A quantum memory at microwave frequencies, able to store the state of multiple superconducting qubits over long times, is a desirable device in many quantum information protocols. Spins in crystals are ideally suited for implementing this idea, because of their long coherence times, and of their intrinsic multi-mode character. I will discuss our efforts towards the implementation of a spin-ensemble based quantum memory, using NV centers in diamond. First I will describe the quantum memory protocol that we have proposed . I will then show that it is indeed possible to store a superconducting qubit state in a collective state of approximately 1011 NV centers . I will finally describe our efforts to implement spin-echo-type pulse sequences that should enable us to extend the storage time of the NV ensemble by orders of magnitude .
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