Fig. 1.

Bomb testing with a Mach—Zehnder interferometer operated with a single photon at a time. The beam splitters have split ratio 50:50. a The phase difference between the two arms is adjusted such that all photons are directed to detector D2. The object situated close to the lower branch B (e.g., a dud bomb not equipped with the trigger) does not intercept the photons. b The object (e.g., a “live bomb” equipped with an avalanche photodiode which is triggered by a single photon 1) intercepts the photons in the lower branch B