An Exponential Quantum Projection Filter for Open Quantum Systems

TL;DR

This paper introduces an exponential quantum projection filter for open quantum systems, reducing computational complexity by constraining quantum trajectories to a finite-dimensional manifold, with proven stability and demonstrated effectiveness through simulations.

Contribution

It develops a novel exponential quantum projection filtering scheme using differential geometry, simplifying quantum filter equations and enabling more efficient quantum control.

Findings

Significant reduction in computational cost compared to traditional quantum filters

Proven input-to-state stability for systems converging to pure states

Simulation results demonstrate effective performance in atomic ensemble systems

Abstract

An approximate exponential quantum projection filtering scheme is developed for a class of open quantum systems described by Hudson- Parthasarathy quantum stochastic differential equations, aiming to reduce the computational burden associated with online calculation of the quantum filter. By using a differential geometric approach, the quantum trajectory is constrained in a finite-dimensional differentiable manifold consisting of an unnormalized exponential family of quantum density operators, and an exponential quantum projection filter is then formulated as a number of stochastic differential equations satisfied by the finite-dimensional coordinate system of this manifold. A convenient design of the differentiable manifold is also presented through reduction of the local approximation errors, which yields a simplification of the quantum projection filter equations. It is shown that the computational cost can be significantly reduced by using the quantum projection filter instead of the quantum filter. It is also shown that when the quantum projection filtering approach is applied to a class of open quantum systems that asymptotically converge to a pure state, the input-to-state stability of the corresponding exponential quantum projection filter can be established. Simulation results from an atomic ensemble system example are provided to illustrate the performance of the projection filtering scheme. It is expected that the proposed approach can be used in developing more efficient quantum control methods.