I What is the current experimental evidence for quantum trajectory theory?

[Demystifier]

TL;DR Summary

Discussion of quantum trajectory theory and recent experimental results related to it.

[Moderator's note: Spin off from previous thread due to topic change.]

Recent experimental confirmation of the quantum trajectory theory: https://www.quantamagazine.org/how-quantum-trajectory-theory-lets-physicists-understand-whats-going-on-during-wave-function-collapse-20190703
/?fbclid=IwAR2N8A8F9va2d7NzLh_WWmS54UWYJsY7FXI4CwVq9DzM1VxfsjCIgIYzQgU#
Could be relevant to the Neumaier's theory.

 

[PeterDonis]

Recent experimental confirmation of the quantum trajectory theory

Does anyone have a link to the actual paper? As usual with science journalists, the Quanta article doesn't reference the actual paper, and such articles often make things seem far more sensational than they actually are.

 

[akhmeteli]

Does anyone have a link to the actual paper? As usual with science journalists, the Quanta article doesn't reference the actual paper, and such articles often make things seem far more sensational than they actually are.

https://www.nature.com/articles/s41586-019-1287-zprobably also relevant: https://arxiv.org/abs/1902.10355

 

[akhmeteli]

Does anyone have a link to the actual paper? As usual with science journalists, the Quanta article doesn't reference the actual paper, and such articles often make things seem far more sensational than they actually are.

This is the preprint, I guess: https://arxiv.org/abs/1803.00545

 

[ftr]

https://www.nature.com/articles/s41586-019-1287-zprobably also relevant: https://arxiv.org/abs/1902.10355

Simple 1 minute googling for quantum trajectory theory came up with many of these papers. But why the titles seem to be so far away of an expression to the main claim, why be so bashful.

 

[A. Neumaier]

Recent experimental confirmation of the quantum trajectory theory: https://www.quantamagazine.org/how-quantum-trajectory-theory-lets-physicists-understand-whats-going-on-during-wave-function-collapse-20190703
/?fbclid=IwAR2N8A8F9va2d7NzLh_WWmS54UWYJsY7FXI4CwVq9DzM1VxfsjCIgIYzQgU#
Could be relevant to the Neumaier's theory.

Does anyone have a link to the actual paper? As usual with science journalists, the Quanta article doesn't reference the actual paper, and such articles often make things seem far more sensational than they actually are.

It is the paper already discussed in depth here on PF. Quantum jumps in simple quantum systems have long been experimentally observed and pose a challenge to a pure ensemble interpretation, but not to the thermal interpetation, where states are associated with single quantum systems.

 

[Demystifier]

Quantum jumps in simple quantum systems have long been experimentally observed and pose a challenge to a pure ensemble interpretation

What do you mean by pure ensemble interpretation? The interpretation by Ballentine?

 

[PeterDonis]

Is there a reference that explains what "quantum trajectory theory" is? I see it referred to in some of these papers, but none of them explain what it actually is.

 

[Lord Jestocost]

Maybe, this one: Todd A. Brun, "A simple model of quantum trajectories" https://arxiv.org/abs/quant-ph/0108132

 

[A. Neumaier]

What do you mean by pure ensemble interpretation? The interpretation by Ballentine?

Any interpretation that postulates (rather than claims ignorance) that quantum mechanics says nothing about individual systems but is only about ensembles ofsimilarly prepared systems.

Thus vanhees71's view, Ballentine's book (but not his 1970 article, which compromises and is not pure), Peres' book (Peres, however, admits reservations about its application to macroscopic systems).

 

[Lord Jestocost]

I don’t really get why the so-called “Ensemble Interpretation” is repeatedly discussed on this forum. The Ensemble Interpretation suffers from a severe inconsistency as it refuses to answer a simple physical question. As Abner Shimony remarks in “Symposia on the Foundations of Modern Physics 1992 - The Copenhagen Interpretation and Wolfgang Pauli” (edited by K. V. Laurikainen and C. Montonen):

“There is, for example, Ballentine, whom I mentioned yesterday. He says: ‘I am not a hidden variable theorist, I am only saying that quantum mechanics applies not to individual systems but to ensembles.’ I didn't put this down separately because I simply do not understand that position. Once you say that the quantum state applies to ensembles and the ensembles are not necessarily homogeneous you cannot help asking what differentiates the members of the ensembles from each other. And whatever are the differentiating characteristics those are the hidden variables. So I fail to see how one can have Ballentine's interpretation consistently. That is, one can always stop talking and not answer questions, but that is not the way to have a coherent formulation of a point of view. But to carry out the coherent formulation of a point of view, as I think Einstein had in mind, you certainly have to supplement the quantum description with some hypothetical extra variables.”

 

[vanhees71]

Does anyone have a link to the actual paper? As usual with science journalists, the Quanta article doesn't reference the actual paper, and such articles often make things seem far more sensational than they actually are.

Theres a paper in Nature (who gave fotunately up to forbid preprints recently!):

https://arxiv.org/abs/1803.00545

but also the entire thesis of the first author on arXiv:

https://arxiv.org/abs/1902.10355

If somebody is interested in a version with a readable font and usual single-spaced lines, contact me. I made the (small) effort to download the LaTeX sources and reformatted it ;-)).

I've not found the time to study it thoroughly enough to comment on it. It's not clear to, whether this is a new theory or QT applied to the system+measurement device, describing the interaction between the system and measurement device as an effective stochastic process, i.e., a specific application of the theory of open quantum systems. If I understood the enigmatic popular-science article at the quantummagazine site correctly it's the latter type. Also the paper cited in #9 seems to say right that.

If that's the case, I don't see where this should contradict in any way the minimal interpretation, but let's not get into this debate again.

 

[Demystifier]

Maybe, this one: Todd A. Brun, "A simple model of quantum trajectories" https://arxiv.org/abs/quant-ph/0108132

This is really instructive, thank you for bringing this in.

 

[Demystifier]

I don’t really get why the so-called “Ensemble Interpretation” is repeatedly discussed on this forum. The Ensemble Interpretation suffers from a severe inconsistency as it refuses to answer a simple physical question. As Abner Shimony remarks in “Symposia on the Foundations of Modern Physics 1992 - The Copenhagen Interpretation and Wolfgang Pauli” (edited by K. V. Laurikainen and C. Montonen):

“There is, for example, Ballentine, whom I mentioned yesterday. He says: ‘I am not a hidden variable theorist, I am only saying that quantum mechanics applies not to individual systems but to ensembles.’ I didn't put this down separately because I simply do not understand that position. Once you say that the quantum state applies to ensembles and the ensembles are not necessarily homogeneous you cannot help asking what differentiates the members of the ensembles from each other. And whatever are the differentiating characteristics those are the hidden variables. So I fail to see how one can have Ballentine's interpretation consistently. That is, one can always stop talking and not answer questions, but that is not the way to have a coherent formulation of a point of view. But to carry out the coherent formulation of a point of view, as I think Einstein had in mind, you certainly have to supplement the quantum description with some hypothetical extra variables.”

I would say that the ensemble interpretation adherents just feel that minimalism is more important than consistency. They, of course, do think that QM has something to say about individual systems, but they also sometimes deny that QM has something to say about individual systems. The denial is their strategy to escape from the occasional need to say something more specific about individual properties, beceause if they said something more specific they would ruin the ideal of minimalism.

 

[vanhees71]

Well, then you get into the discussion what's the meaning of probabilities for individual events and a battle between "frequentists" and "Bayesianists". A great read, I stumbled over yesterday, is this:

http://www.phy.pku.edu.cn/~qhcao/resources/class/QM/PTO000070.pdf