Replacing measurement feedback with coherent feedback for quantum state preparation

TL;DR

This paper demonstrates that in quantum state preparation, classical measurement feedback can be replaced by a fully quantum coherent feedback mechanism, enabling autonomous dissipation into target states without classical intervention.

Contribution

It introduces a quantum coherent feedback method that replaces classical measurement feedback in quantum state preparation, improving robustness and autonomy.

Findings

Coherent feedback achieves state stabilization similar to measurement feedback.

The method applies to qubit, qutrit, spin squeezing, and Fock state generation.

Quantum feedback reduces practical imperfections inherent in classical feedback.

Abstract

Measurement feedback is a versatile and powerful tool, although its performance is limited by several practical imperfections resulting from classical components. This paper shows that, for some typical quantum feedback control problems for state preparation (stabilization of a qubit or a qutrit, spin squeezing, and Fock state generation), the classical feedback operation can be replaced by a fully quantum one such that the state autonomously dissipates into the target or a state close to the target. The main common feature of the proposed quantum operation, which is called coherent feedback, is that it is composed of a series of dispersive and dissipative couplings inspired by the corresponding measurement feedback scheme.