Realizing highly entangled states in asymmetrically coupled three NV
  centers at room temperature
Despite numerous efforts the coupling between randomly arranged multi-NV
centers and also resonators has not been improved significantly mainly due to
our limited knowledge of their entanglement times (2t_ent). Here, we
demonstrate a very strong coupling between three-NV centers by using a
simulated triple electron-electron resonance experiment based on a new quantum
(U_C) gate on IBM quantum simulator with 2t_ent ~12.5 microsecond arranged is a
triangular configuration. Interestingly through breaking the symmetry of
couplings an even lower 2t_ent ~6.3 {\mu}s can be achieved. This simulation not
only explains the luminescence spectra in recently observed three-NV centers
[Haruyama, Nat. Commun. 2019] but also shows a large improvement of the
entanglement in artificially created structures through a cyclic redistribution
of couplings. Realistically disordered coupling configurations of NV centers
qubits with short time periods and high (0.89-0.99) fidelity of states clearly
demonstrate possibility of accurate quantum registers operated at room
temperature.
Declan Mahony Somnath Bhattacharyya