Effects of losses on the sensitivity of an actively correlated Mach-Zehnder interferometer

TL;DR

This paper analyzes how losses affect the phase sensitivity of an actively correlated Mach-Zehnder interferometer, proposing optimization strategies to maintain quantum advantage despite losses.

Contribution

It introduces a theoretical framework for phase sensitivity in ACMZI under losses and suggests gain adjustments to preserve quantum-enhanced sensitivity.

Findings

ACMZI can beat SQL in low-loss conditions

Sensitivity decreases with increasing losses

Gain tuning can mitigate sensitivity loss

Abstract

We theoretically studied the quantum Cram\'{e}r-Rao bound of an actively correlated Mach-Zehnder interferometer (ACMZI), where the quantum Fisher information obtained by the phase-averaging method can give the proper phase-sensing limit without any external phase reference. We numerically calculate the phase sensitivities with the method of homodyne detection and intensity detection in the presence of losses. Under lossless and very low loss conditions, the ACMZI is operated in a balanced case to beat the standard quantum limit (SQL). As the loss increases, the reduction in sensitivity increases. However within a certain range, we can adjust the gain parameters of the beam recombination process to reduce the reduction in sensitivity and realize the sensitivity can continue to beat the SQL in an unbalanced situation. Our scheme provides an optimization method of phase estimation in the presence of losses.