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

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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.