Nonlocal entanglement concentration of separate nitrogen-vacancy centers coupling to microtoroidal resonators

Here we propose two practical protocols to concentrate entanglement between separate nitrogen-vacancy (N-V) centers in less entangled state via coupling to microtoroidal resonators. We construct the parity check gate of the N-V center and microtoroidal resonator systems via the interaction with the ancillary photon input-output process near the microtoroidal resonators. Thus the parity of the N-V center state can be readout by the measurement on the ancillary photon. Then we introduce the parity check operations to entanglement concentration protocols. Considering current techniques, we also discuss the feasibility of our proposal and its experimental challenges.

The Advantages of Not Entangling Macroscopic Diamonds at Room Temperature

The recent paper entitled by K. C. Lee et al. (2011) establishes nonlocal macroscopic quantum correlations, which they term “entanglement”, under ambient conditions. Photon(s)-phonon entanglements are established within each interferometer arm. However, our analysis demonstrates, the phonon fields between arms become correlated as a result of single-photon wavepacket path indistinguishability, not true nonlocal entanglement. We also note that a coherence expansion (as opposed to decoherence) resulted from local entanglement which was not recognized. It occurred from nearly identical Raman scattering in each arm (importantly not meeting the Born and Markovian approximations). The ability to establish nonlocal macroscopic quantum correlations through path indistinguishability rather than entanglement offers the opportunity to greatly expand quantum macroscopic theory and application, even though it was not true nonlocal entanglement.