Large cross-phase modulation between slow co-propagating weak pulses in 87Rb

Strong optical cross-phase modulation (XPM) for weak fields is tremendously important, e.g. for optical quantum information processing and for all-optical switches in classical communication. Proposals based on electromagnetically induced transparency (EIT) have been brought forward, XPM is experimentally challenging. One problem is to achieve equal slow group velocities (double EIT) to maximize the interaction time. We present a scheme that exploits the best features of previous proposals and adds new techniques, thereby optimizing XPM. We propose a preparational procedure for the atomic initial state that enables double EIT with a single atomic species and present an implementation of the scheme for 87Rb with a single pump laser and a magnetic field. Furthermore, we study the nonlinear evolution of the two weak signal pulses and present a new upper bound on the maximal XPM phase shift achievable for two single-photon pulses.\\r\\n \\r\\n* This work is being supported by iCore, Alberta\\r\\n