Sunday 24 May 2020

quantum mechanics - Does a photon interfere only with itself?


I sometimes hear statements like:



Quantum-mechanically, an interference pattern occurs due to quantum interference of the wavefunction of a photon. The wavefunction of a single photon only interferes with itself. Different photons (for example from different atoms) do not interfere.



First of all -- is this correct?



If it is correct -- how do we explain basic classical interference, when we don't care about where the plane waves came from?


I heard that there are experiments with interference of two different lasers -- is this considered as a refutation of the statement? If it is -- how should one formally describe such a process of interference of different photons?


Finally -- such statements are usually attributed to Dirac. Did Dirac really say something like that?




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