Figure 8: Comparison between an obstructed and attenuated beam.
From: Self-healing of quantum entanglement after an obstruction
Measurements of the coincidence count rate, quantum contrast and concurrence of obstructed (a–c) and attenuated (d–f) entangled photons for |ℓ=±2›. The obstruction was moved in 5 mm intervals along the propagation axis, at which the measurements were recorded. The dashed yellow line represents zmin, the calculated distance at which recovery is expected (recovery is not expected within the yellow shaded region). A polarizer was rotated to attenuate the coincidence count rate and vary the degree of transmission from 0 (background levels) to 1 (unattenuated and unobstructed). The coincidence count rates and quantum contrast represent the average of 10 measurements. The average error for the concurrence is ±0.01, which is calculated by generating additional data sets by adding 
fluctuations to the measured coincidence counts Ci and then repeating the concurrence calculations described in the text. The unobstructed concurrence value is represented by the blue dashed lines.
