A single-photon transistor using nanoscale surface plasmons

Photons rarely interact-which makes it challenging to build all-optical devices in which one light signal controls another. Even in nonlinear optical media, in which two beams can interact because of their influence on the medium's refractive index, this interaction is weak at low light levels. Here, we propose a novel approach to realizing strong nonlinear interactions at the single-photon level, by exploiting the strong coupling between individual optical emitters and propagating surface plasmons confined to a conducting nanowire. We show that this system can act as a nonlinear two-photon switch for incident photons propagating along the nanowire, which can be coherently controlled using conventional quantum-optical techniques. Furthermore, we discuss how the interaction can be tailored to create a single-photon transistor, where the presence (or absence) of a single incident photon in a 'gate' field is sufficient to allow (or prevent) the propagation of subsequent 'signal' photons along the wire.