title: Nonlinear optics with less than one photon.
abstract: We demonstrate suppression and enhancement of spontaneous parametric down-conversion via quantum interference with two weak fields from a local oscillator (LO). Effectively, pairs of LO photons up-convert with high efficiency for appropriate phase settings, exhibiting an effective nonlinearity enhanced by at least 10 orders of magnitude. This constitutes a two-photon switch and promises to be applicable to a wide variety of quantum nonlinear optical phenomena.
authors.affiliation: Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7.
authors.forename: K J
authors.initials: KJ
authors.lastname: Resch
authors.forename: J S
authors.initials: JS
authors.lastname: Lundeen
authors.forename: A M
authors.initials: AM
authors.lastname: Steinberg