Long-lived dark states in a superconductor diamond hybrid quantum system

The research into quantum science and technology has reached an interesting stage where we can now in principle engineer composite systems to exploit the best properties of these individual systems. Such hybridization techniques have been demonstrated for instance with superconducting circuits and electron spin ensembles where strong coupling and the coherent transfer & storage of quantum information has been achieved. However in these cases, generally the hybrid system properties have not exceeded those of the individual systems. Recently we have observed a remarkably sharp resonance in the spectrum of flux qubit NV- diamond hybrid quantum system with no external magnetic field applied to the diamond. What is surprising is that its measured line-width is much narrower than that of both the flux-qubit and spin ensemble. We show this resonance is evidence of a collective & long-lived dark state.