Extended Data Figure 2: Examples of data showing interference contrast.

Plots of P₁ versus experimental trial for 2ħk, 30ħk, 60ħk and 90ħk. The red traces have small values of δT and therefore display interference contrast. As discussed in the main text, we do not observe a stable fringe because of the vibration of the retroreflection mirror. For comparison, the grey traces have large values of δT so that contrast is eliminated, and they therefore show the amount of background amplitude noise in P₁. Panels from left to right as follows. 2ħk: red trace, δT = 0 μs; grey trace, δT = 2 ms. 30ħk: red trace, δT = −15 μs; grey trace, δT = 100 μs. 60ħk: red trace, δT = 0 μs; grey trace, δT = 100 μs. 90ħk: red trace, δT = 1 μs; grey trace, δT = −50 μs.