# Multi-pass configuration for Improved Squeezed Vacuum Generation in Hot Rb Vapor

## TL;DR

This paper demonstrates that multi-pass interaction with hot Rb vapor enhances squeezed vacuum generation by reducing mode contamination, achieving up to -2.6 dB of squeezing, and highlights the importance of spatial modes and cell configuration.

## Contribution

It introduces a multi-pass configuration that improves squeezing in hot Rb vapor, surpassing single-pass setups by optimizing interaction parameters.

## Key findings

- Multi-pass interaction increases squeezing by 0.6 dB.
- Spatial mode structure affects squeezing levels.
- Optical depth and cell configuration influence squeezing.

## Abstract

We study a squeezed vacuum field generated in hot Rb vapor via the polarization self-rotation effect. Our previous experiments showed that the amount of observed squeezing may be limited by the contamination of the squeezed vacuum output with higher-order spatial modes, also generated inside the cell. Here, we demonstrate that the squeezing can be improved by making the light interact several times with a less dense atomic ensemble. With optimization of some parameters we can achieve up to -2.6 dB of squeezing in the multi-pass case, which is 0.6 dB improvement compared to the single-pass experimental configuration. Our results show that other than the optical depth of the medium, the spatial mode structure and cell configuration also affect the squeezing level.