Young’s slits, one photon at a time
Send the photons one at a time, then by the thousands. Then turn on the detector that reveals which slit each photon goes through, and start again.
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What just happened (read it after the experiment)
Each photon lands at one precise spot, like a particle. Yet as they pile up, they draw fringes, like a wave that went through both slits at once.
As soon as a detector records which slit each photon goes through, the fringes vanish. It is enough for the information to exist somewhere, even if nobody reads it.
Richard Feynman saw in this experiment “the only mystery” of quantum mechanics. In 1989, Akira Tonomura carried it out with electrons, sent one at a time.
More experiments
Sources
- Thomas Young, 1804.
- Akira Tonomura et al., “Demonstration of single-electron buildup of an interference pattern,” American Journal of Physics, 1989.