Progress towards a quantum memory with telecom-frequency conversion

Abstract

Quantum networks provide conduits capable of transmitting quantum information that connect to nodes at remote locations where the quantum information can be stored or processed. Fiber-based transmission of quantum information over long distances may be achieved using quantum memory elements and quantum repeater protocols. However, atombased quantum memories typically involve interactions with light fields outside the telecom window needed to minimize absorption in transmission by optical fibers. We report on progress towards a quantum memory based on the generation of 795 nm spontaneously emitted single photons by a write-laser beam interacting with a cold ⁸⁷Rb ensemble. The single photons are then frequency-converted into (out of) the telecomm band via difference (sum) frequency generation in a PPLN crystal. Finally, the atomic state is read out via the interaction of a read-pulse with the quantum memory. With such a system, it will be possible to realize a long-lived quantum memory that will allow transmission of quantum information over many kilometers with high fidelity, essential for a scalable, long-distance quantum network.