The generation and distribution of entanglement are key resources in quantum repeater schemes. Temporally multiplexed systems offer time-bin encoding of quantum information which provides robustness against decoherence in fibers, crucial in long distance communication. Here we demonstrate the direct generation of entanglement in time between a photon and a collective spin excitation in a rare earth ion doped ensemble. We analyze the entanglement by mapping the atomic excitation onto a photonic qubit and by using time-bin qubits analyzers implemented with another doped crystal using the atomic frequency comb technique. Our results provide a solid-state source of entangled photons with embedded quantum memory. Moreover, the quality of the entanglement is high enough to enable a violation of a Bell inequality by more than two standard deviations.
@article{arxiv.1904.02537,
title = {Time Entanglement between a Photon and a Spin Wave in a Multimode Solid-state Quantum Memory},
author = {Kutlu Kutluer and Emanuele Distante and Bernardo Casabone and Stefano Duranti and Margherita Mazzera and Hugues de Riedmatten},
journal= {arXiv preprint arXiv:1904.02537},
year = {2019}
}