Ensemble‐Based Quantum Memory: Principle, Advance, and Application

Quantum memory for photons plays an important role in quantum information science, such as quantum repeater, quantum network, quantum communication, and quantum computing. The realization of a quantum memory with high efficiency, long lifetime, high fidelity, large bandwidth, and multimode capacity is of great significance for its applications. Atomic ensemble, serving as one of the most appealing physical platforms for quantum memories, has been widely explored toward improving memory performance. Over the past decades, significant progress based on atomic ensembles has been made in developing new schemes and improving memory performances experimentally through various approaches. In this chapter, we first introduce the working principle of quantum memory by reviewing the widely used schemes. Next, we present several key figures of merit for judging memory performance. Afterward, we review the experimental progress made in several different systems. Finally, we give discussions on its application in a number of different directions. The scope of this chapter is limited to single-photon storage with atomic ensembles.