# Distributed Quantum Metrology with a Single Squeezed-Vacuum Source

## TL;DR

This paper introduces a quantum metrology scheme that achieves Heisenberg-limited sensitivity for estimating multiple phase delays using only a single squeezed vacuum source, antisqueezing, and simple detectors, avoiding complex entangled states.

## Contribution

It presents a novel interferometric protocol for multi-parameter phase estimation that requires minimal quantum resources and no entangled or photon-number resolving detectors.

## Key findings

- Achieves Heisenberg-limited sensitivity for multiple phase parameters.
- Requires only a single squeezed vacuum source and simple detection methods.
- Eliminates the need for entangled states or complex auxiliary channels.

## Abstract

We propose an interferometric scheme for the estimation of a linear combination with non-negative weights of an arbitrary number $M>1$ of unknown phase delays, distributed across an $M$-channel linear optical network, with Heisenberg-limited sensitivity. This is achieved without the need of any sources of photon-number or entangled states, photon-number resolving detectors or auxiliary interferometric channels. Indeed, the proposed protocol remarkably relys upon a single squeezed state source, an antisqueezing operation at the interferometer output, and on-off photodetectors.