Controllable-dipole quantum memory

Abstract

We present a quantum memory protocol for photons that is based on the direct control of the transition dipole moment. We focus on the case where the light-matter interaction is enhanced by a cavity. We show that the optimal write process (maximizing the storage efficiency) is related to the optimal read process by a reversal of the effective time $\ensuremath{\tau}=\ensuremath{\int}dt\phantom{\rule{0.16em}{0ex}}{g}^{2}(t)/\ensuremath{\kappa}$, where $g(t)$ is the time-dependent coupling and $\ensuremath{\kappa}$ is the cavity decay rate. We discuss the implementation of the protocol in a rare-earth-ion--doped crystal where an optical transition can be turned on and off by switching a magnetic field.