Balanced-heterodyne detection of sub-shot-noise optical signals

TL;DR

This paper analyzes a balanced heterodyne detection scheme for sub-shot-noise optical signals, highlighting how squeezed states improve signal-to-noise ratio and proposing a phase-locking method for practical implementation, with potential applications in gravitational-wave detection.

Contribution

It provides a detailed spectral density analysis of the heterodyne scheme and introduces a phase-locking technique to enhance practical feasibility.

Findings

Maximal SNR enhancement requires signals in the squeezed quadrature.

The scheme can eliminate additional heterodyne noise.

Proposed phase-locking technique demonstrates practical feasibility.

Abstract

As part of the effort to make use of squeezed states of light for detection of sub-shot-noise optical signals, we study the balanced heterodyne scheme, for which the corresponding spectral density of the photocurrent fluctuations produced at the output of the detector is calculated as the Fourier transform of their autocorrelation function. Our analysis shows that, for maximal signal-to-noise ratio enhancement by use of squeezed states of light, an optical signal to be measured must be carried in the squeezed quadrature of the carrier field. We discuss how "the additional heterodyne noise" can be eliminated in this scheme and its potential application to gravitational-wave searching. To demonstrate the practical feasibility, we propose and study a phase-locking technique for this scheme.