Reframing SU(1,1) interferometry

TL;DR

This paper analyzes SU(1,1) interferometry, revealing its fundamental mechanisms and its relation to active squeezing and back-action-evading measurements, providing insights into its operation and potential applications.

Contribution

It offers a detailed breakdown of SU(1,1) interferometry, connecting it to active squeezing and phase-space displacement detection, and introduces a simplified prototype for disturbance detection.

Findings

SU(1,1) interferometry is a two-mode active-squeezing process.

Truncating the interferometer yields a prototype for disturbance detection.

Entanglement of two-mode squeezing is key to measurement sensitivity.

Abstract

SU(1,1) interferometry, proposed in a classic 1986 paper by Yurke, McCall, and Klauder [Phys. Rev. A 33, 4033 (1986)], involves squeezing, displacing, and then unsqueezing two bosonic modes. It has, over the past decade, been implemented in a variety of experiments. Here I take SU(1,1) interferometry apart, to see how and why it ticks. SU(1,1) interferometry arises naturally as the two-mode version of active-squeezing-enhanced, back-action-evading measurements aimed at detecting the phase-space displacement of a harmonic oscillator subjected to a classical force. Truncating an SU(1,1) interferometer, by omitting the second two-mode squeezer, leaves a prototype that uses the entanglement of two-mode squeezing to detect and characterize a disturbance on one of the two modes from measurement statistics gathered from both modes.