# Microwave to optical conversion with atoms on a superconducting chip

## TL;DR

This paper proposes a scheme for coherent microwave-to-optical photon conversion using a cold atomic ensemble on a superconducting chip, enabling efficient transfer without strong optical cavity coupling.

## Contribution

It introduces a novel free-space conversion method utilizing Rydberg atoms on a superconducting chip, avoiding the need for resonant optical cavities.

## Key findings

- High conversion efficiency with few thousand atoms
- Photon emitted into a well-defined mode
- Operates without strong optical cavity coupling

## Abstract

We describe a scheme to coherently convert a microwave photon of a superconducting co-planar waveguide resonator to an optical photon emitted into a well-defined temporal and spatial mode. The conversion is realized by a cold atomic ensemble trapped above the surface of the superconducting atom chip, near the antinode of the microwave cavity. The microwave photon couples to a strong Rydberg transition of the atoms that are also driven by a pair of laser fields with appropriate frequencies and wavevectors for an efficient wave-mixing process. With only few thousand atoms in an ensemble of moderate density, the microwave photon can be completely converted into an optical photon emitted with high probability into the phase matched direction and, e.g., fed into a fiber waveguide. This scheme operates in a free-space configuration, without requiring strong coupling of the atoms to a resonant optical cavity.