Thermal preparation of an entangled steady state of spin ensembles

Steady state entanglement is studied in the continuous-variable system of two distant ensembles of electronic spins driven by squeezed microwave field. Proposed circuit consists of two distant nitrogen-vacancy-center ensembles coupled to transmission line resonator. Squeezed microwave field is generated by a flux-driven Josephson parametric amplifier. The time evolution of the system is described by the master equation for density operator. Criterion based on logarithmic negativity is used for the detection of entanglement. Squeezed field of the Josephson parametric amplifier is driving force, which provides steady state entanglement between two bosonic modes of nitrogen-vacancy-center ensembles for a wide range of system parameters. This can open the way for implementation of continuous-variable states for quantum computing applications.