New "loophole free" EPR test with photons by Wittmann et al

Demystifier

Well, not all:
http://www.physicsforums.com/blog.php?b=3622

Demystifier

Does it mean that there is some type of LHV that COULD explain steering, but could not explain violation of Bell inequalities? If yes, what type of LHV it is?

zonde

> - Copenhagen - nature is local, but objective reality does not exist (Bohr, Mermin, Rovelli-relational, Zeilinger, ...)
"Reality does not exist" is not an explanation it's more like antithesis of explanation.

> - many worlds - objective reality exists and is "local", but not in the 3-space (Everett, Deutsch, Tegmark, ...)
Simultaneous distant reality is not uniquely determined in MWI so how can you claim it's local?

> - superdeterminism - objective reality exists, it is local and deterministic, but initial conditions are fine tuned ('t Hooft)
Generally conspiracy theories are not considered.

> - backward causation - objective reality exists and is local, but there are signals backwards in time (transactional interpretation)
You can't propose oxymoron as an explanation.

> - noncommutative hidden variables - objective reality exists and is local, but is not represented by commutative numbers (Joy Christian)
There is no correspondence between noncommutative hidden variables based explanation and physical reality.

> - solipsistic hidden variables - objective reality exists and is local, but objective reality describes only the observers, not the observed objects (H. Nikolic, http://xxx.lanl.gov/abs/1112.2034 )
From solipsistic point of view you are now arguing with yourself.

zonde

Bell's naive LHV model can violate steering inequalities.

yoda jedi

"reality" in the case, argumenting that the term reality is defined by "properties".



.

Demystifier

That seems interesting and important, but requires additional explanations.
1. What is Bell naive LHV model?
2. Where in the Bell's "Speakable ..." book is it described?
3. Is there a reference where it is explicitly shown (or at least claimed) that Bell's naive LHV model can violate steering inequalities?

Thank you in advance!

zonde

I don't have this book so if you don't mind I will use this link:
http://www.drchinese.com/David/Bell_Compact.pdf
Bell says: "..., it follows that the result of any such measurement must actually be predetermined."
and then this paragraph starting with "Let this more complete specification be effected by means of parameters λ."
Basically it says that experimental outcome is predetermined for particular angle of analyser by λ and nothing else. λ is shared between particles.
???
Bell's naive model is based on the need to provide perfect correlations for matching angles. It starts from that point. Steering inequalities consider only matching angles. What else do you need.

Besides steering inequalities appeared rather recently so it would be up to authors of these inequalities to compare them with Bell inequalities, don't you think?

BTW have you seen any free access reference for that steering?

yoda jedi

non-locality from uncertainty principle.

..Likewise, nonlocality was traditionally thought of in terms of something called a Bell inequality, which also obscured the link between nonlocality and uncertainty...

... strength of a property called "steering'', which determines which states can be prepared at one location given a measurement at another....

http://arxiv.org/abs/1004.2507

zonde

Thanks yoda jedi, but the key person seems to be Wiseman so I suppose that most relevant papers should be in these search results:
http://arxiv.org/find/quant-ph/1/AND.../0/1/0/all/0/1


Say from this paper http://arxiv.org/abs/quant-ph/0612147
"In this Letter, we address the following questions: Can all entangled states be used to demonstrate steering? Does a demonstration of steering also demonstrate Bell-nonlocality? We prove that in both cases the answer is again: no. Thus, steerability is a distinct nonlocal property of some bipartite quantum states, different from both Bell-nonlocality and nonseparability."

Seems to answer Demystifier's question.

harrylin

I'm still completely lost here... Can anyone explain in clear terms what the difference is between "Bell-nonlocality" and "nonlocal"?

Demystifier

My current understanding of it (open to further refinements), compatible with the zonde's explanations, can be summarized as follows:
Steering can be explained by local hidden variables, but it cannot be explained by local reduced density matrix alone.

zonde

I would say that "Bell-nonlocality" is correlation that can not be explained by common cause.

harrylin

As I understood all discussions until now, "nonlocal" means a correlation that can not be explained without something "spooky" such as instantaneous "action at a distance". And I think that with "Bell-nonlocality" people essentially refer to the same, but more specifically to "Bell" type of experiments and his arguments about those.

If so, then with the statement "steerability is a distinct nonlocal property", the Arxiv letter http://arxiv.org/abs/quant-ph/0612147 by Wiseman claims that steering implies "nonlocality" in the sense of EPR - so that steering is claimed to be unexplainable with "local variables".

Demystifier

Yes, that's correct.