Combined polarisation measurement of Alice and Bob – The detectors „Alice“ and „Bob“

The two-door metaphor symbolises an important experiment with pairs of photons in quantum optics. The polarisation of the pairs of photons is measured in the following experimental set-up. On Alice and Bobs side, there are a polarisation rotator, a polarising beam splitter and two detectors, respectively.

The “White” detector registers the transmitted photons – door open – and the “Black” detector reflected photons – door closed. Depending on the relative position of the polarisation rotators, the correlation between the measurements of “Alice” and “Bob” gradually changes from correlation to anti-correlation.