Two-mode squeezing of distant nitrogen-vacancy-center ensembles by manipulating the reservoir

We present a scheme to engineer a two-mode squeezed state of effective bosonic modes realized by collective excitations of two distant nitrogen-vacancy-center ensembles (NVEs) coupled to separated transmission line resonators (TLRs), which are interconnected by a current-biased Josephson-junction superconducting qubit. By making use of the engineered NVE-TLR magnetic coupling with Raman transition between the ground sublevels of the NVEs, we may manipulate the artificial reservoir by tuning the external driving fields. The TLR decay induces an artificial reservoir, which can drive the system to the desired entangled squeezed states. Our idea provides a scalable way to a NVE-based continuous-variable quantum-information processing, which is close to being achievable with currently available technology.