Figure 2
From: Four-dimensional entanglement distribution over 100 km
Result of photon detection time tracking. Histograms of single photon counts in long-time measurements at SNSPD 2 for Alice are shown. Single photon counts were accumulated in one minute for each histogram. The photon detection time drifted about 4 ns during the measurement, which was longer than the total duration of the four-dimensional time-bin state.
