Storage and retrieval of microwave fields at the single-photon level in a spin ensemble

C. Grezes, B. Julsgaard, Y. Kubo, W. L. Ma, M. Stern, A. Bienfait, K. Nakamura, J. Isoya, S. Onoda, T. Ohshima, V. Jacques, D. Vion, D. Esteve, R. B. Liu, K. Mølmer, P. Bertet

Published 2015-04-09Version 1

We report the storage of microwave pulses at the single-photon level in a spin-ensemble memory consisting of $10^{10}$ NV centers in a diamond crystal coupled to a superconducting LC resonator. The energy of the signal, retrieved $100\, \mu \mathrm{s}$ later by spin-echo techniques, reaches $0.3\%$ of the energy absorbed by the spins, and this storage efficiency is quantitatively accounted for by simulations. This figure of merit is sufficient to envision first implementations of a quantum memory for superconducting qubits.