Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali-vapor Raman memories combine high-bandwidth storage, on-demand readout, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and have suffered from four-wave-mixing noise. Here, we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering antiresonance for the anti-Stokes field, we also suppress the four-wave-mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapor memory, (15±2)×10−3 photons per pulse, with a total efficiency of (9.5±0.5)%.
Saunders, D. J., Munns, J. H. D., Champion, T. F. M., Qiu, C., Kaczmarek, K. T., Poem, E., Ledingham, P. M., Walmsley, I. A., & Nunn, J. (2016). Cavity-enhanced room-temperature broadband Raman memory. Physical Review Letters, 116(9), 1-5. . https://doi.org/10.1103/PhysRevLett.116.090501