Tuesday, December 21, 2010

More Tests Against Realism

The Leggett inequality has been violated in another experiment.

I've mentioned this test earlier in which, even invoking non-locality, certain aspect of realism still cannot survive tests that produced results consistent with quantum mechanics. Now comes a newer test that eliminated even more classes of realism. It is published in New Journal of Physics[1], which is an open access journal and should be accessible to everyone.

Abstract: We report an experimental test of Leggett's non-local hidden variable theory in an orbital angular momentum (OAM) state space of light. We show that the correlations we observe are in conflict with Leggett's model, thus excluding a particular class of non-local hidden variable theories for the first time in a non-polarization state space. It is known that the violation of the Leggett inequality becomes stronger as more detection settings are used. The required measurements become feasible in an OAM subspace, and we demonstrate this by testing the inequality using three and four settings. We observe excellent agreement with quantum predictions and a violation of five and six standard deviations, respectively, compared to Leggett's non-local hidden variable theory.


[1] J. Romero et al., N. Jour. Phys. v.12, p.123007 (2010).


mi said...

Can you explain what you mean by "realism"? I understand realism to mean the proposition that there is a physical reality independent of our observations. This seems pretty similar to a hidden variable theory of QM, but it's not obvious to me that either one entails the other.

ZapperZ said...

That is what it is.


To me, it means that a physical system has a definite state before it is measured. Classically, a tossed coin already has an outcome before it is looked at. In QM, this is not the case, that superposition is true.


mi said...

ah, okay. Thanks for the link!