Interferometry: Photons Needed for Interference Pattern

[Bob8102]

TL;DR Summary

Number of photons needed to create interference pattern.

If you have, say, a two-mirror interferometer that is producing an interference pattern, how many photons are interfering? Two, or just one?

 

[gentzen]

Just one.

 

[Ibix]

You need a lot of photons to see an interference pattern, but you only need one in the apparatus at any time. Each one gives you a dot on your screen - then you wait until enough dots appear for you to see the pattern.

 

[Drakkith]

If you have, say, a two-mirror interferometer that is producing an interference pattern, how many photons are interfering? Two, or just one?

Only one at a time is needed. The same is true of, say, electrons in the double slit experiment. The current through the slits can be reduced so low that only one electron at a time is passing through the slits. An interference pattern will still be produced, though you still need to accumulate many electrons at the detector over time to build up the observed pattern. After all, a single particle cannot make a pattern.