Conditional sign flip of two photons without pulse distortion

Abstract

We theoretically demonstrate a deterministic conditional sign flip of a two-photon pulse that preserves the pulse profile. The nonlinear optical system used is a $V$-type three-level atom confined in a cavity, and the input photons are down-converted twin photons having temporal entanglement. The input and the output pulse profiles are nearly perfectly preserved when the reciprocal bandwidth of the input photons is tuned to the atomic linewidth.