English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

The Wigner's friend paradox concerns one of the most puzzling problems ofquantum mechanics: the consistent description of multiple nested observers.Recently, a variation of Wigner's gedankenexperiment, introduced by Frauchigerand Renner, has lead to new debates about the self-consistency of quantummechanics. At the core of the paradox lies the description of an observer andthe object it measures as a closed system obeying the Schr\"odinger equation.We revisit this assumption to derive a necessary condition on a quantum systemto behave as an observer. We then propose a simple single-photoninterferometric setup implementing Frauchiger and Renner's scenario, and usethe derived condition to shed a new light on the assumptions leading to theirparadox. From our description, we argue that the three apparently incompatibleproperties used to question the consistency of quantum mechanics correspond totwo logically distinct contexts: either one assumes that Wigner has fullcontrol over his friends' lab, or conversely that some parts of the labs remainunaffected by Wigner's subsequent measurements. The first context may be seenas the quantum erasure of the memory of Wigner's friend. We further show theseproperties are associated with observables which do not commute, and thereforecannot take well-defined values simultaneously. Consequently, the threecontradictory properties never hold simultaneously.

Quantum erasing the memory of Wigner's friend