  We present a thorough derivation of the excited state energy levels of the
negatively charged $^{15}$N-V$^{-}$ center in diamond for the strong applied
electric field case. We show that in the $^{15}$N-V$^{-}$ center a spin
non-conserving two-photon $\Lambda$ transition exists that is mediated by the
hyperfine interaction, which provides the possibility to write quantum
information. Using second order perturbation theory we obtain a $\Lambda$
transition rate of the order of 10 MHz at room temperature, which allows for
approximately $10^4$ quantum logic operations within the spin coherence time
$\tau_d(T=300 K)\approx 1m$s of the $^{15}$N-V$^{-}$ center.
