I QM: Interesting View - Get the Inside Scoop

[A. Neumaier]

Not sure how this related to the statistical interpretation! They work with representatives of the ensemble, and according to the statistical interpretations, they do not analyse their properties, but those of the ensemble.

They interpret a single time series as giving evidence of temporal properties of the single ion. No ensemble of ions is involved. This is the whole point of probing individual quantum systems. Being able to control and read the state of a single quantum object is the prerequisite of quantum computing.

Are you saying that this disproves the statistical interpretation?

No, only that the statistical interpretation is incomplete since one cannot infer measurable physical properties of single systems without having a postulate that relates these measurable properties to the state.

 

[A. Neumaier]

How good my description of the preparation in terms of the quantum formalism is, is of course itself subject to experimental test.

Then - like in classical mechanics - the state is an objective property that is matched more or less well by your knowledge. Therefore - like in classical mechanics - you should not talk about knowledge (which is manifestly subjective), since there must be a knower.

So, how do you describe the SG experiment (or the experiments by Haroche and Wineland describe in the Nobel foundation's citations)?

You can read my book to find out. I said it here already many times, without getting it across to you, and won't do it again.

The SG experiment is very well understood [...]So where is the problem?

The problem is that instead of answering my questions you are shifting grounds.

I am not talking about the SG experiment, which is done with n ensemble of many identically prepared systems, so that the minimal interpretation applies.

The Nobel prize winning experiment was instead for measuring a single ion in a trap! You did not explain why

when you measure the pointer position you actually measured the state of the trapped ion, because of entanglement. This is pure handwaving since it is neither in your postulates nor is it derived from them in your lecture notes (version of July 22, 2019), as far as I can see. If I missed the derivation of such a fundamental claim, please point me to the relevant page.

 

[martinbn]

They interpret a single time series as giving evidence of temporal properties of the single ion. No ensemble of ions is involved. This is the whole point of probing individual quantum systems. Being able to control and read the state of a single quantum object is the prerequisite of quantum computing.

Yes, that is a valid interpretation, but is different from the statistical one. And it is not the only possible one.

No, only that the statistical interpretation is incomplete since one cannot infer measurable physical properties of single systems without having a postulate that relates these measurable properties to the state.

But that is something that people insist on. Nature doesn't have to be like that. It could be the way the statistical intepretation descibes it, and questions about the individual system may be meaningless.

 

[A. Neumaier]

It could be the way the statistical interpretation describes it, and questions about the individual system may be meaningless.

The 2012 Nobel prize shows that questions about the individual system are not meaningless but can be probed - sometimes even returning a high prestige and cash value.

 

[martinbn]

The 2012 Nobel prize shows that questions about the individual system are not meaningless but can be probed - sometimes even returning a high prestige and cash value.

How?

 

[A. Neumaier]

How?

The prestige and cash value of a Nobel price is well-known. For the probing of individual systems read this:

the description of the Nobelist's work by the Academy:

https://www.nobelprize.org/uploads/2018/06/advanced-physicsprize2012_02.pdf

From the introduction there:

Individual ions can now be manipulated and observed in situ by using photons with only minimal interaction with the environment. In another type of experiment, photons can be trapped in a cavity and manipulated. They can be observed without being destroyed through interactions with atoms in cleverly designed experiments. These techniques have led to pioneering studies that test the basis of quantum mechanics and the transition between the microscopic and macroscopic worlds, not only in thought experiments but in reality. They have advanced the field of quantum computing, as well as led to a new generation of high-precision optical clocks.

 

[martinbn]

The prestige and cash value of a Nobel price is well-known. For the probing of individual systems read this:

From the introduction there:

I still don't get it. Yes, it is phrased using that language, but so is most of QT in a typical text. Are you saying that it cannot be phrased in a statistical intepretation terminology?

 

[A. Neumaier]

I still don't get it. Yes, it is phrased using that language, but so is most of QT in a typical text. Are you saying that it cannot be phrased in a statistical interpretation terminology?

It can be phrased in the language of quantum stochastic processes but not in the language of the minimal statistical interpretation, which has not enough concepts to handle the continuous measurement of individual quantum systems.

 

[martinbn]

It can be phrased in the language of quantum stochastic processes but not in the language of the minimal statistical interpretation, which has not enough concepts to handle the continuous measurement of individual quantum systems.

The minimal statistical interpretation doesn't handle any induvidual systems irrespectively whether there is a continuous measurment or not. What makes this different? Can you easlily describe the actual experiments that cannot be analysed in the statistical interpretation language?

 

[gentzen]

What makes this different?

The meaning of the state is the difference. If the state is only the description of an ensemble of independent identically prepared system, then the state is not able to describe details of an individual system that go beyond what you be true for any identically prepared system.

Can you easlily describe the actual experiments that cannot be analysed in the statistical interpretation language?

Well, an idea could be to distinguish between the state and what you want to assert about the state. Then you could let the unknown state be the description of the individual system, and determine what you can or cannot assert about it based on what you learn from your measurements.

 

[A. Neumaier]

What makes this different? Can you easily describe the actual experiments that cannot be analysed in the statistical interpretation language?

I had said it several times: The fact that only a single ion is observed a large number of times in sequence. A single ion cannot be discussed in a pure ensemble language.

 

[martinbn]

The meaning of the state is the difference. If the state is only the description of an ensemble of independent identically prepared system, then the state is not able to describe details of an individual system that go beyond what you be true for any identically prepared system.

How is that different from any other type of measurment?

Well, an idea could be to distinguish between the state and what you want to assert about the state. Then you could let the unknown state be the description of the individual system, and determine what you can or cannot assert about it based on what you learn from your measurements.

I was asking specifically about the 2012 nobel prize work.

 

[martinbn]

I had said it several times: The fact that only a single ion is observed a large number of times in sequence. A single ion cannot be discussed in a pure ensemble language.

So, you are saying that the statistical interpretation cannot discuss repeated measearments? I disagree.

 

[A. Neumaier]

So, you are saying that the statistical interpretation cannot discuss repeated measurements? I disagree.

No. The statistical interpretation cannot discuss measurements on only a single atom - the same in all measurements. Of course it can discuss repeated measurements on a large ensemble of atoms.

 

[martinbn]

No. The statistical interpretation cannot discuss measurements on only a single atom - the same in all measurements. Of course it can discuss repeated measurements on a large ensemble of atoms.

That's what I meant by repeated measurments. One atom measured more than ones in succession. Say you pass it through a SG and then through another one. Why should this be impossible for the statistical interpretation to handle and why do you need anything more compliated than this, like 2012 nobel, for you to make your point?

 

[gentzen]

I was asking specifically about the 2012 nobel prize work.

The relation to the 2012 nobel prize work is the focus on individual ions or photons:

Individual ions can now be manipulated ... In another type of experiment, photons can be trapped in a cavity and manipulated ...

OK, not sure whether they really mean an individual photon (because they write "photons"), but they definitively mean an individual ion. If they repeat their experiment many times with different individual ions, then they can also use the minimal statistical interpretation, at least if they don't make assertions about the state of individual ions in their experiments.

 

[A. Neumaier]

That's what I meant by repeated measurements. One atom measured more than ones in succession. Say you pass it through a SG and then through another one. Why should this be impossible for the statistical interpretation to handle?

How do you handle it with the minimal statistical interpretation? The latter is only about ensembles, not about individuals!

If they repeat their experiment many times with different individual ions, then they can also use the minimal statistical interpretation, at least if they don't make assertions about the state of individual ions in their experiments.

But instead they repeat their measurements many times on the same ion. Thus they cannot use the minimal statistical interpretation.

 

[*now*]

A fresher foundational look at an old link from btsm might add some thoughts around the topic [gr-qc/0306059] A simple background-independent hamiltonian quantum model (arxiv.org)

 

[PeterDonis]

That's what I meant by repeated measurments. One atom measured more than ones in succession.

That's not what the statistical interpretation is talking about. It is talking about making one measurement on each of a large ensemble of identical systems prepared by the same preparation procedure. It is not talking about making many measurements on a single system which is only prepared once (and then measured many times in succession). Those are two different things and one cannot be substituted for the other.

 

[vanhees71]

They interpret a single time series as giving evidence of temporal properties of the single ion. No ensemble of ions is involved. This is the whole point of probing individual quantum systems. Being able to control and read the state of a single quantum object is the prerequisite of quantum computing.No, only that the statistical interpretation is incomplete since one cannot infer measurable physical properties of single systems without having a postulate that relates these measurable properties to the state.

No, there's no ensemble of ions involved but an ensemble of photons. You can use a single quantum system and repeat your experiment using this single quantum system a lot of times. That's simply done by using a laser field to excite one and the same ion again and again and observe the emitted photons from the deexcitation giving the pattern depicted in the Nobel paper.

The statistical meaning of quantum states is to the best of our knowledge not incomplete, because there's no hint that the described randomness is not a feature of Nature. In other words there's no hint that one needs hidden variables and determinism to describe the phenomena.

 

[A. Neumaier]

your alternative theory you called "thermal interpretation" before. Now it seems to be called "coherent quantum mechanics".

No. The latter is the name of my book. The thermal interpretation of quantum physics is discussed in Chapters 9-13. But the book contains much more!

I have had a chance to have a look at a preview on Amazon. I generally like to buy books by Mentors/Science Advisors here. IMHO it is both provocative and good. Written at a nice level that undergrads can generally understand. It is a worthwhile addition to the literature on QM foundations, and I will eventually get a copy.

Some chapters are indeed understandable on the undergraduate level. However, large parts of Chapters 4-7 (on coherent spaces, geometric quantization, quantum field theory, and coarse-graining) are more demanding and are best read with some background in functional analysis.

 

[DennisN]

For example, one puzzle for me has been of historical and sociological nature:
Why does popular science get QM so badly wrong? [...]

I'm actually interested in this puzzle also, but I don't see it as puzzling as QM itself , since I remember personally when I was more uninformed about QM. I think the counterintuitive nature of QM and the departure from classical physics are two strong contributing factors to why it's hard to summarize aspects of QM in articles. Also, we have lived with classical physics for a couple of centuries, and with QM for only about a century.

Another puzzle which I've started to find quite interesting the last couple of years is quite simply why there are so many interpretations of QM. I am not aware of any other field of science with so many different interpretations.

Is this because:

• It is counterintuitive and a departure from classical physics, which in turn stimulates interpretations?
• There are truly important unresolved issues in QM?
• QM is close to/at the frontline of our current knowledge? (which it is)
• Some (many?) believe QM is not the end of the story?
• Or a combination of all those?

I don't know. Maybe future will tell.

 

[bhobba]

Why does popular science get QM so badly wrong? How did it happen that the "consciousness causes collapse" interpretation got associated with the names of John von Neumann and Eugene Wigner? What was the role of Henry P. Stapp in this?

One answer - basic calculus. That's all you need to understand a proper book:
https://www.amazon.com.au/dp/0465062903/

But people do not want to even put in a weekend learning basic intuitive calculus.

This consciousness issue is a hangover from the early days, and very few hold to it these days. For example, many years later Wigner changed his mind to reflect a simpler and more realistic objective position. But populist accounts sell more books by being sensationalist rather than exact.

Thanks
Bill

 

[bhobba]

How do you handle it with the minimal statistical interpretation? The latter is only about ensembles, not about individuals!

Isn't this the same issue in any probabilistic prediction? We all know the frequentist interpretation has foundational issues:
https://math.ucr.edu/home/baez/bayes.html

But applied mathematicians use it all the time, like taking dx etc., as tiny changes in x.

Thanks
Bill

 

[RUTA]

Another puzzle which I've started to find quite interesting the last couple of years is quite simply why there are so many interpretations of QM. I am not aware of any other field of science with so many different interpretations.

Fuchs takes the foundations community to task on this very question in this paper:

Quantum theory as a weather-sturdy structure has been with us for 75 years now. Yet, there is a sense in which the struggle for its construction remains. I say this because one can check that not a year has gone by in the last 30 when there was not a meeting or conference devoted to some aspect of the quantum foundations. Our meeting in Vaxjo, “Quantum Theory: Reconsideration of Foundations,” is only one in a long, dysfunctional line.

But how did this come about? What is the cause of this year-after-year sacrifice to the “great mystery?” Whatever it is, it cannot be for want of a self-ordained solution: Go to any meeting, and it is like being in a holy city in great tumult. You will find all the religions with all their priests pitted in holy war—the Bohmians[3], the Consistent Historians[4], the Transactionalists[5], the Spontaneous Collapseans[6], the Einselectionists[7], the Contextual Objectivists[8], the outright Everettics [9, 10], and many more beyond that. They all declare to see the light, the ultimate light. Each tells us that if we will accept their solution as our savior, then we too will see the light.

But there has to be something wrong with this! If any of these priests had truly shown the light, there simply would not be the year-after-year conference. The verdict seems clear enough: If we— i.e., the set of people who might be reading this paper—really care about quantum foundations, then it behooves us as a community to ask why these meetings are happening and find a way to put a stop to them.

 

[bhobba]

Fuchs takes the foundations community to task on this very question in this paper:

Nice one. I know that paper, which influenced me a lot during my early days of posting here and led to my view of QM as a generalised probability theory. Here is another by John Baez in the same 'spirit.'
https://math.ucr.edu/home/baez/prob/prob.pdf

Thanks
Bill

 

[A. Neumaier]

Fuchs takes the foundations community to task on this very question in this paper:

And in spite of his paper, the sequence of conferences has continued. Clearly his stance didn't solve the problem!

 

[A. Neumaier]

Isn't this the same issue in any probabilistic prediction? We all know the frequentist interpretation has foundational issues:
https://math.ucr.edu/home/baez/bayes.html

But applied mathematicians use it all the time, like taking dx etc., as tiny changes in x.

Yes.
The difference to the point of view of @vanhees71 is that applied mathematcians don't claim that a minimal statistical interpretation solves the foundational issues. They are satisfied with the formalism together with the handwaving interpretation of probability!

 

[bhobba]

Yes.
The difference to the point of view of @vanhees71 is that applied mathematcians don't claim that a minimal statistical interpretation solves the foundational issues. They are satisfied with the formalism together with the handwaving interpretation of probability!

As a proponent of the minimal statistical interpretation, I don't believe it solves foundational issues. I believe, as Einstein did, QM is incomplete. The minimal statistical interpretation simply says - all we can predict is probabilities of observations. What is going on between observations, or exactly how is the probability determined - blank out. It is just a pragmatic view. Like me, I know Vanhees also advocates the minimal statistical interpretation, and I do not want to put words in his mouth, but I suspect he too agrees with Einstein. I know you correctly point out Einstein was not its originator, but he championed it because it is just a pragmatic view and doesn't really solve foundational issues. It gelled with his view QM was incomplete. We have to be careful here, though, because there is debate on just what the foundational issues are. I believe the 'basic' foundational issue is QM is incomplete.

Could this be one reason there is still much debate about foundations? To be specific different expectations on what an interpretation should do?

Thanks
Bill

 

[vanhees71]

Nice one. I know that paper, which influenced me a lot during my early days of posting here and led to my view of QM as a generalised probability theory. Here is another by John Baez in the same 'spirit.'
https://math.ucr.edu/home/baez/prob/prob.pdf

Thanks
Bill

Yes, and the problem with this is that it's not religious but just observing what physicists concerned with physics and not with religion doing with quantum theory as a physical theory.

I think with all the Bell tests confirming quantum theory and with all the physical substantial knowledge used in engineering now all the apparent quibbles of interpretation are obsolete. Physicists asked Nature a question about her behavior by doing precise experiments and got an answer. The really puzzling aspect of all this is that some physicists don't accept the answer and think there are still quibbles because it's counterintuitive to their world view. However, the very purpose of the natural sciences and the empirical basis of it is not to confirm anybodies worldview or religious believes but to learn how Nature behaves. With a problem settled one should accept the result and go on to the real scientific problems. There are enough within the known physics and if you like really fundamental questions there's the still unsolved problem of how to describe the gravitational interaction consistently within QT.

It may well be that QT is indeed incomplete and one needs a completely new concept to achieve this goal, but I don't think that it's incomplete, because it's indeterministic as Einstein believed. I think the lesson we've learned is that nature is at the most fundamental level not deterministic.