Injection locking of quantum-dot microlasers operating in the few-photon regime

We experimentally and theoretically investigate injection locking of quantum dot (QD) microlasers in the regime of cavity quantum electrodynamics (CQED). We observe frequency locking and phase-locking where cavity-enhanced spontaneous emission enables simultaneous stable oscillation at the master frequency and at the solitary frequency of the slave microlaser. Measurements of the second-order autocorrelation function prove this simultaneous presence of both master and slave-like emission, where the former has coherent character with g(2)(0) = 1 while the latter one has thermal character with g(2)(0) = 2. Semiclassical rate equations explain this peculiar behavior by cavity enhanced spontaneous emission and a low number of photons in the laser mode