Abstract: Via atomic cascade emission, an entangled pair of photons may be generated. A first one of the entangled pair may be ideal for long-distance communication. The other one may be suited for mapping to a long-lived atomic memory. Also, a deterministic single photon may be produced using a feedback system. If the feedback system indicates that an excitation exists in an atomic ensemble, then the atomic ensemble may be hit with a laser to produce the deterministic single photon. Furthermore, gas in the atomic ensemble may be subdivided into independent elements each of which may function as a memory element itself. In addition, dual species matter qubits may be entangled with light. A volume in an atomic ensemble may comprise a first isotope vapor storing a first state of a qubit. The volume may also comprise a second isotope vapor configured to store a second state of the qubit.

Abstract: Disclosed are apparatus and methods that provide for a coherent quantum state transfer of information from a two-level atomic system (matter) to a single photon (light). Entanglement between a single photon (signal) and a two-component atomic ensemble of cold Rubidium atoms is used to project a quantum memory element (the atomic ensemble) onto any desired state by measuring the signal in a suitable basis. The atomic qubit is read out by stimulating directional emission of a single photon (idler) from the (entangled) collective state of the ensemble. Faithful atomic memory preparation and readout are verified by observed correlations between the signal and idler photons. These results are an important component of distributed quantum networking.