Principal Investigator Jeffrey Shapiro
Co-investigator Franco Wong
The architecture for long-distance quantum communication relies on fiber-optic transmission of polarization-entangled photons from a dual parametric amplifier source to a pair of trapped Rb atom quantum memories. The protocol requires a high-flux continuous-wave source of polarization-entangled photons at 795 nm and 1.55 mm, for the loading of local and remote quantum memories, respectively. Out of each pair of entangled photons produced by the source, one of the photons is sent to Alice's local station while the conjugate photon travels over standard telecommunication fiber to Bob's remote receiver node. In order to load the remotely-located memory, quantum-state frequency conversion is required, so that the polarization state of the 1.55 mm photon is transferred to a 795 nm photon. This form of frequency upconversion must function down to the single photon level with low insertion loss, while providing both high conversion efficiency and high-fidelity preservation of arbitrary polarization states. We have demonstrated 90%-efficient single-photon frequency upconversion for a single polarization, using a bulk periodically-poled lithium niobate (PPLN) crystal embedded in a pump enhancement ring cavity. We have also demonstrated 50%-efficient polarization-preserving upconversion in a novel bidirectional PPLN upconverter whose performance was pump power limited.