Making a hybrid quantum machine that would store quantum information in microscopic quantum objects with good coherence properties and that would process this information in a fast and efficient way with superconducting qubits is appealing. We report here an experiment along this idea, in which a macroscopic number of electronic spins is used as a single qubit memory, strongly coupled to a Josephson qubit by a quantum bus. The spins are nitrogen-vacancy centers in a diamond crystal, the qubit is a Cooper pair box of the Transmon type, and the bus a superconducting resonator with tunable frequency. We demonstrate strong coupling between the spins and the bus [1,2], vacuum Rabi oscillations between the qubit and the bus, as well as storage of a single photon from the qubit to the spins, and partial retrieval of it with fidelity of about 10%.
 Y. Kubo et al., Phys. Rev. Lett. 105, 140502 (2010).
 Y. Kubo et al., arxiv :quant-ph/1109.3860 (2011).