A cavity-mediated quantum CPHASE gate between NV spin qubits in diamond

Abstract

While long spin coherence times and efficient single-qubit quantum control have been implemented successfully in nitrogen-vacancy (NV) centers in diamond, the controlled coupling of remote NV spin qubits remains challenging. Here, we propose and analyze a controlled-phase (CPHASE) gate for the spins of two NV centers embedded in a common optical cavity and driven by two off-resonant lasers. In combination with previously demonstrated single-qubit gates, CPHASE allows for arbitrary quantum computations. The coupling of the NV spin to the cavity mode is based upon Raman transitions via the NV excited states and can be controlled with the laser intensities and relative phase. We find characteristic laser frequencies at which a laser photon is only scattered into the cavity mode if the NV center spin is |ms=0⟩, and not in the case |ms=-1⟩, or vice versa. The scattered photon can be reabsorbed by another selectively driven NV center and generate a conditional phase (CPHASE) gate. Gate times below 20 ns are within reach, several orders of magnitude shorter than typical NV spin coherence times. The separation between the two NV centers is only limited by the extension of the cavity.