# Quantum properties of light propagating in a Coherent Population Oscillation Storage Medium

## TL;DR

This paper investigates the quantum properties of light in a Coherent Population Oscillation medium, showing that quantum noise degrades during propagation, limiting quantum storage capabilities.

## Contribution

It provides experimental and theoretical analysis of quantum field propagation in CPO media, revealing limitations for quantum state storage due to spontaneous emission effects.

## Key findings

- Quantum noise degrades during propagation in CPO media
- Spontaneous emission destroys quantum noise properties
- Quantum states tend to become coherent states after propagation

## Abstract

We study the propagation and storage of a quantum field using ultra-narrow Coherent Population Oscillations (CPO) in a $\Lambda-$type atomic medium. The predictions for classical fields are checked experimentally in a metastable vapor at room temperature. We derive the evolution of its squeezing spectrum in the presence of a large classical pump field which enables CPO to exist. We show that the spontaneous emission of the residual population pumped into the excited state progressively destroys the quantum noise properties of the quantum field along propagation. The output quantum field therefore tends to be a coherent state, discarding the possibility to store quantum states of light with CPO.