum mechanics imposes fundamental constraints on system dynamics, which, in the linear realm, are manifested through the physical realizability conditions on system matrices. These restrictions give system matrices a unique structure. This paper aims to study this structure by investigating the zeros and poles of linear quantum systems. Firstly, it is shown that−s0is a transmission zero if and only ifs0is a pole of the transfer function, and−s0is an invariant zero if and only ifs0is an eigenvalue of theA-matrix, of a linear quantum system. Moreover,s0is an output-decoupling zero if and only if−s0is an input-decoupling zero. Secondly, based on these pole-zero correspondences and inspired by a recent work on the stable inversion of classical linear systems [1], we show that a linear quantum system must be Hurwitz unstable if it is strongly asymptotically left invertible. Two types of stable input observers are constructed for unstable linear quantum systems. Finally, the sensitivity of a coherent feedback network is investigated; in particular, the fundamental tradeoff between ideal squeezing and system robustness is studied on the basis of system sensitivity analysis.
The non-commutative nature of quantum mechanics imposes fundamental constraints on system dynamics, which in the linear realm are manifested by the physical realizability conditions on system matrices. These restrictions endow system matrices with special structure. The purpose of this paper is to study such structure by investigating zeros and poses of linear quantum systems. In particular, we show that −s0∗ is a transmission zero if and only if s0 is a pole, and which is further generalized to the relationship between system eigenvalues and invariant zeros. Additionally, we study left-invertibility and fundamental tradeoff for linear quantum systems in terms of their zeros and poles.
Some models of linear control system schemas are developed here for quantum linear systems. The most important linear devices in quantum optics are introduced with their differential equations. These linear quantum systems are zero-order and first-order transfer functions with one pole and one zero. We mathematical compute transfer function of different interconnections by using zero-order and first-order systems. for instance, by designing series and feedback interconnection, we will obtain higher-order quantum linear systems. Also, we will analyze a closed-loop feedback of a first-order linear quantum system containing a gain in feedback path
We derive the quantum stochastic master equation for bosonic systems without measurement theory but control theory. It is shown that the quantum effect of the measurement can be represented as the correlation between dynamical and measurement noise. The transfer function representation allows us to analyze a dynamical uncertainty relation which imposes strong constraints on the dynamics of the linear quantum systems. In particular, quantum systems preserving the minimum uncertainty are uniquely determined. For large spin systems, it is shown that local dynamics are equivalent to bosonic systems. Considering global behavior, we find quantum effects to which there is no classical counterparts. A control problem of producing maximal entanglement is discussed as the stabilization of a filtering process.
We study continuous variable systems, in which quantum and classical degrees of freedom are combined and treated on the same footing. Thus all systems, including the inputs or outputs to a channel, may be quantum-classical hybrids. This allows a unified treatment of a large variety of quantum operations involving measurements or dependence on classical parameters. The basic variables are given by canonical operators with scalar commutators. Some variables may commute with all others and hence generate a classical subsystem. We systematically study the class of "quasifree" operations, which are characterized equivalently either by an intertwining condition for phase-space translations or by the requirement that, in the Heisenberg picture, Weyl operators are mapped to multiples of Weyl operators. This includes the well-known Gaussian operations, evolutions with quadratic Hamiltonians, and "linear Bosonic channels", but allows for much more general kinds of noise. For example, all states are quasifree. We sketch the analysis of quasifree preparation, measurement, repeated observation, cloning, teleportation, dense coding, the setup for the classical limit, and some aspects of irreversible dynamics, together with the precise salient tradeoffs of uncertainty, error, and disturbance. Although the spaces of observables and states are infinite dimensional for every non-trivial system that we consider, we treat the technicalities related to this in a uniform and conclusive way, providing a calculus that is both easy to use and fully rigorous.