Optical spin-wave memory with storage efficiency significantly enhanced by an optical cavity was reported in a submission to the New Journal of Physics . Although the cavity has low finesse, it is operated under impedance matching conditions to achieve high absorption in a spectral-hole burning crystal that is intrinsically low absorbing. The experiments utilized Eu3+:Y2SiO5 cooled to 3 Kelvin, and produced a 12-fold increase in storage efficiency. The results reveal a promising approach to improve the state-of-the-art in storing optical pulses at the single-photon level. The Montana Instruments Cryostation used in these experiments was contained within the optical cavity as shown in the right panel of Fig. 1.
Fig. 1. Experimental set-up showing the laser source with frequency stabilization (left), the beam is split into storage and control modes (center), and the storage or memory (right) where the crystal resides. The memory segment includes the Cryostation, optical cavity with its two mirrors. A piezo element on one mirror is used to maintain resonance.
 P. Jobez, I. Usmani, N. Timoney, C. Laplane, N. Gisin, and M. Afzelius, arXiv:1404.3489v1.
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