Can one photon interfere with another photon?

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In summary, the question of whether one photon can interfere with another photon or if each photon can only interfere with itself is still a topic of debate. While Young's double slit experiment seems to suggest that independent photons can interfere, this is a classical experiment and does not fully explain the quantum behavior of light. Higher order coherence measurements, such as the Hong-Ou-Mandel dip, provide evidence for multi-photon interference, but this is a different type of interference than what is seen in the double slit experiment. Ultimately, the answer to this question may vary depending on the specific experiment and setup being used.
  • #71
The longer the thread gets, the more misconceptions are accumulated :-(.

Photons are massless quanta with spin 1. They are as relativistic as it can get, and you cannot apply naive one-particle wave-mechanics ideas from non-relativistic physics, let alone classical particle or wave concepts to them.

First of all, photons have no well-defined position observable in the strict sense. See Arnold Neumaier's Theoretical-Physics FAQ:

http://arnold-neumaier.at/physfaq/topics/position.html

It doesn't matter, in which of the different possible formulations of non-relativistic wave mechanics (position representation, matrix mechanics, or path integrals as integrals over single-particle trajectories) you try to treat photons. It doesn't work!

The only consistent way to treat photons is QED. That's very intuitive, because photons are created and destroyed all the time when interacting with other stuff, and quantum field theory is the way to describe precisely such annihilation and creation processes of quanta.

That QED actually works is demonstrated in many high-precision ways in both high-energy particle physics, where it is part of the Standard Model of elementary particles, which hitherto is the most successful theory ever, and in quantum optics experiments, where particularly photons are used to demonstrate all the features of quantum theory that appear "most weird" from the point of view of classical physics and our every-day schooled intuition like entanglement ("hypercorrelations").

A very nice article on the topic (particularly on the socalled "wave-particle dualism", which is another outdated point of view, which seems to be impossible to kill in the popular-science literature) is the following article on phys.org:

http://phys.org/news/2014-07-particle-optical-qubit-technique-photons.html
 
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  • #72
vanhees71 said:
The longer the thread gets, the more misconceptions are accumulated :-(.
I'm nipping that problem in the bud.

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