Toward Heisenberg-Limited Interferometry with Dual Squeezers

TL;DR

This paper proposes a dual-squeezing scheme in Mach-Zehnder interferometry that achieves Heisenberg-limited phase sensitivity with direct photon detection, overcoming previous fundamental limitations.

Contribution

Introducing a dual-squeezing approach with an additional squeezer before detection to enable Heisenberg-limited sensitivity with direct detection.

Findings

Achieves Heisenberg scaling in phase sensitivity.

Remains robust against detection noise.

Overcomes divergence issues at optimal equal intensities.

Abstract

The canonical Mach-Zehnder interferometer fed with a coherent state and a squeezed-vacuum state of equal intensities is theoretically predicted to achieve Heisenberg scaling in phase sensitivity. However, this ultimate performance is unattainable using direct photon-number-difference detection due to a divergence arising precisely at the optimal equal-intensity regime. In this work, we introduce a dual-squeezing approach that overcomes this fundamental limitation. Our scheme employs an additional single-mode squeezer before detection, forming a paired configuration with the input squeezer used to generate the squeezed-vacuum state. We analytically demonstrate that the resulting dual-squeezing Mach-Zehnder interferometer enables Heisenberg-limited phase sensitivity with di rect photon-number-difference detection, while remaining robust against detection noise. Our work provides a feasible and robust route toward quantum-limited interferometric phase measurements