Real-time Information, Uncertainty and Quantum Feedback Control

TL;DR

This paper compares coherent and measurement-based quantum feedback control protocols, highlighting their differences in real-time information use and ability to handle parameter uncertainty, with measurement-based control often performing better.

Contribution

It establishes an equivalent relationship between quantum CFC and non-selective quantum MFC, and demonstrates that quantum MFC can outperform CFC in certain stabilization and uncertainty scenarios.

Findings

Quantum MFC can better stabilize quantum states.

Quantum MFC handles Hamiltonian parameter uncertainty more effectively.

An equivalence between quantum CFC and non-selective quantum MFC is established.

Abstract

Feedback is the core concept in cybernetics and its effective use has made great success in but not limited to the fields of engineering, biology, and computer science. When feedback is used to quantum systems, two major types of feedback control protocols including coherent feedback control (CFC) and measurement-based feedback control (MFC) have been developed. In this paper, we compare the two types of quantum feedback control protocols by focusing on the real-time information used in the feedback loop and the capability in dealing with parameter uncertainty. An equivalent relationship is established between quantum CFC and non-selective quantum MFC in the form of operator-sum representation. Using several examples of quantum feedback control, we show that quantum MFC can theoretically achieve better performance than quantum CFC in stabilizing a quantum state and dealing with Hamiltonian parameter uncertainty. The results enrich understanding of the relative advantages between quantum MFC and quantum CFC, and can provide useful information in choosing suitable feedback protocols for quantum systems.