Allowing Wigner’s friend to sequentially measure incompatible observables

Author:

Utreras-Alarcón Aníbal1,Cavalcanti Eric G.2ORCID,Wiseman Howard M.1ORCID

Affiliation:

1. Centre for Quantum Computation and Communication Technology (Australian Research Council Centre of Excellence), Centre for Quantum Dynamics, Griffith University, Brisbane QLD 4111, Australia

2. Centre for Quantum Dynamics, Griffith University, Gold Coast, QLD 4222, Australia

Abstract

The Wigner’s friend thought experiment has gained a resurgence of interest in recent years thanks to no-go theorems that extend it to Bell-like scenarios. One of these, by us and co-workers, showcased the contradiction that arises between quantum theory and a set of assumptions, weaker than those in Bell’s theorem, which we named ‘Local Friendliness’. Using these assumptions, it is possible to arrive at a set of inequalities for a given scenario, and, in general, some of these inequalities will be harder to violate than the Bell inequalities for the same scenario. A crucial feature of the extended Wigner’s friend scenario in our aforementioned work was the ability of a superobserver to reverse the unitary evolution that gives rise to their friend’s measurement. Here, we present a new scenario where the superobserver can interact with the friend repeatedly in a single experimental instance, either by asking them directly for their result, thus ending that instance, or by reversing their measurement and instructing them to perform a new one. We show that, in these scenarios, the Local Friendliness inequalities will always be the same as Bell inequalities.

Funder

Foundational Questions Institute

Centre of Excellence for Quantum Computation and Communication Technology, Australian Research Council

Publisher

The Royal Society

Reference18 articles.

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4. A strong no-go theorem on the Wigner’s friend paradox

5. A no-go theorem for the persistent reality of Wigner’s friend’s perception

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