All tight multipartite Bell correlation inequalities for three dichotomic observables per observer

A derivation of the full set of Bell inequalities involving correlation functions, for two parties, with binary observables, and three possible local settings. The procedure can be extended straightforwardly to multiparty correlations.Comment: 10 pages, RevTe

Bell's theorem tells us NOT what quantum mechanics IS, but what quantum mechanics IS NOT

Non-locality, or quantum-non-locality, are buzzwords in the community of quantum foundation and information scientists, which purportedly describe the implications of Bell's theorem. When such phrases are treated seriously, that is it is claimed that Bell's theorem reveals non-locality as an inherent trait of the quantum description of the micro-world, this leads to logical contradictions, which will be discussed here. In fact, Bell's theorem, understood as violation of Bell inequalities by quantum predictions, is consistent with Bohr's notion of complementarity. Thus, if it points to anything, then it is rather the significance of the principle of Bohr, but even this is not a clear implication. Non-locality is a necessary consequence of Bell's theorem only if we reject complementarity by adopting some form of realism, be it additional hidden variables, additional hidden causes, etc., or counterfactual definiteness. The essay contains two largely independent parts. The first one is addressed to any reader interested in the topic. The second, discussing the notion of local causality, is addressed to people working in the field.Comment: As essay, based on my talk at the conference "Quantum [Un]Speakables II: 50 Years of Bell's Theorem" (University of Vienna, June, 2014), submitted to the proceedings of the meetin

On the Paradoxical Book of Bell

This is an essay-review on a recently re-issued book of John Bell "Speakable and Unspeakable in Quantum Mechanics". The discussion concentrates around the Bell Theorem, its assumptions, consequences and frequent overinterpretations.Comment: Replacement. The critical missing NOT is put into footnote 1. Note that in the published version NOT is still missin

Temporal Leggett-Garg-Bell inequalities for sequential multi-time actions in quantum information processing, and a re-definition of Macroscopic Realism

The usual formulation of Macrorealism is recast to make this notion fully concurrent with the basic ideas behind classical physics. The assumption of non-invasiveness of measurements is dropped. Instead, it is assumed that the current state of the system defines full initial conditions for its subsequent evolution. An example of a new family of temporal Bell inequalities is derived which can be applied to processes in which the state of the system undergoes arbitrarily many transformations (which was not the case in the original approach). An exponential (in terms of number of operations) violation of this inequality is demonstrated theoretically. Finally it is shown that such inequalities were indirectly tested in a 2005 experiment by the Weinfurter group.Comment: 5 page

Violations of Local Realism in the Innsbruck GHZ Experiment

It is shown that a careful analysis of the `wrong' events (those not present in the usual formulations of the GHZ argument), which are a necessary feature of the tests of local realism involving independent sources, permits one to show that there is no local realistic model, which is capable to describe recent GHZ experiments performed in InnsbruckComment: 1 eps figure, 4 page

Critical visibility for N-particle Greenberger-Horne-Zeilinger correlations to violate local realism

A sequence of Bell inequalities for N-particle systems, which involve three settings of each of the local measuring apparatuses, is derived. For Greenberger-Horne-Zeilinger states, quantum mechanics violates these inequalities by factors exponentially growing with N. The threshold visibilities of the multiparticle sinusoidal interference fringes, for which local realistic theories are ruled out, decrease as (2/3)^N.Comment: 8 pages, LaTe

Analysis of critical parameters in the scheme of Bj\"ork, Jonsson, and S\'anchez-Soto

Bj\"ork, Jonsson, and S\'anchez-Soto describe an interesting (gedanken-)experiment which demonstrates that single photons can indeed lead to effects which have no local realistic description. %It is one of few cases where the experimental falsification of the conjecture of local realism has been done with use of the CH inequality, rather that the CHSH inequality. We study the critical values of parameters of some possible features of a non-perfect realisation of the experiment (especially photon loss, which could be looked at as the detection efficiency), that need to be satisfied so that the experiment can be considered as a valid test of quantum mechanics versus local realism. Interestingly, the scheme turns out to be robust against photon loss.Comment: 7 pages, 3 figure

Faster than light Bell telephone of Michalski transmits only noise

Motivated by pedagogical reasons we pinpoint the mistake in the recent claim, in quant-ph/9911016, that faster than light communication is possible.Comment: RevTex, 1 pag

Entanglement swapping with PDC sources

We show that the possibility of distinguishing between single and two photon detection events is not a necessary requirement for the proof that recent operational realization of entanglement swapping cannot find a local realistic description. We propose a simple modification of the experiment, which gives a richer set of interesting phenomena.Comment: RevTex, 5 pages, 1 figur

Quantum non-locality - It ain't necessarily so...

Bell's theorem is 50 years old. Still there is a controversy about its implications. Much of it has its roots in confusion regarding the premises from which the theorem can be derived. Some claim that a derivation of Bell's inequalities requires just locality assumption, and nothing more. Violations of the inequalities are then interpreted as ``nonlocality'' or ``quantum nonlocality''. We show that such claims are unfounded and that every derivation of Bell's inequalities requires a premise -- in addition to locality and freedom of choice -- which is either assumed tacitly, or unconsciously, or is embedded in a single compound condition (like Bell's ``local causality''). The premise is equivalent to the assumption of existence of additional variables which do not appear in the quantum formalism (in form of determinism, or joint probability for outcomes of all conceivable measurements, or ``additional causes`'', or ``hidden variables'', ``complete description of the state'' or counterfactual definiteness, etc.). A certain irony is that perhaps the main message of violation of Bell's inequalities is that our notion of locality should be based on an operationally well-defined no-signalling condition, rather than on local causality.Comment: approximately the published versio