Optimal quantum-enhanced interferometry using a laser power source

TL;DR

This paper determines the optimal quantum state for enhancing interferometer sensitivity with a laser power source, finding that squeezed vacuum states maximize phase measurement precision under photon number constraints.

Contribution

It identifies squeezed vacuum as the optimal input state for quantum-enhanced interferometry with a laser source, based on the quantum Cramér-Rao bound.

Findings

Squeezed vacuum states optimize phase sensitivity.

Quantum Cramér-Rao bound guides the optimal state selection.

Provides practical guidance for high-sensitivity interferometry.

Abstract

We consider an interferometer powered by laser light (a coherent state) into one input port and ask the following question: what is the best state to inject into the second input port, given a constraint on the mean number of photons this state can carry, in order to optimize the interferometer's phase sensitivity? This question is the practical question for high-sensitivity interferometry. We answer the question by considering the quantum Cram{\'e}r-Rao bound for such a setup. The answer is squeezed vacuum.