Fig. 4

Evidence of quantum correlations and photon anti-bunching. a Coincidence-to-accidental ratio (CAR) as a function of power for two different choices of the coincidence time window, Δt = 240 ps (red) and Δt = 1.7 ns (green). The dashed lines are simulated for different ratios between Raman and Casimir (DCE) photons on the idler channel. b Intensity auto-correlation function g⁽²⁾(0) at zero delay. The blue dashed line is a simulation assuming only single photon states |1〉 from DCE and Raman photons. All error bars assume a Poisson distribution of the number of coincidence counts, i.e. going as \(\sqrt N\), where N is the measured average number