Double slit mystery in relation to holography and the single slit?

[Zelebg]

What part of double slit mystery remains considering single slit can produce interference pattern as well? Does holography not fully explain those patterns behind any number of slits as a sort of "encoded image" of the slit(s)?

Does the word "focus" have any meaning in these kinds of experiments?

 

[Demystifier]

The double slit "mystery" is a mystery when you consider a single photon, because the detection of a single photon does not show interference, and yet the statistics of many single photons does. To the extent that it is a "mystery" at all, it is a mystery even for a single slit interference.

 

[EPR]

The addition of a second slit highlights the wave nature of 'particles' better.

 

[Zelebg]

The double slit "mystery" is a mystery when you consider a single photon, because the detection of a single photon does not show interference, and yet the statistics of many single photons does. To the extent that it is a "mystery" at all, it is a mystery even for a single slit interference.

What equation makes us think "single photon" equals only one wave? Why wouldn't a single wave interfere with itself like waves usually do?

To the extent that it is a "mystery" at all, it is a mystery even for a single slit interference.

What mystery are you referring to? In holography everything seems to work just perfectly, slits or no slits.

 

[Demystifier]

What equation makes us think "single photon" equals only one wave? Why wouldn't a single wave interfere with itself like waves usually do?

The problem is that a single photon, when detected, appears as a particle with a relatively well defined position, and not as a wave widely expanded in space. And yet the associated wave is widely expanded in space. It looks like a contradiction or at least a puzzle.

 

[Zelebg]

The problem is that a single photon, when detected, appears as a particle with a relatively well defined position, and not as a wave widely expanded in space. And yet the associated wave is widely expanded in space. It looks like a contradiction or at least a puzzle.

There was a problem with explaining the double slit experiment even before single photon were used, some explanations claimed it has something do with observation or measurement and such.

I don't consider wave-particle duality to be the problem here. The problem with the single photon double slit experiment is that single photon should not interfere with itself, but it’s not supposed to be a photon until it gets fully absorbed, so I ask where is the problem then if not photon, but a wave is interfering with itself?

 

[EPR]

The problem with the single photon double slit experiment is that single photon should not interfere with itself, but it’s not supposed to be a photon until it gets fully absorbed, so I ask where is the problem then if not photon, but a wave is interfering with itself?

It's not just a wave. It lands as if it was a localised particle.

 

[Zelebg]

It's not just a wave. It lands as if it was a localised particle.

When it lands, when it gets absorbed, yes. But until then, and at the time it's passing the slits, it's suposed to still be a 'radiation', a wave, not a photon yet. Right?

 

[Demystifier]

but it’s not supposed to be a photon until it gets fully absorbed

Why do you think so?

 

[Zelebg]

Why do you think so?

You do not?

https://en.m.wikipedia.org/wiki/Electromagnetic_radiation
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space...

 

[EPR]

Those are single photons and single photons probably have very very small em wave width(due to very low energy).

 

[Zelebg]

Those are single photons and single photons probably have very very small em wave width(due to very low energy).

Looks like it's wide enough to go through, otherwise it would get absorbed between the slits and there wouldn't be a pattern. Isn't it the wavelength that needs to be in some special relation to the slits separation?

 

[EPR]

Looks like it's wide enough to go through, otherwise it would get absorbed between the slits and there wouldn't be a pattern. Isn't it the wavelength that needs to be in some special relation to the slits separation?

In the double slit it's the probability wave that goes through both slits. Or that's the predominant mode of thinking. It's nonsense but still...

No one understands this. I mean no one.

 

[Demystifier]

You do not?

I do not.

In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space...

In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space...

By my bolding, you see that photons can be propagating too.

 

[Zelebg]

By my bolding, you see that photons can be propagating too.

Never heard of it before. If photons do not exhibit their wave nature while propagating through space, why would you expect them to interfere like waves?

 

[EPR]

You misunderstand - 'photons' travel through space as oscillating EM waves.
If it's just 1 photon in question, that EM wave is extremely tiny in spread.
The photon(EM wave) also has a theoretical probability wave to it that makes it delocalised.
At measurement/observation this whole quantum arrangement becomes a dot(detection).

Photons like ordinary matter have both quantum and classical-like properties depending on the context.

 

[Mentz114]

In the double slit it's the probability wave that goes through both slits. Or that's the predominant mode of thinking. It's nonsense but still...

No one understands this. I mean no one.

Well, nearly no-one.

https://arxiv.org/abs/1103.0100

 

[PeterDonis]

'photons' travel through space as oscillating EM waves

This is not correct; you are either trying to mix together two different theoretical models of light, or conflating two very different kinds of states.

In the classical EM model, which is the most common one people mean when they use the term "oscillating EM waves", there is no such thing as a "photon".

In the QED model, which is the applicable one if you are using the term "photon", states of the quantum EM field that are usefully described as "photon" states are very different from states of the quantum EM field that are usefully described as "oscillating EM waves". Better still would be to use neither ordinary language term and instead specify in math the particular kind of quantum EM field state you are talking about: Fock state, coherent state, etc.

 

[EPR]

Well, nearly no-one.

https://arxiv.org/abs/1103.0100

Optics?

The double slit experiment has been performed with matter as large as C60.
Explain the interference.

 

[Nugatory]

https://en.m.wikipedia.org/wiki/Electromagnetic_radiationIn physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space...

Stuff like this is why Wikipedia is not in general an acceptable source under the Physics Forums rules. The struck-through part above is just plain wrong.

You will also find that it has been removed from the most recent version of the article.

 

[Demystifier]

Never heard of it before. If photons do not exhibit their wave nature while propagating through space, why would you expect them to interfere like waves?

Who said that photons do not exhibit their wave nature while propagating through space?

 

[Zelebg]

Stuff like this is why Wikipedia is not in general an acceptable source under the Physics Forums rules. The struck-through part above is just plain wrong.

You will also find that it has been removed from the most recent version of the article.

I agree, and it's why 'photon' has its own page.

So we ended up talking about semantics, in a way, and I don't think my questions were addressed, or at least I don't get it yet. Let me unpack and focus on the points I am asking about.

Double slit - single photon experiment
Mystery: why is the pattern still there when emitting single photons.

Q1. Why is this a mystery, why would not a single EM wave interfere with itself like other kinds of waves do?Double slit - which way experiment
Mystery: why the pattern disappears when we monitor one of the slits.

Q2. It seems in the holograpy the pattern on the screen behind the slits is just an "encoded inverse-shadow" of the object that is in the "field of view" of the laser beam. Here I'm interested in actual physical arrangement of the experiment to see whether the results are incompatible with what would be expected in holography.

 

[jtbell]

The double slit "mystery" is a mystery when you consider a single photon, because the detection of a single photon does not show interference, and yet the statistics of many single photons does.

Just to make this explicit, you get the same type of "mystery" for a single slit. The only difference is in the shape of the probability distribution for many photons, which corresponds to the difference in the intensity patterns for classical light waves:

Single slit

Double slit

 

[Mentz114]

Optics?

The double slit experiment has been performed with matter as large as C60.
Explain the interference.

Read the paper I cited. QFT gives the correct prediction for 'matter-waves'.

 

[Cthugha]

Double slit - single photon experiment
Mystery: why is the pattern still there when emitting single photons.

Q1. Why is this a mystery, why would not a single EM wave interfere with itself like other kinds of waves do?

I think you are asking the wrong question. The interesting question is why single photons show interference in a double slit and antibunching in a Hanbury Brown-Twiss experiment at the same time. In case you are not familiar with it: The HBT experiment is simply realized by directing a light field to a beamsplitter and placing single-photon-sensitive diodes at both output ports. If you send single photons towards the beamsplitter, you will find that both detectors will never click simultaneously and for each photon only one of the detectors will receive a detection event. This cannot be realized by considering only EM waves. In fact, the detectors can be placed arbitrarily far apart. Even so far apart that they are not within each others light cone.

 

[Zelebg]

I think you are asking the wrong question. The interesting question is why single photons show interference in a double slit and antibunching in a Hanbury Brown-Twiss experiment at the same time. In case you are not familiar with it: The HBT experiment is simply realized by directing a light field to a beamsplitter and placing single-photon-sensitive diodes at both output ports. If you send single photons towards the beamsplitter, you will find that both detectors will never click simultaneously and for each photon only one of the detectors will receive a detection event. This cannot be realized by considering only EM waves. In fact, the detectors can be placed arbitrarily far apart. Even so far apart that they are not within each others light cone.

I don't see a problem with HBT. I would be surprised if a single photon could split in two. It seems there is an assumption that for a photon to interfere with itself it would first need to split, but in holography interference pattern is not the result of wave interference, but wave diffraction, which is simply direction bending of EM wave. So I guess my question about holography can be rephrased: is there anything diffraction can not explain in any of these experiments?

 

[Cthugha]

I don't see a problem with HBT. I would be surprised if a single photon could split in two. It seems there is an assumption that for a photon to interfere with itself it would first need to split, but in holography interference pattern is not the result of wave interference, but wave diffraction, which is simply direction bending of EM wave.

I think you still avoid the relevant problem. A photon certainly carries energy. If the photon is detected, all of the energy arrives exactly at the position of the detector. One may naively assume that the energy travels to the detector in a localized manner. Then the appearance of the double slit pattern is puzzling. One may also naively assume that the energy is somehow delocalized within the wave. In that case at the time of the detection, all the other positions of the wavefront must be "updated" instantaneously in order to ensure that the photon gets detected only once at the position of the detector. In this scenario the double slit pattern is trivial, but you run into problems with relativity and have non-locality as this "update" would happen faster than the speed of light. Of course you may also assume that this property is simply undefined between emission and detection. However, not everybody considers this as a satisfying answer.

 

[Mentz114]

I think you still avoid the relevant problem. A photon certainly carries energy. If the photon is detected, all of the energy arrives exactly at the position of the detector. One may naively assume that the energy travels to the detector in a localized manner. Then the appearance of the double slit pattern is puzzling. One may also naively assume that the energy is somehow delocalized within the wave. In that case at the time of the detection, all the other positions of the wavefront must be "updated" instantaneously in order to ensure that the photon gets detected only once at the position of the detector. In this scenario the double slit pattern is trivial, but you run into problems with relativity and have non-locality as this "update" would happen faster than the speed of light. Of course you may also assume that this property is simply undefined between emission and detection. However, not everybody considers this as a satisfying answer.

With respect, surely using analogies like of wavefronts and updates is old-fashioned, as is looking for mechanisms. The problem is handled in QFT by creating whatever is required in the inputs of the BS and evolving this state. The calculation agrees with experiment but it tells us nothing about a 'mechanism'. Perhaps assuming these things will lead to apparent paradoxes.

 

[Cthugha]

With respect, surely using analogies like of wavefronts and updates is old-fashioned, as is looking for mechanisms. The problem is handled in QFT by creating whatever is required in the inputs of the BS and evolving this state. The calculation agrees with experiment but it tells us nothing about a 'mechanism'. Perhaps assuming these things will lead to apparent paradoxes.

Sure, but this is an I-level thread and I do not think that just saying "QFT handles this well" is going to solve the question. I especially think that it is not needed to understand the problem at hand. Assuming instantaneous updates is just a different name for nonlocality. However, the OP asked the question where the mystery of the double slit is rooted. Of course the math handles the double slit well in the ensemble average and on a probabilistic level. But the intrinsic mystery is that the double slit with single photons already carries all the basic problems of EPR. And this is indeed not a problem of the math, but of its implications: local realism is not a tenable position. I do not want to enter interpretation territory, but the mechanism taking place in a single run is the single mystery here. The math for ensemble averages surely is not. We do know the results pretty well.

 

[PeterDonis]

Moderator's note: Moved thread to the QM interpretations and foundations forum since the thread topic is more about foundations than about the predictions of the QM math.