# Entanglement-preserving frequency conversion in cold atoms

## TL;DR

This paper introduces a method for efficient, lossless quantum frequency conversion in cold atoms that preserves quantum coherence and entanglement, enabling advanced quantum communication applications.

## Contribution

The paper presents a novel scheme for entanglement-preserving frequency conversion using strong parametric coupling in slow-light atomic media.

## Key findings

- Efficient, shape-conserving frequency conversion demonstrated.
- Quantum coherence and entanglement are maintained during conversion.
- Potential for generating narrow-band entangled photon states.

## Abstract

We propose a method that enables efficient frequency conversion of quantum information based on recently demonstrated strong parametric coupling between two single-photon pulses propagating in a slow-light atomic medium at different group velocities. We show that an incoming single-photon state is efficiently converted into another optical mode in a lossless and shape-conserving manner. The persistence of initial quantum coherence and entanglement within frequency conversion is also demonstrated. We first illustrate this result for the case of small frequency difference of converted photons, and then discuss the modified scheme for conversion of photon wavelengths in different spectral ranges. Finally we analyze the generation of a narrow-band single-photon frequency-entangled state.