In the delayed-choice quantum eraser, why is a stepper motor used?

[murtazashab]

It appears to misunderstand the notion of the detectors D3, D4 providing path information and affecting the results D0.

My question is: When there is no path information being provided, why does the experiment still call for moving D0?

I understand that by moving D0 we can modify the arrival time of the idler photon.

I don't understand, why when there is no path information being provided at D3,D4 do we need to still move D0 in order to obtain an interference pattern.

"During an experiment, detector D0 is scanned along its x axis, its motions controlled by a step motor. A plot of "signal" photon counts detected by D0 versus x can be examined to discover whether the cumulative signal forms an interference pattern. "

Source: https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

Why doesn't an interference pattern occur at a stationary D0, when there is no path information being provided at D3,D4?

 

[Nugatory]

Why doesn't an interference pattern occur at a stationary D0?

If the detector remains at a single point then all we get is the intensity at that point. An interference pattern is different intensities at different points, so we need to measure at multiple points.

 

[murtazashab]

@Nugatory thanks for response let me try this. ... Appreciated your efforts...