Classical multi-party signalling violates predefined causal order maximally
Wednesday, 04 Jun. 2014, 15:00 - 17:00
Presenter: Ämin Baumeler
Host: Caslav Brukner
Where: IQOQI Seminar Room, 2nd Floor, Boltzmanngasse 3, 1090 Vienna
Aspects of general relativity and quantum theory are combined in a recent framework of Oreshkov, Costa, and Brukner (2012). The authors drop the assumption of a global background time, while keeping the validity of ordinary quantum theory in local laboratories, and show that the resulting framework relaxes quantum theory to dynamical causal structures; their framework allows for quantum correlations incompatible with any predefined causal order, i.e., correlations that are not causal realistic. Interestingly, in the macroscopic (classical) limit of the two-party setting, a predefined causal order always emerges. This suggests that also in the setting with any number of parties, a predefined causal order might be the result of a quantum-to-classical transition. Counter to this belief, we show that deterministic macroscopic correlations among three parties or more incompatible with any predefined causal order are possible [arXiv:1403.7333 [quant-ph] (2014)], i.e., the framework constructed by dropping the assumption of a global background time, while assuming that local laboratories are described by classical probability theory, allows for correlations that are not causal realistic.