Nearly Optimal Measurement Scheme in a Noisy Mach-Zehnder Interferometer with Coherent and Squeezed Vacuum

TL;DR

This paper evaluates various measurement schemes in a noisy Mach-Zehnder interferometer using coherent and squeezed vacuum states, identifying near-optimal strategies under different noise conditions for ultra-precise parameter estimation.

Contribution

It compares the performance of measurement schemes like intensity, parity, and homodyne detection under realistic noise conditions, highlighting the robustness of homodyne detection.

Findings

Intensity measurement beats shot-noise limit at low power

Homodyne detection remains near optimal under noise

Parity measurement is optimal without noise

Abstract

The use of an interferometer to perform an ultra-precise parameter estimation under noisy conditions is a challenging task. Here we discuss nearly optimal measurement schemes for a well known,sensitive input state, squeezed vacuum and coherent light. We find that a single mode intensity measurement, while the simplest and able to beat the shot-noise limit, is outperformed by other measurement schemes in the low-power regime. However, at high powers, intensity measurement is only outperformed by a small factor. Specifically, we confirm, that an optimal measurement choice under lossless conditions is the parity measurement. In addition, we also discuss the performance of several other common measurement schemes when considering photon loss, detector efficiency, phase drift, and thermal photon noise. We conclude that, with noise considerations, homodyne remains near optimal in both the low and high power regimes. Surprisingly, some of the remaining investigated measurement schemes, including the previous optimal parity measurement, do not remain even near optimal when noise is introduced.