Optical nonlinearity with few-photon pulses using a quantum dot-pillar cavity device

A single two-level system constitutes an extremely non-linear optical medium, where the interaction with a first single photon modifies the transmission probability for a second photon. The main difficulty to implement a single photon switch using this property is to ensure that a gate single photon will interact with the quantum emitter with a near-unity probability. In the solid state, all-optical switching has been demonstrated using photonic crystals or microdisks coupled to quantum dots, but these systems were not well externally matched: hundreds of incident photons were thus required to trigger the optical nonlinearity.