Biphoton statistic of quantum light generated on a silicon chip
  We demonstrate a silicon-chip biphoton source with an unprecedented quantum cross correlation up to ${\rm g_{si}^{(2)}(0) = (2.58 \pm 0.16) \times 10^4}$. The emitted biphotons are intrinsically single-mode, with self correlations of ${\rm g_{ss}^{(2)}(0) = 1.90 \pm 0.05}$ and ${\rm g_{ii}^{(2)}(0) = 1.87 \pm 0.06}$ for signal and idler photons, respectively. We observe the waveform asymmetry of cross correlation between signal and idler photons and reveal the identical and non-exponential nature of self correlations of individual signal and idler photon modes, which is a nature of cavity-enhanced nonlinear optical processes. The high efficiency and high purity of the biphoton source allow us to herald single photons with a conditional self correlation $\rm g_{c}^{(2)}(0)$ as low as $\rm 0.0059 \pm 0.0014$ at a pair flux of $\rm 1.95 \times 10^5$ pairs/s, which remains below $\rm 0.026 \pm 0.001$ for a biphoton flux up to $\rm 2.93 \times 10^6$ pairs/s, with a photon preparation efficiency in the single-mode fiber up to 51%, among the best values that have ever been reported. Our work unambiguously demonstrates that silicon photonic chips are superior material and device platforms for integrated quantum photonics. 
Xiyuan Lu, Wei C. Jiang, Jidong Zhang, and Qiang Lin
physics.optics quant-ph