Quantum measurement of spins and magnets, and the classical limit of PR-boxes

Abstract

When Alice measures all her spin-$\half$ of a large ensemble of $N$ singlets, all along the same direction $\vec{a}$, she prepares at a distance an ensemble of spins for Bob which, because of statistical fluctuations, have a magnetic moment of the order $\sqrt{N}$. By making $N$ large enough, this magnetic moment can be made arbitrarily large. We show that, nevertheless, Bob can't read out of this large magnetic moment Alice's choice of measurement direction $\vec{a}$. We also consider stronger than quantum correlations and show that Tsirelson's bound follows from the physical assumption that in the macroscopic limit all measurements are compatible and that this should not lead to signaling.

Talk presented at the European Chist-Era DIQIP project meeting in May 2013. 5 pages

References in corpus (2)

• Almost quantum correlations
• Multiple Observers Can Share the Nonlocality of Half of an Entangled Pair by Using Optimal Weak Measurements

Cited by in corpus (3)

• Non-Locality Without Counterfactual Reasoning
• Weak Measurement and Two-State-Vector Formalism: Deficit of Momentum Transfer in Scattering Processes
• Study of nonlocal correlations in macroscopic measurement scenario