Quantum Feedback Cooling without State Filtering

TL;DR

This paper presents a quantum feedback control method that stabilizes quantum states without full state estimation, using simple measurement filtering to enable scalable cooling strategies.

Contribution

It introduces an output-based feedback approach that approximates state-based control, avoiding complex real-time quantum state estimation.

Findings

Numerical demonstrations show effective cooling performance.

The method simplifies implementation by using measurement filtering.

It enables scalable quantum cooling without full state estimation.

Abstract

We introduce a state-based feedback law that stabilizes quantum states or subspaces associated with extremal values of a continuously monitored observable - a problem motivated by quantum cooling tasks. We then propose an output-based approximation that uses simple filtering of the measurement record to emulate the required feedback signal, thereby avoiding full real-time quantum state estimation, a key bottleneck for implementing and scaling filtering-based feedback control. The performance of the resulting strategy is demonstrated numerically on two test-bed models for feedback cooling.