A glance beyond the quantum model

Abstract

One of the most important problems in physics is to reconcile quantum mechanics with general relativity, and some authors have suggested that this may be realized at the expense of having to drop the quantum formalism in favour of a more general theory. Here, we propose a mechanism to make general claims on the microscopic structure of the Universe by postulating that any post-quantum theory should recover classical physics in the macroscopic limit. We use this mechanism to bound the strength of correlations between distant observers in any physical theory. Although several quantum limits are recovered, such as the set of two-point quantum correlators, our results suggest that there exist plausible microscopic theories of Nature that predict correlations impossible to reproduce in any quantum mechanical system.

Quantum Measurement of Spins and Magnets, and the Classical Limit of PR-Boxes

“…Indeed, the existence of a global probability distribution excludes violation of a Bell inequality, hence guarantees the existence of a local model [12]. This also establishes the connection with the concept of macroscopic-locality [1].…”

“…This is true as well for quantum systems as for systems described by any post-quantum theory. In section III we illustrated this for large ensembles of spin- 1 2 and showed that indeed, the quantum formalism of weak measurement provides the tool to describe collective measurements and how they carefully are just at the border of not violating the no-signaling principle. In the following section we considered noisy PR-boxes, that is hypothetical boxes with stronger than quantum correlations.…”

“…Following Miguel Navascues [1] and Daniel Rochlich [2], we argue that any physical box, when there are large ensemble of them, should admit "classical" measurements. We show that isotropic noisy PR-boxes [3] satisfy this highly plausible physical constrain if and only if the noise is large enough for the correlation to be quantum.…”

Exclusivity principle forbids sets of correlations larger than the quantum set

“…While previous principles cannot rule out the existence of sets of correlations strictly larger than the quantum one for any single experiment [6][7][8][9][10][11][12][13][14], we have shown that, for self-complementary graphs, the E principle, by itself, excludes any set of correlations strictly larger than the quantum set.…”

“…One consists of reconstructing QT as a purely operational probabilistic theory that follows from some sets of axioms [1][2][3][4][5]. A second approach consists of identifying principles that explain the set of quantum nonlocal correlations [6][7][8][9][10][11][12][13][14]. The third approach consists of identifying principles that explain the set of quantum contextual correlations [15][16][17][18][19] without restrictions imposed by a specific experimental scenario [20][21][22][23].…”