Experiments with quantum cause and effect reveal hidden nonclassicality

/physicsworld.com/ ^ | 26 May 2022 | Jessica Tucker

[BenLurkin]

Bell’s theorem states that no theory that incorporates local “hidden” variables can ever reproduce the correlations between measurement outcomes that quantum mechanics predicts. A similar result occurs in the theory of causal inference, where quantum systems likewise defy the rules of classical causal reasoning. The idea behind the causal inference approach is that while a statistical correlation between two variables can arise due to a direct causal relationship between them, the correlation may also contain the contribution of a hidden common cause.

[T]he researchers use a causal model (see image) in which the statistics of variable A influence those of variable B, either directly or by the action of a common source (called Λ) that connects the outcome of both variables even without the presence of a causal link between them. To distinguish between these two scenarios, the researchers perform an intervention on variable A that erases any external influences. This leaves the variable A under the experimenter’s complete control, making it possible to estimate the direct causal link between A and B.

Alternatively, by introducing an additional variable X that is independent of B and Λ, any observed correlations between variables A and B can be decomposed into conditional probabilities. These conditional probabilities place a lower bound on the degree of causal effect between the variables, making it possible to estimate the level of influence between A and B.

The researchers call this lower bound an instrumental inequality, and it is a classical constraint that (similar to the inequality that arises from Bell’s theorem) stems from imposing this causal structure on an experiment. As a result, the degree of quantum causal influence between variables A and B will be less than the minimum required for a classical system, allowing nonclassicality to be observed... even when no Bell inequality violated.

[Track9]

Does typical stochastic modeling account for quantum behaviors?

[MHGinTN]

Quantum kids are an unruly bunch dontchaknow.

[Track9]

Yes, they don’t like early bedtimes and never wash the dishes.

[SuperLuminal]

One reason I retired in1985 was that it appeared to me that physics (particularly theoretical physics) was becoming what we now might call “woke” (”beauty” was taking hold)...

I like this paper (yet, hoping the communist Pope wasn’t involved)...

However, relative to the reawakening of those dreaded “hidden variables”, I’d have to ask whether there’s a philosophical connection to Hillary’s memory losses or her funding of the Russia scandal...

I know...I know...
Just the ramblings of an 88-year old Freeper...