Fig. 3

Experiments carried out with additional channel noise. In a and b, the filled data points refer to experiments performed without added noise. The solid lines correspond to the theory for a particular N. For c and d, the results are only for N = 4, for clarity, as the trend for N = 2, and 8 are the same. d The gated visibility of the state comparison stage for different levels of noise. The uncertainty in the mean photon number per pulse is 1.5%, due to a small drift in coherent source power. The y-axis errors were found to be less than 2% and are therefore hidden by the data points