# Entanglement between more than two hundred macroscopic atomic ensembles in a solid

## TL;DR

This paper demonstrates the creation and verification of entanglement among over two hundred macroscopic atomic ensembles within a solid, using a photon stored in a crystal and interference effects, marking a significant step in quantum entanglement research.

## Contribution

The authors experimentally establish entanglement among more than two hundred large atomic ensembles in a solid, a novel achievement in macroscopic quantum entanglement.

## Key findings

- Entanglement demonstrated among over 200 atomic ensembles.
- Lower bound for number of entangled ensembles derived from interference contrast.
- Each ensemble contains a billion atoms and exhibits further entanglement.

## Abstract

We create a multi-partite entangled state by storing a single photon in a crystal that contains many large atomic ensembles with distinct resonance frequencies. The photon is re-emitted at a well-defined time due to an interference effect analogous to multi-slit diffraction. We derive a lower bound for the number of entangled ensembles based on the contrast of the interference and the single-photon character of the input, and we experimentally demonstrate entanglement between over two hundred ensembles, each containing a billion atoms. In addition, we illustrate the fact that each individual ensemble contains further entanglement. Our results are the first demonstration of entanglement between many macroscopic systems in a solid and open the door to creating even more complex entangled states.