Entanglement-assisted quantum feedback control

TL;DR

This paper introduces an entanglement-assisted feedback control method for linear quantum systems, demonstrating improved estimation and control performance, notably in cooling opto-mechanical oscillators beyond classical limits.

Contribution

It develops a novel entanglement-based feedback control approach for quantum systems, enhancing estimation accuracy and control efficiency over existing methods.

Findings

Entanglement reduces estimation error in quantum feedback control.

Entanglement-assisted control lowers the stationary occupation number of an oscillator.

The method outperforms controllers using coherent or squeezed probe fields.

Abstract

The main advantage of quantum metrology relies on the effective use of entanglement, which indeed allows us to achieve strictly better estimation performance over the standard quantum limit. In this paper, we propose an analogous method uti- lizing entanglement for the purpose of feedback control. The system considered is a general linear dynamical quantum system, where the control goal can be systemati- cally formulated as a linear quadratic Gaussian control problem based on the quantum Kalman filtering method; in this setting, an entangled input probe field is effectively used to reduce the estimation error and accordingly the control cost function. In par- ticular, we show that, in the problem of cooling an opto-mechanical oscillator, the entanglement-assisted feedback control can lower the stationary occupation number of the oscillator below the limit attainable by the controller with a coherent probe field and furthermore beats the controller with an optimized squeezed probe field.