A Quantum measurement of a Strontium ion

[PeterDonis]

if you force and electron into a curved trajectory it will radiate photons (e.g. synchrotron radiation)

Remember we are talking about QM. In QM, the electron will have an amplitude to radiate photons. One then has to set up the experiment to make this amplitude as small as possible during the experiment. Then one makes a large number of runs of the experiment, and one expects that during some appreciable fraction of these runs, no photon was emitted so no information is irreversibly lost.

Your apparent belief that photons are somehow immune from this is mistaken, btw. One has the issue of maintaining coherence with photons as well. Passing a photon through a beam splitter has a nonzero amplitude for the photon being absorbed in the splitter instead of passing through into the output beams. This is a nonzero amplitude for irreversible loss of information.

Due to Zeeman spin up and down states should differ in energy levels, no?

Not once they are recombined. The Zeeman effect, by itself, is unitary and reversible.

i am looking for the experimental cases where this is done for any charged or neutral particles with a magnetic moment and where the beam is split via a magnetic field (i.e. Zeeman applies)

I believe I have already said several times that I do not know of any experiments which attempt to recombine SG beams or anything equivalent.

 

[PeterDonis]

if i want to know if a particular collapse type has occurred (defined by its observable/eigenstates) i just have to do interferometry with those states and see the results

You are confusing two different meanings of "interferometry". One meaning is "putting a bunch of devices in the experiment that can produce interference", like beam splitters in an MZI. The second meaning is "putting detectors in the experiment that register irreversible results, and then using those results to infer whether interference has occurred".

The first meaning above, in itself, does not cause collapse under any interpretation. You can put a hundred beam splitters in your experiment and no collapse will happen under any interpretation just because of the beam splitters.

The second meaning above, combined with the first kind of experimental configuration, can indeed tell you whether interference has occurred; but that's not the same as telling you whether collapse has occurred inside the apparatus. You already know that collapse never occurs inside the apparatus according to any interpretation, as I said just above.

Plus, even having irreversible results recorded at the detectors doesn't tell you that collapse has occurred, because not all interpretations have collapse in them at all. According to the MWI, there is never any collapse, even when detectors register irreversible results.

 

[Killtech]

You are confusing two different meanings of "interferometry". One meaning is "putting a bunch of devices in the experiment that can produce interference", like beam splitters in an MZI. The second meaning is "putting detectors in the experiment that register irreversible results, and then using those results to infer whether interference has occurred".

The first meaning above, in itself, does not cause collapse under any interpretation. You can put a hundred beam splitters in your experiment and no collapse will happen under any interpretation just because of the beam splitters.

The second meaning above, combined with the first kind of experimental configuration, can indeed tell you whether interference has occurred; but that's not the same as telling you whether collapse has occurred inside the apparatus. You already know that collapse never occurs inside the apparatus according to any interpretation, as I said just above.

I know quite well how interferometry is normally performed. And I work on an extension to what you called the "first meaning".

Okay, maybe exchange the word "collapse" for decoherence and I think it should be quite clear how an interferometry setup is usable to check if coherence was lost or not. A possible decoherence could collapse the superposition into a corresponding ensemble. Which means that this acts about the same as a "measurement collapse" (minus the instantaneous and now-well defined aspect) which however does not consume the particle like a detector would but allows it to travel on in the collapsed state.

Plus, even having irreversible results recorded at the detectors doesn't tell you that collapse has occurred, because not all interpretations have collapse in them at all. According to the MWI, there is never any collapse, even when detectors register irreversible results.

In my opinion, there's no collapse happening ever, but as you see on the example of this thread, this opens rather a can of worms than helping to answer this question.

So to clarify: whenever I talk about a collapse I always mean an objective event which can be experimentally verified in principle and never about the "interpretation" thing. It just so happens that these two quite often overlap in an extended framework whenever the prior gains the capacity to describe physics that are part of the measurement process.

In a more general context I was trying to understand what impact full QED time evolution might have for various states. In terms of decoherence QED takes away the idea of an isolated system as any particle now always interacts with the other fields around it. And with simple proxy calculation I made it seems that any system composed of anything electrically charged, every superposition of states with different energy levels will swiftly lose their energy to the EM-field and thus decay into pure states and where on the other hand energy eigenstates would seem stable. Ironically enough this works just along the lines of the instability in Bohrs old atom model from Larmor frequency. Or in other words: the system undergoes a reversed Rabi oscillation - reversed because it becomes itself the source of the oscillatory field to which it loses energy. Well, okay a superposition becomes stable if the right oscillatory field is applied externally. And interestingly trying to spatially separate the superposition won't help but may even make things worse - that's where calculation get the most messy as it approaches a division by zero.

In any case this is why it did go against my intuition that a superposition in SG would be able to maintain coherence while it is in the magnetic field - and once lost it cannot be regained upon recombination.

 

[PeterDonis]

maybe exchange the word "collapse" for decoherence

Which makes a huge difference. Decoherence is part of the "minimal" math of QM, it is there regardless of what interpretation you choose. So testing for decoherence is interpretation independent. Testing for collapse is not.

Also, as I've already noted, testing for decoherence does not test for any kind of "collapse", whether the interpretation dependent one of standard QM or some alternative theory that is different from standard QM (see below). So "collapse" is not a good term to use if what you mean is "decoherence".

whenever I talk about a collapse I always mean an objective event which can be experimentally verified in principle and never about the "interpretation" thing

Then you are either talking about decoherence (as above), or you are talking about some different theory from standard QM, such as the GRW "spontaneous collapse" theory. In either case, just using the term "collapse" without qualification is not a good way to communicate what you are talking about. We could have avoided this whole fruitless discussion if you had been clearer about this at the outset.

I talked about testing for decoherence above. Obviously you can also test a theory that is different from standard QM by finding a situation where it makes different predictions from standard QM and then running the experiment. But first you have to decide what different theory you are talking about. Are you trying to investigate the GRW theory? Or some other theory? That is the crucial missing piece. Without a specific alternative theory there is no way to know where it will make different predictions from standard QM.

It just so happens that these two quite often overlap

No, they don't "overlap", they just can both be talked about in the context of the same experiment--but that doesn't make them the same or excuse confusing one with the other.

 

[vanhees71]

So to clarify: whenever I talk about a collapse I always mean an objective event which can be experimentally verified in principle and never about the "interpretation" thing. It just so happens that these two quite often overlap in an extended framework whenever the prior gains the capacity to describe physics that are part of the measurement process.

I've not a single example for the observation of a collapse. All measurements I know of are well describable by local interactions between measured objects and measurement devices.

 

[PeterDonis]

I've not a single example for the observation of a collapse.

It turns out he doesn't mean what we thought he meant by "collapse". See my post #124 just now.

 

[PeterDonis]

Since the OP is long gone and it turns out most of the discussion since was based on a miscommunication, this thread is now closed.