The Classical Channel

1:08 AM

@vzn wikipedia says "quantum trajectory theory" is a way to simulate open system dynamics. As such, it doesn't extend anything, it's just a technique to work out predictions within the standard QM formalism

Quantum Trajectory Theory

Quantum Trajectory Theory (QTT) is a formulation of quantum mechanics used for simulating open quantum systems, quantum dissipation and single quantum systems. It was developed by Howard Carmichael in the early 1990s around the same time as the similar formulation, known as the quantum jump method or Monte Carlo wave function (MCWF) method, developed by Dalibard, Castin and Mølmer. Other contemporaneous works on wave-function-based Monte Carlo approaches to open quantum systems include those of Dum, Zoller and Ritsch, and Hegerfeldt and Wilser.QTT is compatible with the standard formulation of...

vzn

3:47 AM

@glS yes quantum trajectory theory has a long history, decades long, am reading about it myself. the quanta article has some key observations that people are missing. this is helpful in some way, am now thinking maybe should pull these out into my blog.

am now thinking that maybe Minev et al have not made their points too clear. they have the basic outline but maybe its not surprising there is confusion on the results/ claims.

The Quantum Theory That Peels Away the Mystery of Measurement / quanta

> Quantum trajectory theory makes predictions that are impossible to make with the standard formulation. ---Devoret

> The excellent agreement between the predictions of QTT and the experimental results suggests something deeper than the mere fact that the theory works for single quantum systems. It means that the highly abstract “quantum trajectory” that the theory refers to (a term coined in the 1990s by physicist Howard Carmichael, a coauthor of the Yale paper) is a meaningful entity — in Minev’s words, it “can be ascribed a degree of reality.”
> This contrasts with the common view when QTT was first introduced, which held that it was just a mathematical tool with no clear physical significance.

now, need to go thru Minevs paper/ thesis carefully to understand this better, but basically they seem to be claiming QTT made a prediction about the experimental outcome that fundamentally cant be made by "standard" QM. this is mentioned/ expanded in several other refs citing Minev that have turned up from google citation analysis, also in my blog. in other words QTT started out as a calculational system but has now evolved to the point it can make a novel prediction outside of QM.

this a point made in my blog: they are not claiming a contradiction with QM, only a new prediction/ experimental measurement outside of it. in other words, its experimental proof that QM is incomplete. QTT is highly aligned with QM for almost all (past) scenarios, and it takes an extremely sophisticated/ careful setup to get to a scenario where QM makes no prediction but QTT does. the scenario involves measuring collapse in a single qubit system. it was only realizable last few yrs.

the novel prediction involves timespans associated with collapse which is instantaneous+random in the QM model, but has a defined, measurable, nonrandom time interval in QTT.

More Anonymous

7:19 AM

@glS

0

A: Is the recent Nature paper by Minev et al. evidence of new physics?

So the following has been taken from the comment section of Not Even Wrong. If you want to avoid the tricky question “What is a measurement?”, just consider an electron orbiting a nucleus, jumping to a lower energy state. Einstein asked what caused the jump. Bohr said it was probabilistic. So th...

@vzn

glS

9:55 AM

@MoreAnonymous thanks, but to be honest I don't quite see the relation with the statements you quote and the paper. That sounds like just a typical generic statement about measurements and collapse in QM

@vzn "* they are not claiming a contradiction with QM, only a new prediction/ experimental measurement outside of it*" I find that *very* hard to believe. That would still be a claim of experimental evidence of new physics, published in Nature. That would be huge, and stated way more clearly in the abstract and paper. And would be shouted from the rooftops within the scientific community itself, not just on quanta articles or youtube.
At the very least, people in the quantum community on twitter would be talking about it, which I haven't seen anyone do

regardless, the wording in the paper really isn't one of someone claiming new physics imho

More Anonymous

10:14 AM

@glS it was mainly to explain what a quantum jump is. Note in the blog goes on about why the measuring apparatus can be described by a density matrix. I kind of share the same confusion as u.

That they are making deterministic claim of the measurement why not claim it.

vzn

4:27 PM

@glS we have to look at the claims very carefully. it cant be understood with facile/ superficial analysis. how people react to the paper is secondary circumstantial evidence. speaking of "reaction," Lumo has trashed it on his blog with vulgar language. Nature is a top scientific journal with highest standards of peer review. the abstract is clear in claiming a challenge to copenhagen interpretation. there actually has been huge response on the internet to this single experiment.

how many people can understand all the details? analogy: it was said when SR was introduced by einstein only a few people in the world could understand it...

More Anonymous

5:20 PM

@vzn Acuriousmind has an answer which is not superficial. In light of that I shall be deleting my answer :P ... It's not the quantum jump we were thinking of :/

4

A: Is the recent Nature paper by Minev et al. evidence of new physics?

The trick here in "observing a quantum jump" is that this is not equivalent to doing a strong measurement that "collapses" the wavefunction. The archetypal quantum jump is a two level system with a ground state $\lvert G\rangle$ ("Ground")and an excited state $\lvert D\rangle$ ("Dark") (I'm namin...

Mithrandir24601

5:37 PM

A few years back, I did a review of weak measurements for my MSc

Essentially, weak measurements are totally valid physics

But way too many physicists describe them using, shall we say, more ambiguous terminology

Any time you've 'weakly measured' anything, all you've done is build up what the average looks like over many many iterations, given some pre-determined input state and some other postselected output state

The bits that can be made more misleading are dropping the 'over many many iterations' or 'postselected' bits

To give a very obviously misleading example - Alice and Bob are spatially separated and I can perform a weak measurement that indicates information travelling faster than light

... It's only doing so because you're postselecting

vzn

7:36 PM

@MoreAnonymous am glad ACM is engaged with this in a way that is better than some other "experts" and he endorses the experimental flair/ finesse. it is deep"er" but still only in some ways scratching the surface if you ask me. we are looking at an iceberg. 9/10 of it is underwater. it will take days, weeks, months, years for the jury to come in on this, in a sense. in another sense, the jury has already announced a verdict, but the judge/ public do not accept it. have found more related info...

@Mithrandir24601 hi would like to try to analyze this more in terms of weak vs strong measurements as introduced by ACM, the original paper doesnt seem to use all the same terms, eg tomography etc, as mentioned in my blog, there is a profusion in terms right now and it reminds me of kuhnian "incommensurability" concept (reviewing that too). but think its only part of the story!

am finding its somethiing of a deep rabbit hole in the Carrollian sense. but ofc QM has always been that way!

this physicsforums thread has been very interesting to follow, am only 1 page into it, and some very good refs/ analysis has turned up (along with more bogus/ facile/ superficial etc stuff) physicsforums.com/threads/… ... Neumaier has engaged with it seriously.

the forum thread cites this great survey paper to understand QTT more in general, but note this ref is now almost exactly 2 decades old! A simple model of quantum trajectories/ Brun arxiv.org/abs/quant-ph/0108132 (aug 2001)

it has been helpful for me in trying to understand larger background of QTT etc. think it has some very significant references.

basically there are several threads in QTT and one of them is aligned with alternative theories. quoting from Brun p31:

> The second approach is to modify quantum mechanics to get rid of the unwanted macroscopic superpositions, while retaining the usual quantum results on small scales. Theories of this nature have been proposed by Pearle[10], by Ghirardi, Rimini and Weber[11], by Di´osi[6], by Gisin[5] and Percival[12], and by Penrose[13], among others; these theories are commonly called “collapse models.”

have not looked into GRW much but think ran across it mentioned recently.

Ghirardi–Rimini–Weber theory

The Ghirardi–Rimini–Weber theory (GRW) is a spontaneous collapse theory in quantum mechanics, proposed in 1986 by Giancarlo Ghirardi, Alberto Rimini, and Tullio Weber. == Measurement problem and spontaneous collapses == Quantum mechanics has two fundamentally different dynamical principles: the linear and deterministic Schrödinger equation, and the nonlinear and stochastic wave packet reduction postulate. The orthodox interpretation, or Copenhagen interpretation of quantum mechanics, posits a wave function collapse every time an observer performs measurement. One thus faces the problem of defining...

↑ after reading this, it sounds a LOT like what minev is talking about, dont know if his team is aware of it. (still need to read minev more carefully!) ... but look at this!

> Two new parameters are introduced by the GRW theory, namely the collapse rate lambda and the localization distance r_C. These are phenomenological parameters, whose values are not fixed by any principle and should be understood as new constants of Nature. Comparison of the model's predictions with experimental data permits bounding of the values of the parameters (see CSL model).
> The collapse rate should be such that microscopic object are almost never localized, thus effectively recovering standard quantum mechanics.

crazy idea what if minev can (re?)cast his experimental results in terms of lambda & r_C !?!

now lets quote ACM physics.stackexchange.com/a/610331/33566

> If you look into the actual formulae, you will find that the evolution of the state in this period is directly dependent on the frequency of the Rabi drive ΩBD, so please do not get the impression that this specific behaviour during a "quantum jump" is universal - it is specific to the experimental setup and chosen method of observation.

↑ but this is exactly what is at stake, and which neither ACM or the (single case) experimenters can really know exactly yet, and ACMs assertion is not really in line with the experimenters ideas/ claims. ie in challenging copenhagen interpretation they are nearly explicitly claiming universality!

Mithrandir24601

8:12 PM

Have to admit, the Copenhagen interpretation is messed up. To paraphrase Sandu Popescu, if you've got multiple seemingly equally valid interpretations of a thing, that suggests that arguing over which is right is a waste of time because physics has never before given us anything fundamental with multiple equally valid interpretations, so we're missing something physical, not philosophical

vzn

@Mithrandir24601 that is exactly my position outlined recently in chat lately. eg semiclassical has been talking about philosophy vs physics. as long as the debate remains theoretical, its philosophy + interpretations, but as soon as its testable, its no longer philosophy + interpretations. that day has come

Mithrandir24601

@vzn Nah, all these interpretations still give the same result

vzn

@Mithrandir24601 are you reading me? GRW has testable parameters. it looks like minev has now tested them.

Mithrandir24601

Copenhagen is messed up, because it doesn't include modern e.g. decoherence theory

vzn

@Mithrandir24601 leading authorities in the field already highly question copenhagen but there is still not an experimental test to "invalidate it," until now.

Mithrandir24601

8:17 PM

@vzn Then it's a theory, not an interpretation

vzn

@Mithrandir24601 any theory that refers to testable "elements of reality" that are not in QM shows that the copenhagen interpretation of QM is invalid. copenhagen interpretation is, roughly, "there are not other elements of reality than what is in this theory." ie incomplete

ie we come to poppers concept of falsifiability but not exactly.

minev + GRW are not falsifying QM, they are revising/ extending it

Mithrandir24601

@vzn Eh, that's a bit much. Copenhagen is certainly valid at the correct scales. That's just how physics works, we don't say classical physics is invalid because of quantum physics, we say that quantum physics has to reduce to classical physics in the classical limit

vzn

@Mithrandir24601 copenhagen and QM formalism are not the same thing.

Mithrandir24601

But pilot wave theory is equally as valid as Copenhagen at the same scale, because they're interpretations

vzn

copenhagen interpretation is an interpretation of QM formalism that asserts the formalism captures all ("measurable"!) phenomena.

minev has made a measurement ("of elements of reality/ phenomenon") that standard QM cant explain. it has nothing to say, its undefined in the standard formulation.

Mithrandir24601

8:26 PM

@vzn Noooooooooo

vzn

lol!

Mithrandir24601

Weak measurements are part of standard quantum theory

I repeat: There is nothing weird or unusual about them

vzn

look admit am not an expert but its apparently not exactly a weak vs strong measurement. its similar

to be meaningful those terms must have technical definitions. what is their exact mathematics? GRW theory does not exactly spec. reference weak vs strong measurement, yet its a new theory

Mithrandir24601

@vzn To be more specific, in the paper they explicitly refer to e.g. "one infers that a quantum jump from |G〉to |D〉has occurred" - this has already used misleading terminology from the likes of weak measurements

vzn

will try to dig up the ref, but one person/ ref suggested that these experiments are a bit like einsteins photon in a box gedanken now realized nearly 1C later!

@Mithrandir24601 pointed this out in my blog, hope youll take a look. the language is slippery when new phenomena is found, communication is a big part of the challenge vzn1.wordpress.com/2021/01/24/subquantum-revolution-begins-now

quoting brun (2 decade old) writing again p31, maybe this is key to our present situation:

Mithrandir24601

8:37 PM

@vzn No, this isn't slippery language. How do you 'infer' that something is in a certain quantum state? Have you projected onto that state (making a measurement, causing the jump) or not (meaning you can't be sure)?

vzn

> Because these theories are not equivalent to standard quantum mechanics, in principle they can be distinguished experimentally. Unfortunately, most such theories require experimental sensitivities well beyond current technology, though Percival[12][26] has made interesting proposals of possible near-term tests

so, would you say 2 decades is "near term," or not?

@Mithrandir24601 show me the precise definition of weak vs strong measurement. GRW theory does not reject either one, its compatible with them. have you ever read any GRW theory? youre more an experimentalist right? its actually pro-experimentalism/ experimentalist one might say! :)

@Mithrandir24601 the "inference" was based on "measurement" but of a "measurement" that standard QM cant describe. its utterly speechless one might say :P

Mithrandir24601

@vzn Oh no, that's absolutely not an argument

In QM, measurements come in many many forms

vzn

@Mithrandir24601 are you familiar with the term incomplete wrt theories?

Mithrandir24601

If you can physically do it, how on earth can you not describe it?

vzn

@Mithrandir24601 a newtonian could not measure SR, so to speak.

Mithrandir24601

8:43 PM

Are you talking about the paper, or the GRW theory?

@vzn Uhhh, yeah, they absolutely could

They'd find the measurement disagrees with what they'd expect

vzn

these are some kuhnian like ideas from the founders of QM who experienced/ caused a paradigm shift themselves. have you heard of them?

> It is the Theory Which Decides What We Can Observe ---Einstein

Mithrandir24601

They couldn't reach the required speeds or anything, but that doesn't mean it's not measurable

vzn

> A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather its opponents eventually die, and a new generation grows up that is familiar with it. –PLANCK

Mithrandir24601

@vzn Yeah, now you're throwing random quotes at me

vzn

@Mithrandir24601 dont know whether youre reading any of it

Mithrandir24601

8:46 PM

@vzn I'm reading it, saying the paper is fine but it's not giving any 'new' physics

Apart from experimental methods

vzn

@Mithrandir24601 have you heard of GRW? is it new physics or not?

Mithrandir24601

@vzn It's 35 years old. Not 'new' in my book

vzn

@Mithrandir24601 its unproven. its a hypothetical theory. out of range of experimental testing for decades, just like measuring the bending of mercury light around the sun. you think someone from the dark ages could have done it? wrt GRW, the right experiment could make it a reality. right?

Mithrandir24601

@vzn No reason why not. But I'm talking about that paper about quantum jumps which has nothing to do with GRW

vzn

@Mithrandir24601 maybe you didnt read carefully, it seems to be highly aligned with GRW. maybe the authors are not aware of it. maybe theyre more "experimentalists," lol

you say copenhagen is "messed up," and here are experimenters that say they can prove it wrong, and you say, "nothing new to see here."

Mithrandir24601

8:53 PM

@vzn Or maybe I did read it carefully

Where did they say they prove Copenhagen wrong????

vzn

sigh

Mithrandir24601

> explicitly show that all jump evolutions follow anessentially identical, predetermined path in Hilbert space

This is standard unitary evolution

vzn

uh, ok, think/ concede you have some point here. no direct ref to "copenhagen." ah, very slippery :( arxiv.org/pdf/1803.00545.pdf

they dont cite heisenberg a single time either. yeah these guys really are experimentalists if they dont even cite any non-experiment papers even by the founders of QM... but this is an allusion to the copenhagen interpretation in the abstract, "reading between the lines..."

> The times at which the discontinuous jump transitions occur are reputed to be fundamentally unpredictable. Can there be, despite the indeterminism of quantum physics, a possibility to know if a quantum jump is about to occur or not?

they cite shroedinger 1952 "are there quantum jumps?" which is Schroedingers extended/ pointed diatribe against Copenhagen interpretation... alas there is not an available electronic version of this paper to see if he mentions Copenhagen directly. heres an original copy for $1450 manhattanrarebooks.com/pages/books/1398/erwin-schrodinger/…

Thomas Klimpel

11:16 PM

Of course there are electronic versions of Schrödinger's two part paper available:
https://www.informationphilosopher.com/solutions/scientists/schrodinger/Quantum_Jumps_I.pdf
https://www.informationphilosopher.com/solutions/scientists/schrodinger/Quantum_Jumps_II.pdf

And I don't think that it is an explicit diatribe against Copenhagen. It is more the suggestion that quantum physics is too important to remain a subject for specialists only:

Along with this disregard for historical linkage there is a tendency to forget that all science is bound up with human culture in general, and that scientific findings, even those which at the moment appear the most advanced and esoteric and difficult to grasp, are meaningless outside their cultural context.

A theoretical science, unaware that those of its constructs considered relevant and momentous are destined eventually to be framed in concepts and words that have a grip on the educated community and become part and parcel of the general world picture – a theoretical science, I say, where this is forgotten,

and where the initiated continue musing to each other in terms that are, at best, understood by a small group of close fellow travellers, will necessarily be cut off from the rest of cultural mankind; in the long run it is bound to atrophy and ossify, however virulently esoteric chat may continue within its joyfully isolated groups of experts.

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The Classical Channel