  Nitrogen-vacancy (NV) defect centers in diamond are strong candidates to
generate entangled states in solid-state environments even at room temperature.
Quantum correlations in spatially separated NV systems, for distances between
NVs ranging from a few nanometers to a few kilometers, have been recently
reported. In the present work we consider the entanglement transfer from two-
mode microwave squeezed (entangled) photons, which are in resonance with the
two lowest NV electron spin states, to initially unentangled NV centers. We
first demonstrate that the entanglement transfer process from quantum
microwaves to isolated NV electron spins is feasible. We then proceed to extend
the previous results to more realistic scenarios where 13 C nuclear spin baths
surrounding each NV are included, quantifying the entanglement transfer
efficiency and robustness under the effects of dephasing/dissipation noisy
nuclear baths. Finally, we address the issue of assessing the possibility of
entanglement transfer from the squeezed microwave light to two remote nuclear
spins closely linked to different NV centers.
