Frontiers of quantum physics

Abstract:

In this paper I discuss the question: what comes first, physics or information? The two have had a long-standing, symbiotic relationship for almost a hundred years out of which we have learnt a great deal. Information theory has enriched our interpretations of quantum physics, and, at the same time, offered us deep insights into general relativity through the study of black hole thermodynamics. Whatever the outcome of this debate, I argue that physicists will be able to benefit from continuing to explore connections between the two. © 2012 by the authors; licensee MDPI, Basel, Switzerland.

Abstract:

We show that a pair of massive relativistic spin-1/2 particles prepared in a maximally entangled spin state in general is not capable of maximally violating the Clauser-Horne-Shimony-Holt (CHSH) version of Bell's inequalities without a postselection of the particles' momenta, representing a major difference in relation to nonrelativistic systems. This occurs because the quantization axis of the measurements performed on each particle depends on the particle velocity, such that it is not possible to define a reduced density matrix for the particles' spin. We also show that the amount of violation of the CHSH inequality depends on the reference frame and that in some frames the inequality may not be violated. © 2012 American Physical Society.