Precise quantum control via unsharp measurements and feedback operations

TL;DR

This paper introduces a universal quantum control scheme using unsharp measurements and feedback to eliminate noise effects, maintaining high-fidelity dynamics across various system dimensions.

Contribution

The proposed measurement-feedback method effectively suppresses noise-induced errors in quantum systems of any dimension, enhancing control precision.

Findings

Successfully eliminates trajectory errors caused by static and non-static noises

Maintains high-fidelity quantum dynamics in two-level and multi-level systems

The scheme's effectiveness depends on noise and measurement strengths

Abstract

In this paper, we propose a scheme to eliminate the influence of noises on system dynamics, by means of a sequential unsharp measurements and unitary feedback operations. The unsharp measurements are carried out periodically during system evolution, while the feedback operations are well designed based on the eigenstates of the density matrices of the exact (noiseless) dynamical states and its corresponding post-measurement states. For illustrative examples, we show that the dynamical trajectory errors caused by both static and non-static noises are successfully eliminated in typical two-level and multi-level systems, i.e., the high-fidelity quantum dynamics can be maintained. Furthermore, we discuss the influence of noise strength and measurement strength on the degree of precise quantum control. Crucially, the measurement-feedback scheme is quite universal in that it can be applied to precise quantum control for any dimension systems. Thus, it naturally finds extensive applications in quantum information processing.