I sometimes hear statements like that:
Quantum-mechanically, interference pattern occurs due to quantum interference of wavefunction of a photon. 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 do 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 one should formally describe such process of interference of different photons?
Finally -- such statements are usually attributed to Dirac. Did Dirac really say something like that?
Dear Hossein Jafarzadeh,
Single photon double slit experiment clearly shows that photon interfere with itself.
"Each photon then interferes only with itself.
Interference between two different photons never occurs." -----Dirac, Principle of Quantum Mechanics, page-9.
You can check following link for single photon experiment.
http://physics.wm.edu/~evmik/classes/2014_fall_Experimental_Atomic_Physics_251/manual/single-photon-interference.pdf
Dear Hossein,
When Dirac was around, lasers weren't available, and different light sources had to always be assumed to have random phase differences. This is no longer the case now that we have lasers. So, yes, two lasers can interfere with each other. Because all photons in the same laser are exactly the same, the phase difference between a photon in one laser and another photon from another laser is always the same for all the photons. So, you will see an interference pattern. However, the actual pattern will be different every time, appears to be random, and is not controllable, because the actually phase difference is random (but it's the same random number for all the photons).
To sum up, you do get interference, but the pattern is unpredictable.
So Dirac is indeed wrong here, but who can blame him on that? It was 1930 and no one knew at the time a coherent light sources can be realized.
Wrong! Dirac's idea was falsified here: G. Magyar and L. Mandel, “Interference fringes produced by superposition of two independent maser light beams,” Nature (London) 198 (1963), 255.
and there: R.L. Pfleegor and L. Mandel, “Interference of independent photon beams,” Phys. Rev. 159 (1967), 1084.
Please allow me to be absurd; but kindly answer the question available at following link too: https://www.researchgate.net/post/Are_photons_transparent_to_one_another
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