Please buy the book "Quantum Divide" written by C. C. Gerry & K. M. Bruno which was published from Oxford University Press recently.
Please see the figure 3.9 on page 66.
Think a rectangular configuration.
The interferometer consists from BS1 at left upper corner, Mirror1 at right upper corner, Mirror2 at left lower corner and BS2 at right lower corner.
In between the Mirror 2 and BS2 is the "Pockels cell" which diverts the photon to sideway by certain angle. BS is for Beam Splitter. It reflects and is transperarnt to the incident photon by 50 % each.
I don't understand what is so amazing.
The Pockels cell intercepts the wave function that is travelling CCW path, so that only the wave function that propergated via the CW path is available to and incident on the BS2.
So that the which path information naturally must be definite, and the interfrometry fringe must be lost!
What is so exciting about this "delayed choice experiment"?
Please someone explain me.
An amature physicist
May 19, 2013