Generation of $^{87}$Rb-resonant bright two-mode squeezed light with four-wave mixing

TL;DR

This paper demonstrates the generation of narrow-band, two-mode squeezed light resonant with $^{87}$Rb atomic transitions using four-wave mixing in hot $^{85}$Rb, achieving significant intensity difference squeezing levels for quantum metrology applications.

Contribution

It introduces a method to produce two-mode squeezed states resonant with $^{87}$Rb transitions via four-wave mixing in $^{85}$Rb, enabling enhanced atomic sensor sensitivity.

Findings

Achieved -3.5 dB intensity difference squeezing with both modes on resonance.

Enhanced squeezing of -5.4 dB and -5.0 dB when only one mode is resonant.

Generated narrow-band squeezed light suitable for atomic quantum metrology.

Abstract

Squeezed states of light have found their way into a number of applications in quantum-enhanced metrology due to their reduced noise properties. In order to extend such an enhancement to metrology experiments based on atomic ensembles, an efficient light-atom interaction is required. Thus, there is a particular interest in generating narrow-band squeezed light that is on atomic resonance. This will make it possible not only to enhance the sensitivity of atomic based sensors, but also to deterministically entangle two distant atomic ensembles. We generate bright two-mode squeezed states of light, or twin beams, with a non-degenerate four-wave mixing (FWM) process in hot $^{85}$Rb in a double-lambda configuration. Given the proximity of the energy levels in the D1 line of $^{85}$Rb and $^{87}$Rb, we are able to operate the FWM in $^{85}$Rb in a regime that generates two-mode squeezed states in which both modes are simultaneously on resonance with transitions in the D1 line of $^{87}$Rb, one mode with the $F=2$ to $F'=2$ transition and the other one with the $F=1$ to $F'=1$ transition. For this configuration, we obtain an intensity difference squeezing level of $-3.5$ dB. Moreover, the intensity difference squeezing increases to $-5.4$ dB and $-5.0$ dB when only one of the modes of the squeezed state is resonant with the D1 $F=2$ to $F'=2$ or $F=1$ to $F'=1$ transition of $^{87}$Rb, respectively.