A new interpretation of Quantum Mechanics

[WernerQH]

Sure, it's easy enough to measure the reception of a photon (well, easier perhaps), but how do you measure/observe the emission of a photon without inferring it via mathematical artifacts?

Yes, photon is a theoretical concept. But in quantum field theory emission is just the time reverse of absorption. And the transfer of energy from an atom to the radiation field and vice versa is surely something physical.

 

[PeterDonis]

Photons do not exist -- emission of radiation as a mathematical artifact:

That's not what I said. Emission of radiation is a physically measurable process. But emission of radiation is not the same as emission of a photon.

Obviously light quanta are still controversial.

Depends on what you mean by "light quanta". You need to be a lot more precise in your usage of terminology.

 

[WernerQH]

Emission of radiation is a physically measurable process. But emission of radiation is not the same as emission of a photon.

Isn't it possible to count individual photons in the laboratory? Aren't they some sort of radiation?

You need to be a lot more precise in your usage of terminology.

I thought I had used the term "photon" as the vast majority of physicists use it. On the other hand I have repeatedly failed to make sense of the distinctions that you deemed necessary concerning "photons" in several other posts of yours. Perhaps it would help if you clarified in an insight article what you perceive as a wide-spread misunderstanding. I'd be happy to use the correct terminology if only I understood what bothers you about how other physicists use the word photon. If you have a deeper understanding, please share it.

 

[PeterDonis]

Isn't it possible to count individual photons in the laboratory?

It is possible to run experiments in which there are discrete detection events that some people describe as "detection of photons". But in most of those experiments, the state of the electromagnetic field is not an eigenstate of photon number and is not usefully described as "photons". The most common such state is a coherent state, which is an eigenstate of the annihilation operator--which means, heuristically, that "detecting a photon" when the field is in this state does not change the field state.

Aren't they some sort of radiation?

Electromagnetic radiation certainly exists, but is not usefully described as "made of photons" except in a very vague and heuristic sense that is seldom useful for actually making predictions.

I thought I had used the term "photon" as the vast majority of physicists use it.

In informal contexts, i.e., where nobody is actually trying to make predictions or teach others how to make predictions, or talk about the foundations of the theories we use to make predictions, physicists do often use the term "photon" loosely. But this is not such a context.

If you have a deeper understanding, please share it.

I have already done so in plenty of those previous threads you refer to. Your suggestion of writing an Insights article, though, is a good one and I will try to do that.

 

[WernerQH]

It is possible to run experiments in which there are discrete detection events that some people describe as "detection of photons". But in most of those experiments, the state of the electromagnetic field is not an eigenstate of photon number and is not usefully described as "photons".

Gamma-ray astronomers have no qualms expressing their results as photon fluxes. And it's surely difficult for them to "prepare" the radiation field in a photon number eigenstate. It's a mystery why you deny the usefulness of reporting their results as photon fluxes. It's the detector counts what they directly measure.

The most common such state is a coherent state, which is an eigenstate of the annihilation operator--which means, heuristically, that "detecting a photon" when the field is in this state does not change the field state.

A coherent state is a theoretician's plaything, because it most closely resembles a classical field. The most common state encountered in nature is a thermal state, which has a vast spread over the energies and nothing of the infinite phase stability of a coherent state. And of course detecting a photon changes the field state, decreasing its energy by ## h\nu ##. It remains in a coherent state only if you think that the radiation field is fully described by a single complex number.

Electromagnetic radiation certainly exists, but is not usefully described as "made of photons" except in a very vague and heuristic sense that is seldom useful for actually making predictions.

Even the Nobel prize committee recognized the usefulness of Einstein's "heuristic viewpoint".

You haven't really explained why "photon" is such a taboo-word for you. You are insisting on terminology that is your own, and certainly not mainstream.

 

[PeterDonis]

Gamma-ray astronomers have no qualms expressing their results as photon fluxes.

Gamma rays are detected as discrete events because of their high energy, so the astronomers are just describing what they detect. You won't find optical or radio astronomers describing what they detect as photon fluxes.

It's the detector counts what they directly measure.

Exactly. And that claim is not a claim that the electromagnetic field they are detecting is made of "photons". It's just a description of counts of discrete detection events. Which is perfectly consistent with what I've been saying.

A coherent state is a theoretician's plaything, because it most closely resembles a classical field. The most common state encountered in nature is a thermal state

Which is, if anything, even less suited to a description in terms of "photons" than a coherent state.

detecting a photon changes the field state, decreasing its energy by ##h \nu##.

Please give a specific reference to support this claim with regard to a thermal state of the EM field (or a coherent state, for that matter).

You haven't really explained why "photon" is such a taboo-word for you.

Yes, I have. I have explicitly said that the word "photon" is fine as a description of discrete detection events, but is not fine as a claim about the state of the EM field. It is very rare to encounter EM field states that are eigenstates of photon number, and only such states are usefully described in terms of "photons". Read my post #214 again: it's right there. You even quoted my statements to that effect.

 

[collinsmark]

Gamma rays are detected as discrete events because of their high energy, so the astronomers are just describing what they detect. You won't find optical or radio astronomers describing what they detect as photon fluxes.​

Not to be nitpicky here, but I think you'll find "photon flux" being spoken of in optical & near-infrared, particularly when discussing the sensor itself. Even in my backyard telescope, which I presently only use to take "pretty pictures" in optical wavelengths, it's essentially counting discrete photon detection events within a specified frequency bandwidth (once quantum efficiency is considered, which in my case can be as high as around 90%, depending on the camera I'm using; and a little ambiguity on top of that due to read noise).

That said, I think I agree with your general claims here. There are two points in-particular on which I'll elaborate:

(1) Photons cannot truly be treated as discrete particles (at least not in a non-lazy way) except at the detection event itself. As an example, take interferometry. The electromagnetic energy must be treated as wavelike up to the point of detection; otherwise interferometry (e.g., the Keck Interferometer and even the double slit experiment for that matter) wouldn't make any sense. But if you define "photons" in a non-lazy way, making them more nuanced quantum particles with both wavelike characteristics before detection and classical particle like properties at detection, then maybe that's what @WernerQH is getting at? I.e., A photon can still be called a "photon," even before detection: before its wavefunction has become an eigenstate of a detection event. It's just that in this sense, a "photon" is more nuanced than a classical particle.​

​

And with that, I should point out to @WernerQH, that if you define a photon in the more nuanced fashion, then all the nuance of it having wavelike properties (e.g., being in more than one place at any given time), is a mathematical artifact of quantum field theory (QFT). None of that nuance can be measured/observed directly.​

(2) I agree that radio astronomers don't describe individual photons that often.​

 

[PeterDonis]

I think you'll find "photon flux" being spoken of in optical & near-infrared, particularly when discussing the sensor itself.

Can you give a reference?

 

[PeterDonis]

After the measurements of the COBE, WMAP, and Planck satellites we even can assign a definite, five-digit number to the photon density of the cosmic microwave background.

Please give a specific reference that uses the term "photon density" in this context.

Why do you invariably (mis-)interpret any sentence containing the word "photon" as a statement about an abstract "state" of the electromagnetic field?

Because that's how you're using the term:

It is not unusual (and perfectly intelligible) to say that a photon carries a certain amount of energy ## h\nu ## from the source to the detector.

This is a claim about the state of the electromagnetic field between the source and the detector. And unless the field is in a Fock state, it's a false claim.

Detecting a photon means that it is absorbed by an atom, exciting it to a higher energy level.

Not all photon detectors are single atoms where we measure a specific transition. In most cases we don't measure anything except a click or a dot, and we have no idea how specifically the photon got absorbed. We certainly don't always measure a specific transition frequency ##\nu##. And as anyone who is familiar with QM should know, you have to be extremely careful making any claims at all about things that are not measured.

 

[collinsmark]

I think you'll find "photon flux" being spoken of in optical & near-infrared, particularly when discussing the sensor itself.

Can you give a reference?

Here's a few.

Wavefront sensing with prisms for astronomical imaging with adaptive optics
"A scenario where a read out noise of 5 electrons is also evaluated and the 3-sided prism WFS is found to have a Strehl ratio 12% higher than that of the pyramid WFS with a photon flux of 5 photons/subaperture/frame."

The Steward Observatory LEO Satellite Photometric Survey
"In addition to visual magnitudes, we also present two new metrics: the expected photon flux and the effective albedo. The expected photon flux metric assesses the potential impact on astronomy sensors by predicting the flux for a satellite trail in an image from a theoretical 1 m class telescope and sensor."

Here's one dealing with photosynthesis related sensors (not astronomy, but it is photon flux related):
Accuracy of quantum sensors measuring yield photon flux and photosynthetic photon flux
No quote necessary, since it's right there in the title.

Here's a product in industry:
Model PMA2132 Digital Quantum Light (PAR) Sensor
"Solar Light’s Model PMA2132 Digital Quantum Light (PAR) Sensor measures the photon flux in wavelength range from 400 to 700 nm."

 

[PeterDonis]

Here's a few

Thanks for the references. From what I can gather, these sensors are actually counting discrete detection events, and "photon flux" is counts per second (or counts per unit area per second). So as long as it is understood that "photon" means "discrete detection event", the use of the term is fine. None of these experiments, as far as I can tell, are on Fock states, so the EM field state would not be aptly described using the term "photon", but none of these references appear to be doing that.

 

[collinsmark]

Thanks for the references. From what I can gather, these sensors are actually counting discrete detection events, and "photon flux" is counts per second (or counts per unit area per second). So as long as it is understood that "photon" means "discrete detection event", the use of the term is fine. None of these experiments, as far as I can tell, are on Fock states, so the EM field state would not be aptly described using the term "photon", but none of these references appear to be doing that.

Yes, of course. They only measure discrete detection events. The same is true of the pixel elements in the sensor of my digital camera.

 

[collinsmark]

Forgive me, but I was sort of pulled into this thread by accident when my post from a different thread got moved here. So when I started commenting it was without the context of the whole first part of this thread. But now I do have a question.

None of these experiments, as far as I can tell, are on Fock states, so the EM field state would not be aptly described using the term "photon",

I'm led to believe that the bosonic creation and annihilation operators in QFT Fock states are non-Hermitian. Now, I'm not at all savvy with QFT (or Second Quantization, hence my question), but is the non-Hermitian property of these operators like that in standard QM, insofar that observable operators must be Hermitian?

I mean if this conversation is about directly observing the bosonic Fock state creation or annihilation, is that possible even in principle?

 

[PeterDonis]

I'm led to believe that the bosonic creation and annihilation operators in QFT Fock states are non-Hermitian.

That's correct.

is the non-Hermitian property of these operators like that in standard QM, insofar that observable operators must be Hermitian?

Yes. The creation and annihilation operators are not observables in themselves. However, there are observables that can be expressed in terms of them (for example, the canonical expressions for position and momentum operators in terms of creation and annihilation operators).

I mean if this conversation is about directly observing the bosonic Fock state creation or annihilation

It isn't. The point is simply that the Fock states are the only ones that are eigenstates of photon number, so they are the only ones that are properly described as consisting of "photons". Preparing such states, and observing them, is a hard experimental problem, but not insurmountable.

What we actually observe when we observe Fock states is an appropriate transition in the detector. The corresponding transition in the field itself is not observed; it is only inferred from the preparation and the detection.

We calibrate sources that prepare Fock states by doing quantum tomography on them--repeated measurements of different kinds to characterize the state that the source is preparing. For example, we can look for particular types of correlation or anti-correlation statistics that only Fock states can produce.