Phase estimation with squeezed single photons

TL;DR

This paper investigates the use of squeezed single photons in interferometry, demonstrating conditions under which they outperform squeezed vacuum states in quantum Fisher information and sensitivity, even with non-ideal detectors.

Contribution

It introduces a comparative analysis of squeezed single photons versus squeezed vacuum in interferometry, highlighting thresholds for improved performance based on squeezing and photon number.

Findings

Squeezed single photons outperform squeezed vacuum in quantum Fisher information above certain thresholds.

Enhanced sensitivity achievable with squeezed single photons when specific squeezing parameters are met.

Performance advantage persists even with non-unit quantum efficiency.

Abstract

We address the performance of an interferometric setup in which a squeezed single photon interferes at a beam splitter with a coherent state. Our analysis in based on both the quantum Fisher information and the sensitivity when a Mach-Zehnder setup is considered and the difference photocurrent is detected at the output. We compare our results with those obtained feeding the interferometer with a squeezed vacuum (with the same squeezing parameter of the squeezed single photon) and a coherent state in order to have the same total number of photons circulating in the interferometer. We find that for fixed squeezing parameter and total number of photons there is a threshold of the coherent amplitude interfering with the squeezed single photon above which the squeezed single photons outperform the performance of squeezed vacuum (showing the highest quantum Fisher information). When the difference photocurrent measurement is considered, we can always find a threshold of the squeezing parameter (given the total number of photons and the coherent amplitude) above which squeezed single photons can be exploited to reach a better sensitivity with respect to the use of squeezed vacuum states also in the presence of non unit quantum efficiency.