Two-photon quantum gates with a single V-type atom

We show that a single three-level atom in the V configuration can potentially perform an ideal CPHASE gate between two photons, each described by a single mode field, by controlling the interaction time (and, optionally the detuning). The single-mode description would require the operation to take place in a high-finesse cavity in the strong-coupling limit. Getting the field in and out of the cavity while avoiding wavepacket distortion might be accomplished using dynamical coupling techniques, in which case the principal limitation would be the atom's spontaneous emission rate out of the cavity mode.