En vidéo-conférence : 10 décembre 2020 – 10:00 https://cern.zoom.us/j/91315192376?pwd=aEJPZWxNUWQxNXdTbnprR1FHQ3J4Zz09
A strong no-go theorem on the Wigner’s friend paradox
Wigner’s friend paradox is a thought experiment illustrating the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement. In this talk I review our recent no-go theorem on the Wigner’s friend paradox , in which we prove that if quantum evolution is controllable on the scale of an observer, then one of three assumptions must be false: ‘No-Superdeterminism’, ‘Locality’ or ‘Absoluteness of Observed Events’—the last of which meaning that every observed event exists absolutely, not relatively. From these assumptions we derive inequalities for an extended version of the Wigner’s friend scenario, and show that they can be violated by quantum correlations. This is demonstrated in a proof-of-principle experiment where a photon’s path is deemed an observer. I will discuss how this new theorem places strictly stronger constraints on physical theories than Bell’s theorem, the status of current and future experimental tests, and other implications for research on the foundations of quantum mechanics.
 Bong, KW., Utreras-Alarcón, A., Ghafari, F. et al. A strong no-go theorem on the Wigner’s friend paradox. Nat. Phys. (2020). https://doi.org/10.1038/s41567-020-0990-x