Polarization squeezing at the audio frequency band for the Rubidium D1 line

TL;DR

This paper reports a 2.8-dB polarization squeezing of the Stokes operator at the rubidium D1 line, achieved at audio frequencies, with improved methods to enhance low-frequency squeezing for quantum sensing applications.

Contribution

It introduces two methods to improve low-frequency polarization squeezing and demonstrates squeezing at the rubidium D1 line for quantum magnetometry.

Findings

Achieved 2.8-dB polarization squeezing at 2.6 kHz

Implemented orthogonal-polarized locking and quantum noise locking methods

Squeezing limited by absorption-induced losses at 397.5 nm

Abstract

A 2.8-dB polarization squeezing of the Stokes operator S2 for the rubidium D1 line (795 nm) is achieved, with the lowest squeezing band at an audio frequency of 2.6 kHz. Two methods are applied for improving the squeezing towards low frequencies: an orthogonal-polarized locking beam that precludes residual unwanted interference and quantum noise locking method that stabilizes the relative phase between the squeezed vacuum and the local oscillator. The squeezing level is limited by absorption-induced losses at short wavelengths, here is 397.5 nm. The generated polarization squeezed light can be used in a quantum enhanced magnetometer to increase the measurement sensitivity.