title: Conditional-phase switch at the single-photon level.
abstract: We present an experimental realization of a two-photon conditional phase switch, related to the " c-phis;" gate of quantum computation. This gate relies on quantum interference between photon pairs and generates entanglement between two optical modes through the process of spontaneous parametric down-conversion (SPDC). The interference effect serves to enhance the effective nonlinearity by many orders of magnitude, so it is significant at the quantum (single-photon) level. By adjusting the relative optical phase between the classical pump for SPDC and the pair of input modes, one can impress a large phase shift on one beam which depends on the presence or absence of a single photon in a control mode.
authors.affiliation: Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Resch
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Lundeen
authors.forename: Aephraim M
authors.initials: AM
authors.lastname: Steinberg