Interference in double-slit with single photons

[Byron Forbes]

My question is about how the interference patterns work in a double-slit experiment when firing individual photons through either slit.

Classic - there is 1 photon - it has nothing to interfere with.
Quantum - even with a photon going through each slit at the same time, the likelihood of them converging on the detection plate and interfering might as well be zero.

So what are we seeing?

Obviously, there are zillions of other photons in the room, of varying wavelength, to pass through the slits at any time we fire one from our photon gun. Mustn't it be so that what we see is the constructive and de-constructive interference of our fired photon with all the other ones passing through the slits at the same time and direction?

Has the ambient EMR (basic light in the room) ever been taken into account in these experiments?

 

[PeroK]

Has the ambient EMR (basic light in the room) ever been taken into account in these experiments?

Modern experimental physics may be slightly more advanced than you imagine.

https://aapt.scitation.org/doi/full/10.1119/1.4955173

 

[DrChinese]

My question is about how the interference patterns work in a double-slit experiment when firing individual photons through either slit.

...

Has the ambient EMR (basic light in the room) ever been taken into account in these experiments?

You are completely ignoring the main issue in a double slit experiment. That being: when you know which slit a photon goes through (or could know), there is no interference. If the background radiation were an issue (which our good experimental scientists of course know to eliminate), then there would never be a change in the pattern.

So logic dictates that you should perhaps read a detail explanation of such experiments before you try to guess what the professional scientists forgot to consider. In addition to PeroK's reference, here is one:

https://arxiv.org/abs/1602.05987

Abstract:
As normally used, no commercially available camera has a low-enough dark noise to directly produce video recordings of double-slit interference at the photon-by-photon level, because readout noise significantly contaminates or overwhelms the signal. In this work, noise levels are significantly reduced by turning on the camera only when the presence of a photon has been heralded by the arrival, at an independent detector, of a time-correlated photon produced via parametric down-conversion. This triggering scheme provides the improvement required for direct video imaging of Young's double-slit experiment with single photons, allowing clarified versions of this foundational demonstration. Further, we introduce variations on this experiment aimed at promoting discussion of the role spatial coherence plays in such a measurement. We also emphasize complementary aspects of single-photon measurement, where imaging yields (transverse) position information, while diffraction yields the transverse momentum, and highlight the roles of transverse position and momentum correlations between down-converted photons, including examples of "ghost" imaging and diffraction. The videos can be accessed at this http URL online.

 

[Byron Forbes]

Let me be more specific here before we continue.

I have no interest in experiments with detectors, mirrors, half silvered mirrors or any other junk. I have no interest in whether this is any sort of proof or example of the pattern disappearing or not. Read my question and see the simplicity of the experiment I defined.

Let me be more specific.

My only interest is how a single instance of constructive interference can take place.

So we shoot our photon and it ultimately is seen to land in the middle of one of the bands (constructive interference).

Now, the question is very simple - where does the other photon come from that it interferes with?

Is QM saying that there are infinitely many possibilities for our photon, so all can exist up to and including the moment a specific event occurs, so it's partner went through the other slit and is now interfering with it, and then both immediately vanish?

 

[StevieTNZ]

Now, the question is very simple - where does the other photon come from that it interferes with?

There is no other photon that enters the picture. The one photon (quantum system) in question interferes with itself.

As you may already know, it takes a number of photons interfering with themselves to build up a picture that shows constructive and destructive interference.

 

[Byron Forbes]

There is no other photon that enters the picture. The one photon (quantum system) in question interferes with itself.

So how does a photon interfere with itself? Are you talking about it's quantum pair that went through the other slit?

 

[StevieTNZ]

So how does a photon interfere with itself? Are you talking about it's quantum pair that went through the other slit?

No pairs. One photon, acting as a wave (not in the classical sense) going through both slits.

 

[StevieTNZ]

No pairs. One photon, acting as a wave (not in the classical sense) going through both slits.

I would point out at this point, you may be best to read a book called "Sneaking a Look at God's Cards". You might find that beneficial to your understanding of quantum theory at a laymen level.

 

[Byron Forbes]

Ok, though I find this answer unacceptable, we are at least getting somewhere and I get the general idea of what QM is saying i.e. that no other photons are interfering with our photon.

So what is wrong with the following interpretation?

There are zillions of other photons (ambient light) passing through the slits in the same direction and at the same time as our photon. On the whole and on average, they can be thought of as being of a specific wavelength and so the way our photon interacts with them, on average, could be expected to yield an interference pattern.

Why is this suggestion invalid?

 

[StevieTNZ]

Why is this suggestion invalid?

The experimental set-up would take into account any other photons coming into the setup.
as per

I get the general idea of what QM is saying i.e. that no other photons are interfering with our photon.

 

[Byron Forbes]

The experimental set-up would take into account any other photons coming into the setup.
as per

How so?

 

[StevieTNZ]

I'm not an experimental physicist so I wouldn't know the technical details. Perhaps someone can help explain a bit more behind the setup.

 

[Byron Forbes]

Also, let's even consider the following.

At the moment we fire our photon, what is so special about it compared to all of the other photons in the room, especially the other ones that are about to go through those slits as well and in the same direction?

 

[StevieTNZ]

To be honest, I wouldn't go down that track. Even I got stuck into that topic quite deep years ago and it just gave me tension headaches to the point of nausea. Unless you can cope differently...

 

[Byron Forbes]

And maybe the most important question here, and this really has nothing to do with QM, is that even if we shine a light globe through 2 slits we get an interference pattern. As a matter of fact, we clearly get a diffraction pattern even with 1 slit?

Agreed?

So the massive question is, we are seeing light being deflected here so how is that occurring? Does contemporary science have any explanation for this?

 

[PeterDonis]

we are seeing light being deflected here so how is that occurring?

Quantum mechanics.

Does contemporary science have any explanation for this?

Yes, it's called quantum mechanics.

I strongly suggest taking some time to learn how QM actually works from a textbook; you appear to have some very basic misunderstandings.

 

[PeterDonis]

At the moment we fire our photon, what is so special about it compared to all of the other photons in the room

The fact that it is inside the experimental apparatus, which is carefully shielded by the experimenters so stray photons can't get in. @DrChinese pointed this out way back in post #3.

especially the other ones that are about to go through those slits as well and in the same direction?

There aren't any. See above.

 

[PeterDonis]

The OP questions are based on misunderstandings, which have been corrected. Thread closed.