The possibility of implementing a cavity-enhanced off-resonant Raman quantum memory in an ensemble of silicon-vacancy centers in diamond is studied. It is shown that the signal-tonoise ratio at the output of the memory can significantly exceed unity for short single-photon pulses if the number of optical centers is small enough, which can be achieved with diamond samples in optical microresonators, and level splitting in their ground state is significantly enhanced by strain.

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Recently, the possibility of implementing a cavity-enhanced off-resonant Raman quantum memory in an ensemble of silicon-vacancy centers in diamond has been studied (Kalachev et al 2019 Laser Phys. 29 104001). It was shown that the signal-to-noise ratio can significantly exceed unity for short single-photon input pulses if the orbital level splitting in the ground state of the color centers is significantly enhanced by strain. The latter results in decreasing the coherence time between the two available orbital branches of the ground state, though. In the present work, we consider the possibility of increasing the storage time due to the use of nanodiamonds. It is shown that suppression of direct electron-phonon transitions in the diamond nanocrystals makes it possible to increase the coherence time of both orbital and spin qubits by orders of magnitude.

Abstract. The possibility of implementation of optical quantum memory via off-resonant Raman absorption and emission of single-photon pulses in rare-earth-ion-doped crystals is theoretically analysed taking into account signal-to-noise ratio at the output of the memory device. The crystal 143 Nd 3+ :Y 7 LiF4 is considered as an example. It is shown that the signal-tonoise ratio can exceed unity for single-photon input pulses provided that storage and retrieval of them is performed in the doped crystals forming a microcavity such as whispering gallery mode resonator.