Ultra-low power optical transistor using a single quantum dot embedded in a photonic wire

Summary form only given. Optical logic down to the single photon level holds the promise of data processing with a better energy efficiency than electronic devices [1]. In addition, preservation of quantum coherence in such logical components would enable optical quantum logical gates [2-8]. Optical logic requires optical non-linearities to allow for photon-photon interactions. Non-linearities usually appear for large intensities, but discrete transitions in a well coupled single two-level system allow for giant non-linearities operating at the single photon level.This is achieved by engineering what has been coined a "one-dimensional atom" [2], wherein a light emitter is predominantly coupled to a single propagating spatial mode. This favored coupling with a traveling mode is obtained either in a resonant optical cavity [3,4] or with non-resonant field confinement such as in single mode waveguides [5,6] or through the interaction with a focused optical beam [7,8] . Here we take advantage of the large coupling efficiency and the broadband operation of a photonic wire containing a semiconductor quantum dot (QD) [9] to implement a transistor using two different optical QD transitions. Our system is made of a single InAs QD embedded in a GaAs tapered photonic wire (fig. 1a). This system, in which the QD is efficiently coupled to a single guided mode, has been exploited to realize ultrabright single-photon sources [9]. We exploit here its broad operation bandwidth (>100 nm around 950 nm) to efficiently address two different transitions of the QD with two different laser beams to implement a two-color giant non-linearity: a weak probe laser has its reflectivity controlled by a few photons of the control laser.