Revisiting Quantum Feedback Control: Disentangling the Feedback-induced Phase from the Corresponding Amplitude

TL;DR

This paper explores controlling the feedback phase in quantum systems using a microwave pump, enhancing feedback protocols by manipulating phase shifts in a three-level system.

Contribution

It introduces a method to control feedback phase via a microwave pump, enabling on-demand phase shifts in quantum feedback control.

Findings

Microwave pump induces controllable phase shifts in feedback signals.

Enhanced quantum feedback control protocols through phase manipulation.

Demonstration using a three-level quantum system.

Abstract

Coherent time-delayed feedback allows the control of a quantum system and its partial stabilization against noise and decoherence. The crucial and externally accessible parameters in such control setups are the round-trip-induced delay time $\tau$ and the frequencies $\omega$ of the involved optical transitions which are typically controllable via global parameters like temperature, bias or strain. They influence the dynamics via the amplitude and the phase $\phi = \omega \tau$ of the feedback signal. These quantities are, however, not independent. Here, we propose to control the feedback phase via a microwave pump field. Using the example of a $\Lambda$-type three-level system, we show that the Rabi frequency of the pump field induces phase shifts on demand and therefore increases the applicability of coherent quantum feedback control protocols.