Figure 4

Fano factor as a function of \(1/t_{\textrm{bin}}\). (a) The Fano factor in dependence of \(t_{\textrm{bin}}\) at different bias voltages \(V_{\textrm{g}}\). The Fano factor is used here as very sensitive indicator for an appropriate choice of the binning rate (bandwidth), as the Fano factor corresponds to the expected value for low binning rates and diverges for higher rates. The transport statistics can be evaluated up to 70 kHz (0.3742 V; dotted blue line) and 175 kHz (0.401 V; dotted orange line). (b) The asymmetry as a function of bias voltage is given by the tunneling rates that were determined in the waiting time distributions in Fig. 2. (c) The strong increase of the Fano factor can be shifted by changing the laser intensity and thus the average photon rate of the on state \(\Gamma _{\textrm{on}}\). (d) By rescaling the binning rate, the results for 0.23 Mcounts/s, 0.82 Mcounts/s, and 1.72 Mcounts/s coincide. The data for 3.8 Mcounts/s are slightly shifted. (e) The critical binning time \(t_{\textrm{bin}}^{\textrm{crit}}\), as obtained from the model, versus the mean photon rate of the off state. (Inset) The dependence of \(\Gamma _{\textrm{on}}\) can be described by \(t_{\textrm{bin}}^{\textrm{crit}}\propto \Gamma _{\textrm{on}}^{-0.8}\) (inset). The threshold photon number \(\tilde{k}\) at which the maximum binning rate can be obtained depends on the average photon rate of the off state \(\Gamma _{\textrm{off}}\) (see solid, dashed and dotted lines).