Phonon induced pure dephasing in color centers from first principles*

Understanding dephasing mechanisms is the key to improving the performance of color centers for quantum information science applications. Phonon-induced processes, being intrinsic, cannot be removed by improving sample quality, and must be considered for all color centers. In this talk, we consider phonon-induced pure dephasing associated with the fluctuation of spin levels. Unlike the energy relaxation contribution, the pure dephasing contribution does not involve energy transfer. We compute these dephasing rates from density functional theory for nitrogen vacancy centers in diamond, obtaining good agreement with experiments, and showing that phonon-induced pure dephasing is a limiting contribution for clean samples at low temperatures.  The largest contributions to the dephasing is attributed local phonon modes and local-continuum resonances associated with movement of the nearest- and second-nearest carbon neighbors of the vacancy.