Storage of a single photon in a room temperature vapor cell for a second

量子网络和量子密钥分发通过利用单光子的量子性质来提供安全通信。量子中继器或纠缠蒸馏需要量子存储器，以便真正创建可扩展性和长距离信息传输。在光量子信息处理中，量子存储器有助于延迟和同步光子量子比特。一般来说，量子存储器必须一致地存储和释放光子，并且应该与光学微集成兼容，以允许未来的可扩展性。对于这个建议，我们选择了有前途的平台，室温碱性气体电池。利用电磁感应透明（EIT）技术，单光子以自旋相干的形式存储在铯原子的超精细态中。我们将展示在这种存储器中尚未同时实现的三个关键特性：（1）长相干时间，（2）在大背景下存储后有效提取单光子信号，以及（3）大存储带宽。基于Katz和Firstenberg的建议，我们将利用低磁场下Δm = 1的两个超精细态之间的塞曼相干性来开发一个无自旋交换弛豫（SERF）子空间。作为他们协议的修改，我们将使用能量分裂的F=3和F=4超精细基态，以便使用专门的滤波器系统对存储的信号进行光谱滤波。足够大的带宽将通过足够高的EIT耦合激光器的功率来实现。我们的目标是在量子光存储方面取得突破性的结果，即，在室温下，在碱性气体蒸气室中，以100 MHz带宽存储和检索单个光子超过1秒。真正的单光子将从两个源存储和产生：一个是基于腔增强自发参量下转换的预示源，另一个是使用半导体量子点的按需源。两个源将匹配到存储器的Cs D1线。

Quantum networks and quantum key distribution provide secure communication by exploiting the quantum nature of single photons. Quantum memories are required for quantum repeaters or entanglement distillation in order to truly create scalability and long-distance information transfer. In optical quantum information processing, quantum memories help to delay and synchronize the photonic qubits. In general, quantum memories must store and release photons coherently and should be compatible with optical micro-integration to allow for future scalability. For this proposal we chose the promising platform of room temperature alkali gas cells. With electromagnetically induced transparency (EIT) single photons are stored as spin coherence in hyperfine states of cesium. We will demonstrate three key properties, which have not been realized at the same time in this kind of memories: (1) long coherence times, (2) efficient extraction of a single-photon signal after storage against a large background, and (3) large storage bandwidth. Building on a proposal by Katz & Firstenberg, we will exploit a Spin-Exchange Relaxation-Free (SERF) subspace by utilizing Zeeman coherence between two hyperfine states with Δm = 1 at low magnetic fields. As a modification of their protocol, we will use the energetically split F=3 and F=4 hyperfine ground state in order to implement spectral filtering of the stored signal using a specialized filter system. A large enough bandwidth will be achieved by sufficiently high power of the EIT coupling laser.We aim for a breakthrough result concerning the storage of quantum light, i.e., the storage and retrieval of a single photon with 100 MHz bandwidth for a time exceeding one second in an alkali gas vapor cell at room temperature. True single photons will be stored and generated from two sources: one is a heralded source based on cavity-enhanced spontaneous parametric down conversion, the other is an on-demand source using semiconductor quantum dots. Both sources will be matched to the Cs D1 line of the memory.