Copenhagen Interpretation - Superposition - confirmed?

[Jacob Peters]

Hi,

From what I read here, they did a double slit experiment test with neutrons that seemed to confirm superposition that the particle was in both places at once. Thoughts?

 

[PeroK]

Hi,

From what I read here, they did a double slit experiment test with neutrons that seemed to confirm superposition that the particle was in both places at once. Thoughts?

To be precise it confirms that the particle is governed by a wavefunction, rather than being one localised particle at all times. It's certainly impressive and a more direct example of superposition than taking a statistical average.

I'd be interested to know whether Bohmian Mechanics would predict the same result? I imagine it must.

 

[PeroK]

PS as all interpretations of QM predict the same experimental results, this result is not specific to Copenhagen or any other interpretation.

 

[Jacob Peters]

To be precise it confirms that the particle is governed by a wavefunction, rather than being one localised particle at all times. It's certainly impressive and a more direct example of superposition than taking a statistical average.

I'd be interested to know whether Bohmian Mechanics would predict the same result? I imagine it must.

Thanks!

I was wondering about Bohmian Mechanics specifically as well. I guess I thought proving superposition -> proving Schrödiger’s Cat -> Proving CI . a bit surprised but not knowing much also not surprised i got it wrong.

what would it take to prove one interpretation over another experiment wise? is it possible anytime soon?

 

[PeroK]

what would it take to prove one interpretation over another experiment wise? is it possible anytime soon?

They all make the same experimental predictions, which is why they are interpretations and not rival theories.

 

[Jacob Peters]

They all make the same experimental predictions, which is why they are interpretations and not rival theories.

you’re going to tell me there’s no “rivalry” between Brohmian, CI, and superdeterminism...lol...

 

[Vanadium 50]

superposition that the particle was in both places at once. Thoughts?

The particle was not in two places at once and QM never says it is.

 

[Jacob Peters]

The particle was not in two places at once and QM never says it is.

seemed like it did. Did you miss this part?:

The photon passing through both slits at once is an example of quantum superposition, an object being in two places simultaneously.

 

[StevieTNZ]

seemed like it did. Did you miss this part?:

Don't think of that in the classical sense. Think of it more as potentialities.

 

[hutchphd]

I am chagrinned to admit that I don't understand what is novel in the result. Yeah it was likely more difficult to do with neutrons. Is there really anything interesting here? (it is in a well-refereed journal). If I get interested I will give it a more detailed read.

 

[Nugatory]

seemed like it did. Did you miss this part?:

No, none of us following this thread missed that part. That iflscience.com piece isn’t there to explain QM, it’s there to sell advertising.

“The particle goes through both slits” is something that you’ll hear a lot from non-serious sources trying to come up with a layman-friendly explanation that doesn’t use the math required for a real explanation. It is terribly misleading (it would be just as accurate to say that the particle “goes through neither slit”) and is one of the first things that you’ll unlearn when you first encounter QM on the way to a degree in physics.

Although it’s no substitute for a real textbook, you might want to give Giancarlo Ghirardi’s book “Sneaking a look at God’s cards” a try. It does a pretty good job of outlining what QM is without requiring that you pay the full mathematical price of admission.

 

[Jacob Peters]

No, none of us following this thread missed that part. That iflscience.com piece isn’t there to explain QM, it’s there to sell advertising.

Then please explain where the scientifical article says part of each neutron took both paths: “As shown before, the path presence it not a statistical aver- age but can be attributed to every single detected neutron. We can exclude the possibility that some neutrons have taken only one path and other neutrons have taken only the other path and that they are distributed over the paths only in a statistical way. The probe qubit would carry on the noise of the path presence, which is not the case. The path presence is precisely measured and it quantifies how each individual neutron was distributed between the paths.” I don’t think you two read that part

 

[Jacob Peters]

Don't think of that in the classical sense. Think of it more as potentialities.

Ok, but they specifically quote mr scientist saying:

“ The results show that individual particles experience a specific fraction of the magnetic field applied in one of the paths, indicating that a fraction or even a multiple of the particle was present in the path before the interference of the two paths was registered,” the paper claims. “The obtained path presence [...] is not a statistical average but applies to every individual neutron.””

how can information come from nowhere for the neutron to decide which path it’s in? how can A -> B if A doesn’t exist? I am not thinking of a classical mechanics view, which from what I understand Brohmian mechanics uses anyway

 

[hutchphd]

The fact that a populizer science journal made silly claims is not unusual.
As I mentioned above I looked at the paper in PRR and I really don't have a clue why it was published at all. Does anyone have a clue?

 

[Jacob Peters]

The fact that a populizer science journal made silly claims is not unusual.
As I mentioned above I looked at the paper in PRR and I really don't have a clue why it was published at all. Does anyone have a clue?

From the paper:

“As shown before, the path presence it not a statistical aver- age but can be attributed to every single detected neutron. We can exclude the possibility that some neutrons have taken only one path and other neutrons have taken only the other path and that they are distributed over the paths only in a statistical way. The probe qubit would carry on the noise of the path presence, which is not the case. The path presence is precisely measured and it quantifies how each individual neutron was distributed between the paths.”

This was known before?

 

[hutchphd]

Final paragraph:

It should be emphasized that all results are completelyconsistent with standard quantum theory. The conclusion thatparticles can be physically delocalized between paths in whichno strong interactions occur and that the localization or delo-calization is decided by a measurement that takes place afterthe particles have propagated along the paths is a possibilityinherent in the paradoxical aspects of quantum superpositions.In the present paper, we demonstrated that standard quantumtheory predicts precise and specific effects of the presence ofa particle in a path, even when the particle only undergoes avery weak interaction on its way though the interferometer.

This does not move the Earth from under my feet. I guess it is worthy of publication on confirmational basis.

 

[StevieTNZ]

As suggested, please read "Sneaking a Look at God's Cards" - https://press.princeton.edu/books/paperback/9780691130378/sneaking-a-look-at-gods-cards. You might be better informed about QM by reading that book.

 

[DrChinese]

In all fairness, I would say this is an impressive experiment. They demonstrate that the "path not taken" has an influence on the outcome. Of course, that is essentially equally true in any double-slit or interferometer experiment. But in this one, it is demonstrated in every run - you don't need statistical averaging to see the effect of their weak measurement.

By analogy: the GHZ experiment similarly requires only a single run to falsify local realism. When that came along, Bell tests had already excluded local realism. And yet GHZ is still impressive.

https://arxiv.org/abs/2202.00272

 

[Demystifier]

I'd be interested to know whether Bohmian Mechanics would predict the same result? I imagine it must.

Of course.

 

[Demystifier]

you’re going to tell me there’s no “rivalry” between Brohmian, CI, and superdeterminism...lol...

They are rival interpretations, but there is no rivalry in their measurable predictions.

 

[PeroK]

The fact that a populizer science journal made silly claims is not unusual.
As I mentioned above I looked at the paper in PRR and I really don't have a clue why it was published at all. Does anyone have a clue?

It's the fine control over the spin states that I suspect has not been achieved before. In particular control over the relative phase between the spin state in each part of the superposition.

 

[PeroK]

From the paper:

“As shown before, the path presence it not a statistical aver- age but can be attributed to every single detected neutron. We can exclude the possibility that some neutrons have taken only one path and other neutrons have taken only the other path and that they are distributed over the paths only in a statistical way. The probe qubit would carry on the noise of the path presence, which is not the case. The path presence is precisely measured and it quantifies how each individual neutron was distributed between the paths.”

This was known before?

Yes. It's standard QM. As technology improves more detailed experiments are possible to demonstrate the results more clearly. This is precision experimental physics to confirm existing theory. It's not breaking new theoretical ground.

Niels Bohr, the originator of the CI, would have said that asking which path the neutron took without measuring it would be an invalid question. And that QM deals only with what you measure. Between measurements the wavefunction evolves, and the particle cannot be said to be in one place at a given time, nor in two places at a given time.

The "two places at once" is used in popular sources to indicate superposition, but it's not the CI.

 

[CoolMint]

The way they did their 'measurements', wasn't the neutron only weakly 'present' on both paths?

 

[vanhees71]

BTW the understandable scientific paper is open access:

https://doi.org/10.1103/PhysRevResearch.4.023075

 

[CoolMint]

Hi,

From what I read here, they did a double slit experiment test with neutrons that seemed to confirm superposition that the particle was in both places at once. Thoughts?

The take-away seems to be that weak measurements produce weak results, while strong measurements produce strong definite results. And the likely further implication that measurements produce outcomes in contrast with some interpretations which assert that there are outcomes even in the absence of measurements. This assumption may have been shot down by this particular experiment.

 

[Lord Jestocost]

The authors clearly state in their paper "https://doi.org/10.1103/PhysRevResearch.4.023075":

"It should be emphasized that all results are completely consistent with standard quantum theory."

 

[PeterDonis]

they did a double slit experiment test with neutrons that seemed to confirm superposition that the particle was in both places at once

They did a double slit experiment with neutrons that seemed to confirm that neutrons behave exactly like any other quantum particles. Whether that means the neutrons were "in both places at once" is a matter of which QM interpretation you choose, just as for any other quantum particles.

 

[vanhees71]

It's a somewhat misleading statement to say "the neutrons are in both places at once". In this experiment the neutrons are prepared in a state such that they don't take a definite position (or in other words the state is such that the localization of the neutron is uncertain to an extent that it makes no sense to say they are in one or the other arm of the beam splitter). QT tells us that the classical-particle picture is insufficient to describe the neutrons in this case, i.e., you cannot think about them in terms of classical particles which follow (with some accuracy) a certain path. The experiment demonstrates exactly this, and one must be very careful when trying to describe it in every-day language. The only precise language is the mathematical formalism of quantum theory (bras, kets, operators, wave functions, and all that).