這是Scheme of a "two-channel" Bell test
The source S produces pairs of "photons", sent in opposite directions. Each photon encounters a two-channel polariser whose orientation can be set by the experimenter. Emerging signals from each channel are detected and coincidences counted by the coincidence monitor CM.
S同時產生A光子與B光子。光子通過a或b時,偏極被偵測到。四種光子A+,A-,B+,B-經過CM記錄抵達的時間。如果a距離S比b近,A光子抵達a時成為A+光子時,B光子應立即成為B-光子。A+光子與B-光子抵達CM的時間差應該是固定。同樣A-光子與B+光子抵達CM的時間差也應該是固定。
問題是實驗如何證明同時性?