Spatial separation of entangled particles implies physical separability?

[bhobba]

So, today I’d put the question like this: which physical operation establishes the transition from an initially joint nonfactorizable structure to physical disconnection or to exhaustively independent local wholes?

The answer depends on the interpretation; for example, in Bohmian Mechanics, particles are separate in the classical sense.

In the formalism of Quantum Field Theory, two entangled particles are a single 'excitatIon' of the quantum field. If you observe it with the particle number operator, you get two. However, if you observe a single-particle property, you instantly break the entanglement and get two separate excitations, each of a single particle. In other words, they are an entangled pair until an interaction (observation) breaks the entanglement.

If this is still in relation to Einstein's famous EPR paper, be aware that it is way out of date today, to the point that some say it is nonsense. This is hardly surprising since QM has developed enormously since then.

I think you may benefit from reading Bell's writings:
https://faculty.washington.edu/seattle/physics441/interpretations/Bell.pdf

Thanks
Bill

 

[aletheia]

The answer depends on the interpretation; for example, in Bohmian Mechanics, particles are separate in the classical sense.

In the formalism of Quantum Field Theory, two entangled particles are a single 'excitatIon' of the quantum field. If you observe it with the particle number operator, you get two. However, if you observe a single-particle property, you instantly break the entanglement and get two separate excitations, each of a single particle. In other words, they are an entangled pair until an interaction (observation) breaks the entanglement.

If this is still in relation to Einstein's famous EPR paper, be aware that it is way out of date today, to the point that some say it is nonsense. This is hardly surprising since QM has developed enormously since then.

I think you may benefit from reading Bell's writings:
https://faculty.washington.edu/seattle/physics441/interpretations/Bell.pdf

Thanks
Bill

Thanks for the material — it will be very useful indeed.
Different interpretations provide different ontological accounts.
However, my question is prior to choosing among them — it’s more a logic one than a philosophic one, that is: does the experimentally established spatial separation and dynamical decoupling entail physical disconnection or exhaustive ontological independence?
Measurement interaction can destroy a specified entangled structure, but that identifies a physical process, not a derivation of exhaustive ontological independence.
Entanglement-breaking channels also provide a concrete example of a physical process that can destroy entanglement — it’s a process that can be characterized, that has its consequences and can be experimentally tested.
The logic is: with the knowledge available in 1935 (when EPR was published), before concluding that QM is incomplete on the basis of locality and separability assumptions, one must first identify precisely what those assumptions establish about the physical systems.
And if a proposed explanation requires an initially joint physical structure to have been lost and somehow restored, one must first identify the physical process responsible for that loss.
Clearly, EPR's t = T stipulation, by itself, does not entail ontological disconnection.
My logic audit is between what an interpretation postulates and what the observations and formalism necessarily entail.

 

[Matterwave]

If this is still in relation to Einstein's famous EPR paper, be aware that it is way out of date today, to the point that some say it is nonsense. This is hardly surprising since QM has developed enormously since then.

I don't think the age of the argument makes it outdated or nonsense. They missed an implicit assumption of locality which was later pointed out by Bell and their final point using counterfactuals to attack the uncertainty principle wasn't really necessary, but overall it's a wonderful paper to read.

I think you may benefit from reading Bell's writings:
https://faculty.washington.edu/seattle/physics441/interpretations/Bell.pdf

Bell's original paper is titled "On the Einstein Podolsky Rosen Paradox". To understand that paper it is best to read the EPR paper to see where Bell was coming from.

 

[aletheia]

I don't think the age of the argument makes it outdated or nonsense.

Agreed. That’s why I prefer to logic audit based on what was known at that time the publication was made.

They missed an implicit assumption of locality which was later pointed out by Bell and their final point using counterfactuals to attack the uncertainty principle wasn't really necessary, but overall it's a wonderful paper to read.

Also agreed.

Bell's original paper is titled "On the Einstein Podolsky Rosen Paradox".

This one I have read.

To understand that paper it is best to read the EPR paper to see where Bell was coming from.

But there is useful material on that source.

 

[flippiefanus]

So, today I’d put the question like this: which physical operation establishes the transition from an initially joint nonfactorizable structure to physical disconnection or to exhaustively independent local wholes?

If I can translate the question into the language that I would understand, it would read: is there a physical process that can unentangle two entangled subsystems? That would be an interesting question, but I think the short answer is no.

First, let me just say that I do not understand all the terminology that is used. Perhaps these terms come from philosophy where terms like this are often debated and linked to deeper meanings. In physics and mathematics, terms are generally given precise mathematical meanings that can always be related back to their mathematical meaning from within any physical context where they are relevant.

Unfortunately, ontology is not something that the scientific method gives us much clarity about. There are numerous interpretations that try to link that which is revealed by the scientific approach to some physical reality, but none of those can be ruled out by science.

Back to the question. There is a process of decoherence that effectively removes the entanglement of subsystems, but it is not the same as what one would have if two subsystem were not entangled in the first place. To understand that, one must understand the concept of a pure state compared to a mixed state. A pure state is an exact representation of the state of a system without any ignorance. A mixed state provides an ensemble of different possible pure states with probabilities for each. When we have an entangled state given as a pure state and we ignore one of the entangled subsystems, we can trace out that subsystem, which then leads to a mixed state of the remaining subsystems, which may be un-entangled. The price we pay is the mixed nature of the result. The situation can become very complicated with multiple subsystem, some of which are ignored (unobserved) and others which are observed.

Theoretically, if we have a unitary process that converts a separable tensor product of subsystems (a pure state) into an entangled pure state, then the adjoint of that unitary process can convert the entangled state back into the original separable pure state again. Such a process can be implemented in a fully controlled environment, as for example in a quantum computer. However, in most physical scenarios, I think it would be difficult to perform such a process, especially when the two subsystems have been separated to propagate as non-interacting particles.

Hope this discussion answers at least some part of your question.

 

[PeterDonis]

Different interpretations provide different ontological accounts.
However, my question is prior to choosing among them

It doesn't seem like it to me. See below.

it’s more a logic one than a philosophic one, that is: does the experimentally established spatial separation and dynamical decoupling entail physical disconnection or exhaustive ontological independence?

This looks like a classic interpretation question. "Exhaustive ontological independence" is not something you'll find anywhere in the math of QM. It's the sort of claim a particular interpretation might make. You're not asking how QM makes accurate predictions using precise math. You're asking what kind of story you should be telling in vague ordinary language. That's interpretation.

Measurement interaction can destroy a specified entangled structure

Only in an interpretation where collapse is an actual physical process. In the MWI, for example, entanglement is never destroyed; it just gets spread into the measuring apparatus as well as the measured system.

 

[PeterDonis]

Moderator's note: Based on the subject matter, this thread has been moved to the QM interpretations subforum.