Improved Light-Matter Interaction in a Thulium Cavity Memory for Quantum Light Storage

We design and implement an atomic frequency comb quantum memory using a thulium-doped crystal in an impedance matched optical cavity to create absorption of more than 90% of input signal, resulting in a memory efficiency of 27%. This low finesse optical cavity design enables efficient storage over the conventionally large frequency bandwidths ( ≥ 500 MHz) present for single photons and high communication rates. We store one member of a photon pair created through spontaneous parametric down-conversion and, by measuring a value of g(2)=9.3 ± 1.2 > 2 for the cross-correlation function of the photons, verify that the non-classical nature of the light persists after storage in the cavity memory. Using quantum process tomography to measure time-bin qubits after storage in this high-bandwidth memory, we characterize the qubit storage fidelity to be as high as F = 95.0 ± 0.1%, confirming non-classical qubit storage. These results demonstrate progress toward efficient, faithful, and high bandwidth storage of single photon qubits for quantum networking.