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Classical Information and Collapse in Wigner’s Friend Setups
Version 1
: Received: 17 August 2023 / Approved: 17 August 2023 / Online: 18 August 2023 (09:48:14 CEST)
A peer-reviewed article of this Preprint also exists.
Baumann, V. Classical Information and Collapse in Wigner’s Friend Setups. Entropy 2023, 25, 1420. Baumann, V. Classical Information and Collapse in Wigner’s Friend Setups. Entropy 2023, 25, 1420.
Abstract
The famous Wigner’s friend experiment considers an observer – the friend– and a superobserver –
Wigner– who treats the friend as a quantum system and her interaction with other quantum systems as
unitary dynamics. This is at odds with the friend describing this interaction via collapse dynamics, if
she interacts with the quantum system in a way that she would consider a measurement. These different
descriptions constitute the Wigner’s friend paradox. Extended Wigner’s friend experiments combine the
original thought experiment with non-locality setups. This allows for deriving local friendliness inequalities,
similar to Bell’s theorem, which can be violated for certain extended Wigner’s friend scenarios. A Wigner’s
friend paradox and the violation of local friendliness inequalities require that no classical record exists,
which reveals the result the friend observed during her measurement. Otherwise Wigner agrees with
his friend’s description and no local friendliness inequality can be violated. In this article, I introduce
classical communication between Wigner and his friend and discuss its effects on the simple as well as
extended Wigner’s friend experiments. By controlling the properties of a (quasi) classical communication
channel between Wigner and the friend one can regulate how much outcome information about the friend’s
measurement is revealed. This gives a smooth transition between the paradoxical description and the
possibility of violating local friendliness inequalities, on the one hand, and the effectively collapsed case,
on the other hand.
Keywords
Wigner's friend; Communcation; Collapse
Subject
Physical Sciences, Quantum Science and Technology
Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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