Strong Coupling of a Spin Ensemble to a Superconducting Resonator

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Amongst all the microscopic quantum spin systems that can be coupled to superconducting circuits, negatively charged nitrogen- vacancy centers (N-V) in diamond are particularly attractive. One of the major reasons is that the spin coherence time has been shown to be as long as 2ms at room temperature. Compared to atoms, N-V centers are perfectly compatible with superconducting circuits, because they do not require challenging trapping techniques or large magnetic fields to bring them in resonance at GHz frequency with the circuit. This work that was a collaboration between the groups of Daniel Esteve (CEA) and Jörg Wrachtrup (USTUTT) reports the observation of a vacuum Rabi splitting in the transmission spectrum of superconducting resonator magnetically coupled to an ensemble of 1012 N-V centers with a very large collective coupling constant of 11 MHz. This demonstrates the strong coupling of a microscopic spin ensemble to a macroscopic circuit.

Y. Kubo, F. R. Ong, P. Bertet, D. Vion, V. Jacques, D. Zheng, A. Dréau, J.-F. Roch, A. Auffeves, F. Jelezko, J. Wrachtrup, M.F. Barthe, P. Bergonzo, D. Esteve
Phys. Rev. Lett. 105, 140502 (2010)