Curator's Take
AI Commentary
This article demonstrates the first non‑classical storage of telecom‑heralded single photons in a rare‑earth crystal using an AFC spin‑wave memory combined with an XY4 microwave rephasing sequence, extending quantum‑compatible storage to 180 µs and classical echoes up to ~3 ms. By marrying long‑lived hyperfine coherence with a telecom‑band photon source, the work bridges two critical hurdles for quantum repeaters—low‑loss transmission and on‑demand retrieval of entangled photons. While efficiencies and multiplexing still need scaling, the result marks a concrete step toward practical, long‑distance quantum networks.
— Mark Eatherly
Summary
Long-lived storage of single photons under the form of atomic excitations is at the foundation of long-distance entanglement distribution in quantum networks. To mitigate decoherence effects induced by the environment, rephasing of the hyperfine coherences using microwave pulses have been implemented in a variety of single-emitter and ensemble-based solid-state systems. However, the demonstration of storage of single photons in an absorptive quantum memory including such spin rephasing mechanism remains elusive. In this work, we show non-classical storage of telecom-heralded single photons in a Pr$^{3+}$:Y$_2$SiO$_5$ rare-earth ion doped crystal quantum memory using the atomic frequency comb (AFC) spin-wave protocol combined with a XY4 spin rephasing sequence. Long-lived AFC photon echoes are first observed in the classical regime for storage times of up to approximately 3 ms. We then demonstrate non-classical correlations between heralding photons and stored signal photons generated by a cavity-enhanced parametric photon-pair source for storage times of up to 180 $μ$s and with measured cross-correlation values as high as 4.6(4). Together with the capacity of Pr$^{3+}$:Y$_2$SiO$_5$ QMs to support highly efficient and multiplexed storage, this result represents a significant step towards scalable long-distance quantum repeater links.