Quantum Storage of Photonic Entanglement in a Crystal

TL;DR

This paper demonstrates the first entanglement storage of a photon in a crystal, showing potential for solid-state quantum communication and repeaters by preserving entanglement over time.

Contribution

It reports the first successful storage and retrieval of photonic entanglement in a crystal, advancing solid-state quantum memory technology.

Findings

Entanglement stored and retrieved in a crystal with high fidelity.

Violation of CHSH inequality confirms preserved entanglement.

Paves the way for solid-state quantum repeaters.

Abstract

Entanglement is the fundamental characteristic of quantum physics. Large experimental efforts are devoted to harness entanglement between various physical systems. In particular, entanglement between light and material systems is interesting due to their prospective roles as "flying" and stationary qubits in future quantum information technologies, such as quantum repeaters and quantum networks. Here we report the first demonstration of entanglement between a photon at telecommunication wavelength and a single collective atomic excitation stored in a crystal. One photon from an energy-time entangled pair is mapped onto a crystal and then released into a well-defined spatial mode after a predetermined storage time. The other photon is at telecommunication wavelength and is sent directly through a 50 m fiber link to an analyzer. Successful transfer of entanglement to the crystal and back is proven by a violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality by almost three standard deviations (S=2.64+/-0.23). These results represent an important step towards quantum communication technologies based on solid-state devices. In particular, our resources pave the way for building efficient multiplexed quantum repeaters for long-distance quantum networks.