# Quantum interference between photons from an atomic ensemble and a remote atomic ion

## TL;DR

This paper demonstrates quantum interference between photons emitted from a single atomic ion and a neutral-atom ensemble across separate locations, advancing the development of hybrid quantum networks.

## Contribution

First demonstration of quantum interference between photons from a single ion and an atomic ensemble in different buildings linked by optical fiber.

## Key findings

- High-visibility interference observed between the two photon sources.
- Successful linking of disparate quantum systems over a fiber network.
- Progress towards establishing a hybrid quantum network.

## Abstract

Advances in the distribution of quantum information will likely require entanglement shared across a hybrid quantum network. Many entanglement protocols require the generation of indistinguishable photons between the various nodes of the network. This is challenging in a hybrid environment due to typically large differences in the spectral and temporal characteristics of single photons generated in different systems. Here we show, for the first time, quantum interference between photons generated from a single atomic ion and an atomic ensemble, located in different buildings and linked via optical fibre. Trapped ions are leading candidates for quantum computation and simulation with good matter-to-photon conversion. Rydberg excitations in neutral-atom ensembles show great promise as interfaces for the storage and manipulation of photonic qubits with excellent efficiencies. Our measurement of high-visibility interference between photons generated by these two, disparate systems is an important building block for the establishment of a hybrid quantum network.