T. J. Watson Laboratory of Applied Physics, California Institute of Technology, 1200 E California Boulevard, Pasadena, California 91125, USA.
Nat Commun. 2017 Jan 16;8:14107. doi: 10.1038/ncomms14107.
Ensembles of solid-state optical emitters enable broadband quantum storage and transduction of photonic qubits, with applications in high-rate quantum networks for secure communications and interconnecting future quantum computers. To transfer quantum states using ensembles, rephasing techniques are used to mitigate fast decoherence resulting from inhomogeneous broadening, but these techniques generally limit the bandwidth, efficiency and active times of the quantum interface. Here, we use a dense ensemble of neodymium rare-earth ions strongly coupled to a nanophotonic resonator to demonstrate a significant cavity protection effect at the single-photon level-a technique to suppress ensemble decoherence due to inhomogeneous broadening. The protected Rabi oscillations between the cavity field and the atomic super-radiant state enable ultra-fast transfer of photonic frequency qubits to the ions (∼50 GHz bandwidth) followed by retrieval with 98.7% fidelity. With the prospect of coupling to other long-lived rare-earth spin states, this technique opens the possibilities for broadband, always-ready quantum memories and fast optical-to-microwave transducers.
固态光学发射器的集合体实现了光子量子比特的宽带量子存储和转换，在用于安全通信和连接未来量子计算机的高速率量子网络中有应用。为了使用集合体来传输量子态，重相位技术被用来减轻由于不均匀展宽导致的快速退相干，但这些技术通常会限制量子接口的带宽、效率和活动时间。在这里，我们使用强耦合到纳米光子谐振器的密集的钕稀土离子集合体，在单光子水平上展示了显著的腔保护效应——一种抑制由于不均匀展宽导致的集合体退相干的技术。腔场和原子超辐射态之间的受保护的拉比振荡使得光子频率量子比特能够以超快的速度（~50GHz 带宽）转移到离子中，然后以 98.7%的保真度进行检索。有了与其他长寿命稀土自旋态耦合的前景，这项技术为宽带、随时可用的量子存储器和快速光到微波转换器开辟了可能性。
