When a single photon is sent through an interferometer , it passes through both paths , interfering with itself , as waves do .
When a single photon is sent through an interferometer , it is detected by a photomultiplier or other sensitive detector only once .
When a single photon is sent through an interferometer , it passes through both paths , interfering with itself , as waves do , yet is detected by a photomultiplier or other sensitive detector only once .