Sensitivity Analysis of Cascaded Quantum Feedback Amplifier

TL;DR

This paper analyzes the sensitivity of cascaded quantum feedback amplifiers, comparing series connection and single feedback control, demonstrating that single feedback offers better robustness against uncertainties through theoretical proof and numerical simulations.

Contribution

It extends quantum feedback control theory to cascaded amplifiers, showing that single feedback control improves sensitivity over series configurations.

Findings

Single feedback control reduces sensitivity to uncertainties.

Theoretical proof supports better robustness of single feedback.

Numerical simulations confirm improved performance.

Abstract

Quantum amplifier is an essential device in quantum information processing. As in the classical (non-quantum) case, its characteristic uncertainty needs to be suppressed by feedback, and in fact such a control theory for a single quantum amplifier has recently been developed. This letter extends this result to the case of cascaded quantum amplifier. In particular, we consider two types of structures: the case where controlled amplifiers are connected in series, and the case where a single feedback control is applied to the cascaded amplifier. Then, we prove that the latter is better in the sense of sensitivity to the uncertainty. A detailed numerical simulation is given to show actual performance of these two feedback schemes.