Figure 4. Special polarization and cooperativity.

Black: numerically determined special polarization angle, where photon bunching in transmission is maximized, as a function of the cooperativity C, which in turn is modified by varying only the QD lifetime γ_||. The green curve is given by the phenomenological expression −45°exp (−C): in the limit of high C, the QD alone can efficiently filter out single-photon states, leading to photon bunching. However, for low cooperativity C, it is advantageous to mix the quantum-dot scattered light with a ‘local oscillator' provided by orthogonal polarization. The error bars (all s.d.) are due to numerical errors in optimizating the laser frequency. The red data point corresponds to the sample presented here; the blue data corresponds to another device with lower cooperativity.