Entanglement between a telecom photon and an on-demand multimode solid-state quantum memory

TL;DR

This paper demonstrates entanglement between a telecom photon and a multimode solid-state quantum memory, showcasing on-demand storage and potential for long-distance quantum communication.

Contribution

First demonstration of telecom photon entanglement with a multimode solid-state quantum memory using atomic frequency comb scheme.

Findings

Achieved conditional fidelities of 92% and 77% for different storage methods.

Extended entanglement storage up to 47.7 microseconds.

Potential for entanglement distribution over 10 km distances.

Abstract

Entanglement between photons at telecommunication wavelengths and long-lived quantum memories is one of the fundamental requirements of long-distance quantum communication. Quantum memories featuring on-demand read-out and multimode operation are additional precious assets that will benefit the communication rate. In this work we report the first demonstration of entanglement between a telecom photon and a collective spin excitation in a multimode solid-state quantum memory. Photon pairs are generated through widely non-degenerate parametric down-conversion, featuring energy-time entanglement between the telecom-wavelength idler and a visible signal photon. The latter is stored in a Pr$^{3+}$:Y$_2$SiO$_5$ crystal as a spin wave using the full Atomic Frequency Comb scheme. We then recall the stored signal photon and analyze the entanglement using the Franson scheme. We measure conditional fidelities of $92(2)\%$ for excited-state storage, enough to violate a CHSH inequality, and $77(2)\%$ for spin-wave storage. Taking advantage of the on-demand read-out from the spin state, we extend the entanglement storage in the quantum memory for up to 47.7~$\mu$s, which could allow for the distribution of entanglement between quantum nodes separated by distances of up to 10 km.