Absolute Measurement of Quantum-Limited Interferometric Displacements

TL;DR

This paper presents a straightforward method for absolute, quantum-limited measurement of tiny interferometric displacements using high-frequency modulation, enabling detection at the fundamental quantum limit without assumptions on the light source.

Contribution

It introduces a novel high-frequency optical path modulation technique for quantum-limited displacement measurements in interferometry.

Findings

Achieves measurement at the quantum Cramér-Rao limit.

Method is simple and easily implementable.

Provides full characterization of displacement from harmonic phase information.

Abstract

A methodology is introduced that enables an absolute, quantum-limited measurement of sub-wavelength interferometric displacements. The technique utilizes a high-frequency optical path modulation within an interferometer operated in a homodyne configuration. All of the information necessary to fully characterize the resultant path displacement is contained within the relative strengths of the various harmonics of the phase modulation. The method, which is straightforward and readily implementable, allows a direct measurement of the theoretical Cram\'er-Rao limit of detection without any assumptions on the nature of the light source.