Poisson spot with single photons

[Quant]

I suppose that when carried out a Poisson spot with photons one at a time
should have to be observed.
I tried to find such experiment but i got 0 result. it seems that nobody cared
about that. But i think such experiment would be very important as it will show
that the wavefunction can have macroscopic dimension (not just 0.5 mm but
much more).
So why there are not experiments for Poisson spot with single photons?

 

[pines-demon]

I found a poster about it: https://digitalcommons.cwu.edu/source/2020/COTS/96/

 

[Quant]

Thank you

I found a poster about it: https://digitalcommons.cwu.edu/source/2020/COTS/96/

Thank You @pines - demon. As far as I interprete the data the obscuring disc diameter is 4 cm.
Do you think this diameter can be greater? In my opinion the wavefunction of a photon should be
a sphere with R=c.t so much greater diameter should be possible in principle. Then the Arago
spot may be possible with opposite points/parts of the sphere using mirrors if this is true, do you think?

 

[Vanadium 50]

If you think it is important, why not do the experiment yourself? That's probably more effective than complaining on a message board that physicists are all out measuring what they are interested in instead of what you are interested in.

 

[Nugatory]

Thank you

Thank You @pines - demon. As far as I interprete the data the obscuring disc diameter is 4 cm.
Do you think this diameter can be greater? In my opinion the wavefunction of a photon should be
a sphere with R=c.t so much greater diameter should be possible in principle.

"Wavefunction of a photon" is a somewhat tricky idea, in part because when we're talking wavefunctions we're usually talking non-relativistic QM - and photons are among the most egregiously relativistic things around. But with that said, there is no reason to doubt that the probability distribution that leads to dot-at-a-time interference patterns in single-photon experiments can be calculated in the same way no matter the diameter of the sphere.
And that's why there's not a lot of interest in actually doing the experiment with larger spheres: it's a lot of work with small chances of learning anything we didn’t already know.

Then the Arago
spot may be possible with opposite points/parts of the sphere using mirrors if this is true, do you think?

Now this I totally do not understand. Where do mirrors come into it? What experimental setup are thinking of, and having calculated the expected result, what do you expect to learn from this setup.

 

[pines-demon]

Thank you

Thank You @pines - demon. As far as I interprete the data the obscuring disc diameter is 4 cm.
Do you think this diameter can be greater?

If I understand the graph correctly the diameter of the spot is 1 cm.

In my opinion the wavefunction of a photon should be a sphere with R=c.t so much greater diameter should be possible in principle.

Physically yes, in practice it depends, one would have to take a look at the experimental set-up, but I am no good at interpreting optics experiments, see other comments.

 

[Quant]

If you think it is important, why not do the experiment yourself? That's probably more effective than complaining on a message board that physicists are all out measuring what they are interested in instead of what you are interested in.

Short answer: money, time, lot of efforts. But as in fact the classical EM wave is a collection of the separate single photon's "wavefunctions"/probabilties, a classical experiment is also a confirmation for the spherical propagation of "WF"/Pr of single photons.

 

[Quant]

If I understand the graph correctly the diameter of the spot is 1 cm.

Physically yes, in practice it depends, one would have to take a look at the experimental set-up, but I am no good at interpreting optics experiments, see other comments.

1 cm? Why? The shadow spreads from -20 mm to 20 mm. Or i don't take in account the distance behind the disk/ball they used?
I got the idea the Arago spot should exist by solar eclipse? Any info?

 

[Quant]

"Wavefunction of a photon" is a somewhat tricky idea, in part because when we're talking wavefunctions we're usually talking non-relativistic QM - and photons are among the most egregiously relativistic things around.

Yes surely though there are some variants like Byalnizki-Birula, Sipe etc.

But with that said, there is no reason to doubt that the probability distribution that leads to dot-at-a-time interference patterns in single-photon experiments can be calculated in the same way no matter the diameter of the sphere.

Do you agree that as the EM wave is a collection of single photon's probabilities, classical (e.g. huge number of photons) Arago spot experiments confirm the spherical spreading of probability for single photons?
Do you have opinion about Arago spot by solar eclipse?

And that's why there's not a lot of interest in actually doing the experiment with larger spheres: it's a lot of work with small chances of learning anything we didn’t already know.
Now this I totally do not understand. Where do mirrors come into it? What experimental setup are thinking of, and having calculated the expected result, what do you expect to learn from this setup.

If the probability spreads like a sphere (for a source of the photon - a free stationary atom) than probabilities from the opposite ends of that sphere should be able to interfere but mirrors are needed to direct them in one point. Of course this maybe done with fiber optics. Expected result is confirmation of spherical propagation of probability for single photon.
As you think this is completely sure I would say that in all books (say 20) i read on QM there is not a word about how does the probability propagation of single photons look like.

 

[Vanadium 50]

Short answer: money, time, lot of efforts

That's fine, but don't expect people to be convinced by the argument "my time is too valuable. Your time, on the other hand...."

Or, in another context: "Asps. Very dangerous. You go first."

 

[Vanadium 50]

Further, the classical version of this is done by freshman university students. If you want to do this one photon at a time, you start with that, add a dark box, a digital camera, an optical filter, and some stacking software of the kind used by amateur astronomers. That's it.

You don't need a particle accelerator, or a nuclear reactor, or a rocket, or even a vacuum chamber.

 

[Vanadium 50]

I got the idea the Arago spot should exist by solar eclipse? Any info?

Another "it's too much work for me to do - you guys do it!"

You had two options:
A. Plug in the numbers into the equation Wikipedia gives you.
B. Type that into Google.

Again, you decided your time was too important, but our time isn't. How to win friends and influence people.

The answer is "no", as the sun is not even remotely close to the light source requirements.

 

[Quant]

The answer is "no", as the sun is not even remotely close to the light source requirements.

What requirements are you talking about? Every photon from the visible sun disk should
propagate on its own with its own 'wave function'/probability distribution which must pass
the both sides of the moon (because its in almost vacuum) and then interfere only with itself.
So the sun disk is a collection of point sources and each must produce an intfr pattern (of
different photons from that point). As the other points don't intf negatively with any other
point there should be a small image of the sun in the centre of the moon shadow. It would
of course be very faint and obscured by many other sources. The non ideal vacuum will also
diminish this Arago spot formation.

 

[Nugatory]

What requirements are you talking about

Coherence if you anticipate a visible pattern predicted by classical wave optics. Single-photon states if you’re thinking of the dot-at-a-time patterns built up by quantum effects.

 

[Vanadium 50]

What requirements are you talking about?

A point source. The sun is not even approximately one.
A smooth target. The moon is not even approximately one.

 

[Vanadium 50]

And as a PS, the reason you don't see the Arago/Poisson/Fresnel Spot in an eclipse is classical, not quantum mechanical.

 

[PeterDonis]

the classical EM wave is a collection of the separate single photon's "wavefunctions"/probabilties

Only in a very, very vaguely heuristic sense.

in all books (say 20) i read on QM there is not a word about how does the probability propagation of single photons look like.

That should be an indication to you that the concept you are trying to use here, to the extent it even makes sense (see above), is not a very useful one.

 

[Quant]

Only in a very, very vaguely heuristic sense.

What is the EM field respective photons in your view?

That should be an indication to you? that the concept you are trying to use here, to the extent it even makes sense (see above), is not a very useful one.

Now what is concept of a photon?

 

[Nugatory]

Now what is concept of a photon?

No substitute for a quantum electrodynamics text, but this is a good I-level start: https://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

 

[weirdoguy]

Now what is concept of a photon?

The problem is that QM is a non-relativistic theory, therefore you should not be surprised that nobody is writing about photons, which are the most relativistic thing you can get.

 

[Quant]

No substitute for a quantum electrodynamics text, but this is a good I-level start: https://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

No substitute for a quantum electrodynamics text, but this is a good I-level start: https://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

Thank you for effort. But in the article the Fock states (and their superpositions)
are presented as photons. Definitely they are very useful in tackling almost any
problem but are just mathematical constructs. Surely the real life photon can
not be born in whole Universe or can be 'comprised' by infinitely great number
of such Fock photons.

 

[Quant]

The problem is that QM is a non-relativistic theory, therefore you should not be surprised that nobody is writing about photons, which are the most relativistic thing you can get.

Yes but there is QED where the real photons are presented as superpositions of unphysical Fock
(number) states. As far as I remember Fock himself pointed that out.

 

[hutchphd]

Yes but there is QED where the real photons are presented as superpositions of unphysical Fock
(number) states. As far as I remember Fock himself pointed that out.

"Real Photons" ??
Please be more specific as to what the distinction is here (at least by your definition). Perhaps this is part of our seeming communication problem here.

 

[Quant]

Maybe you are right. The Fock states are called photons for QED just as a name.
They don't say that they exist. Just the real photons (perceived in detectors and emitted
from atoms) are 'made' by Fock states e.g. QED photons.
This terminology is very misleading. I don't see anywhere in the text that to be stressed
just in contrary. Silently the imaginations are maintained that these the only photons.
Note that also the real QFT fields are regarded (or at least there is such imprint) to
consist of Fock photons.

 

[hutchphd]

Note that also the real QFT fields are regarded (or at least there is such imprint) to
consist of Fock photons.

What does "real" mean in this context? A reference would be a good start. What does "Fock photon" mean?

Silently the imaginations are maintained that these the only photons.

????? Sorry, not following.

 

[Quant]

What does "real" mean in this context? A reference would be a good start. What does "Fock photon" mean?

Are the quantum fields not the only underlying reality? Reference David Tong b.e. and anything in QFT.

????? Sorry, not following.

Of course when QFT fields are real, then quantized by Fock states it it close to mind that
Fock states are what is real. And they are named photons. Ref. your text.
P.S. The Fock states (fixed k vector) are called photons in the text (and not only in it).

 

[Vanadium 50]

Fock states are what is real.

Huh? When I look outside my window the light that strikes my eye is not real?

This thread seems to have drifted, and in a kind of...um...iconoclastic direction.

 

[Quant]

Please read my post in its entirety. Do not put sentences out of context.
What I'm saying is that Fock states are not real physical beings but mathematical
constructs.
Very obvious is this also in this example. Let a light that one sees is generated,
by at least two atoms. According Fourier each mode will comprise EM
components of the fields generated by these two atoms. E.g. the Fock states
are mix from two sources. Can a photon come from two sources?
I would like to see some physical arguments if possible but not sematic
qualifications. Such remarks don't clear any scientific problem.
Of course anyone is in his own right to stick to wrong but deeply accepted
notions.

 

[Vanadium 50]

Of course anyone is in his own right to stick to wrong but deeply accepted
notions.

I think you are crossing the line between asking a question and promoting your own personal theory. (Which we do not do)

The question in the OP was answered. It was even pointed out that you could demonstrate this yourself. You weren't interested in that, which is your choice. Then we went down this long path that has little to do with the original question and seems to have contradictory claims from you: Fock states are real, Fock states are not real.

If people are confused, it's not because they are not reading what you write. It's that they are.

 

[Nugatory]

Very obvious is this also in this example. Let a light that one sees is generated,
by at least two atoms. According Fourier each mode will comprise EM
components of the fields generated by these two atoms. E.g. the Fock states
are mix from two sources. Can a photon come from two sources?

Sure, why not? It’s a quantized excitation of the electromagnetic field, and that field is coming from two sources.
Now if photons had positions and trajectories you would have a convincing example - a trajectory has to have a single starting point - but they don’t.

 

[Quant]

I think you are crossing the line between asking a question and promoting your own personal theory. (Which we do not do)

The question in the OP was answered. It was even pointed out that you could demonstrate this yourself. You weren't interested in that, which is your choice. Then we went down this long path that has little to do with the original question and seems to have contradictory claims from you: Fock states are real, Fock states are not real.

If people are confused, it's not because they are not reading what you write. It's that they are.

Where did I say Fock states are real? No, the text Nugatory send me says this.

 

[Quant]

Sure, why not? It’s a quantized excitation of the electromagnetic field, and that field is coming from two sources.
Now if photons had positions and trajectories you would have a convincing example - a trajectory has to have a single starting point - but they don’t.nk

Thank you about that physical argument.
And what about billion of sources? Does a photon come from billion sources? (Easy to
be distinguish on time scale in principle)
Can you also explain the immediate spreading of Fock states through the whole space?
Photons can be very well localized at the moments of creation and annihilation.

 

[Vanadium 50]

Where did I say Fock states are real?

Message #26.

 

[Nugatory]

And what about billion of sources? Does a photon come from billion sources? (Easy to
be distinguish on time scale in principle)

Sure, why not? They're associated with the electromagnetic field, not the charges that are the sources of that field.

Can you also explain the immediate spreading of Fock states through the whole space?

What's to explain? (This question is not flippant. Why, other than some amorphous expectation of yours about how things ought to behave, shouldn't they?)

Photons can be very well localized at the moments of creation and annihilation.

Sometimes they can, especially at annihilation time. But they don't have to be. How, without assuming the existence of things that cannot even in principle be measured, do you localize a photon within the beam of a phased-array radar?

You don't have to like how photons behave. You don't have to like that that behavior doesn't work with any intuitive model of what's "really" happening beyond the experimentally observed facts about electromagnetic fields exchanging energy and momentum with matter. But that's still how they behave, and without a plausible candidate theory that makes predictions different from those of quantum electrodynamics it is a fool's errand to keep demanding more experiments that can only further confirm that QED works within its domain of applicability.

 

[PeterDonis]

What I'm saying is that Fock states are not real physical beings but mathematical
constructs.

All "states" are mathematical constructs. Some of them represent, in our mathematical models, things that can be physically realized. Others don't. But in either case the mathematical model is not the same as reality.

In the case of Fock states, they can be physically realized, but it's not at all easy, and most experiments involving light do not use them. Most experiments involving light use coherent states, because that's what light sources that can be easily made produce.