Photon interference and beamforming

[Charles Link]

I am led to believe that there are still some missing pieces to the puzzle. In the last 40 years there have been a couple experiments, where as I recall, they showed interference with a beamsplitter (or beamsplitters) and a single photon. The researchers didn't know before the experiment what the outcome would be. Perhaps there is a standard textbook that covers these topics in detail. @vanhees71 Can you furnish us with a good reference that has most of the latest on the subject, and hopefully is also somewhat easy reading?

Edit: I did a little searching of my own: See https://www.physicsforums.com/threads/interference-of-a-single-photon-in-an-interferometer.920022/ I see this topic has been discussed on Physics Forums in the last couple of years, and the discussion is interesting.

 

[antonantal]

Edit: I did a little searching of my own: See https://www.physicsforums.com/threads/interference-of-a-single-photon-in-an-interferometer.920022/ I see this topic has been discussed on Physics Forums in the last couple of years, and the discussion is interesting.

Post #27 from that topic cites the following statement:
"Interference can occur if two or more different ways to produce the same result cannot be distinguished with the apparatus."

Now let's apply it to the case of two photons that are emitted at exactly the same time from two sources that are in perfect phase sync. At the screen there is no way to tell which photon is which, so they cannot be distinguished and interference will occur.
Does my post #52 describe this correctly?
In other words, do we have a two-photon state which is a superposition of "both photons emitted by first source" and "both photons emitted by second source"?

 

[sophiecentaur]

Now let's apply it to the case of two photons that are emitted at exactly the same time from two sources that are in perfect phase sync.

Isn't this a very unreal scenario? How would you be able to tell that they are emitted at exactly the same time? Not being like little bullets, they cannot be put past a start line with a stop watch. Only when you consider a single photon can you discuss anything "exactly" the same between the two possible paths by the two 'alternative' versions of the photon which interfere with each other.

It's a bit late to be going over the basics of this thread but, just to make sure I have appreciated the principles of the experiments, it seems to me that individual photons are 'gated' through a shutter and then delay adjusted to be equal so that they pass through a slit each. Then, when everything is arranged correctly, a 'conventional' two slit pattern is observed. Is this in any way along the right lines? (I have to apologise if my idea is too much like the RF equivalent.)

 

[antonantal]

@sophiecentaur , you are correct, what I meant by "emitted at the same time" is just that "they are emitted in such a way that they could interfere at the screen".

 

[sophiecentaur]

@sophiecentaur , you are correct, what I meant by "emitted at the same time" is just that "they are emitted in such a way that they could interfere at the screen".

It worries me that it’s such a big IF.
But, once they have shown interference in space then why not also in time? (ie all the other interference phenomena) it all seems to hang on coherence - as ever.