Controllable Coupling between Flux Qubit and Nanomechanical Resonator*

We propose an active mechanism for coupling the quantized mode of a nanomechanical resonator to the persistent current in the loop of superconducting flux qubit. This coupling is independently controlled by an external coupling magnetic field. The whole system forms a novel solid-state cavity QED architecture in strong coupling limit which has broad applications in demonstrating quantum optical phenomena in solid state system and solid-state quantum computing. The coupling mechanism is applicable for more generalized situations where the superconducting Josephson junction system acts as a multi-level quantum system. We also address the practical issues concerning experimental realization.