Coherent generation of non-classical light on a chip via photon-induced tunnelling and blockade

Quantum dots in photonic crystals are interesting because of their potential in quantum information processing(1,2) and as a testbed for cavity quantum electrodynamics. Recent advances in controlling(3,4) and coherent probing(5,6) of such systems open the possibility of realizing quantum networks originally proposed for atomic systems(7-9). Here, we demonstrate that non-classical states of light can be coherently generated using a quantum dot strongly coupled to a photonic crystal resonator(10,11). We show that the capture of a single photon into the cavity affects the probability that a second photon is admitted. This probability drops when the probe is positioned at one of the two energy eigenstates corresponding to the vacuum Rabi splitting, a phenomenon known as photon blockade, the signature of which is photon antibunching(12,13). In addition, we show that when the probe is positioned between the two eigenstates, the probability of admitting subsequent photons increases, resulting in photon bunching. We call this process photon-induced tunnelling. This system represents an ultimate limit for solid-state nonlinear optics at the single-photon level. Along with demonstrating the generation of non-classical photon states, we propose an implementation of a single-photon transistor(14) in this system.