Advantages of Coherent Feedback for Cooling Quantum Oscillators

TL;DR

This paper demonstrates that coherent feedback control schemes can outperform measurement-based methods in cooling quantum oscillators, leveraging all-optical feedback to achieve lower excitation levels.

Contribution

It introduces a modeling framework for optical feedback in quantum resonators and shows the advantages of coherent feedback over measurement-based control in the quantum regime.

Findings

Coherent feedback outperforms measurement-based schemes in low excitation regimes.

All-optical feedback enables processing of non-commuting quadratures without fidelity loss.

Performance gains suggest new directions for nonlinear and robust quantum control.

Abstract

We model the cooling of open optical and optomechanical resonators via optical feedback in the Linear Quadratic Gaussian setting of stochastic control theory. We show that coherent feedback control schemes, in which the resonator is embedded in an interferometer to achieve all-optical feedback, can outperform the best possible measurement-based schemes in the quantum regime of low steady-state excitation number. Such performance gains are attributed to the coherent controller's ability to process non-commuting output field quadratures simultaneously without loss of fidelity, and may provide important clues for the design of coherent feedback schemes for more general problems of nonlinear and robust control.