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Wigner-friend scenarios -- in which external agents describe a closed laboratory containing a friend making a measurement -- highlight the difficulties inherent to quantum theory when accounting for measurements. In non-relativistic…

Quantum Physics · Physics 2024-09-13 J. Allam , A. Matzkin

The description of Wigner-friend scenarios -- in which external agents describe a closed laboratory containing a friend making a measurement -- remains problematic due to the ambiguous nature of quantum measurements. One option is to…

Quantum Physics · Physics 2023-10-16 J. Allam , A. Matzkin

Wigner's friend paradoxes highlight contradictions between measurements made by Friends inside a laboratory and superobservers outside a laboratory, who have access to an entangled state of the measurement apparatus. The contradictions lead…

The extended Wigner's friend problem deals with two Observers each measuring a sealed laboratory in which a friend is making a quantum measurement. We investigate this problem by relying on the basic rules of quantum mechanics as exposed by…

Quantum Physics · Physics 2021-10-19 D. Sokolovski , A. Matzkin

The Wigner's friend experiment is a thought experiment in which a so-called superobserver (Wigner) observes another observer (the friend) who has performed a quantum measurement on a physical system. In this setup Wigner treats the friend,…

Quantum Physics · Physics 2024-09-25 Veronika Baumann , Časlav Brukner

The Wigner's friend type of thought experiments manifest the conceptual challenge on how different observers can have consistent descriptions of a quantum measurement event. In this paper, we analyze the extended version of Wigner's friend…

Quantum Physics · Physics 2019-11-12 Jianhao M. Yang

The Wigner's friend thought experiment was intended to illustrate the difficulty one has in describing an agent as a quantum system when that agent performs a measurement. While it does pose a challenge to the orthodox interpretation of…

Quantum Physics · Physics 2024-09-12 David Schmid , Yìlè Yīng , Matthew Leifer

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 Physics · Physics 2023-05-17 Aníbal Utreras-Alarcón , Eric G. Cavalcanti , Howard M. Wiseman

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…

Quantum Physics · Physics 2023-10-10 Veronika Baumann

The Wigner's Friend (WF) thought experiment concerns quantum measurements by a 'superobserver' of an observer measuring a quantum system. Variations on the setup and its extended versions have seen a resurgence in recent years, in light of…

Quantum Physics · Physics 2025-07-30 Tom Rivlin , Sophie Engineer , Veronika Baumann

The decoherence interpretation of quantum measurements is applied to Wigner's friend experiments. A framework in which all the experimental outcomes arise from unitary evolutions is proposed. Within it, a measurement is not completed until…

Quantum Physics · Physics 2020-03-25 Armando Relaño

Wigner's friend thought experiment is intended to reveal the inherent tension between unitary evolution and measurement collapse. On the basis of Wigner's friend experiment, Brukner derives a no-go theorem for observer-independent facts. We…

Quantum Physics · Physics 2023-06-23 Dong Ding , Can Wang , Ying-Qiu He , Tong Hou , Ting Gao , Feng-Li Yan

"The unambiguous account of proper quantum phenomena must, in principle, include a description of all relevant features of experimental arrangement" (Bohr). The measurement process is composed of pre-measurement (quantum correlation of the…

Quantum Physics · Physics 2021-04-12 Marek Żukowski , Marcin Markiewicz

An experiment by Proietti {\it et al} purporting to instantiate the `Wigner's Friend' thought experiment is discussed. It is pointed out that the stated implications of the experiment regarding the alleged irreconcilability of facts…

Quantum Physics · Physics 2023-03-30 R. E. Kastner

Wigner's Friend scenarios push the boundaries of quantum theory by modeling agents, along with their memories storing measurement outcomes, as physical quantum systems. Extending these ideas beyond quantum theory, we ask: in which physical…

Quantum Physics · Physics 2025-10-08 Nuriya Nurgalieva , V. Vilasini

It is commonly expected that quantum theory is universal, in that it describes the world at all scales. Yet, quantum effects at the macroscopic scale continue to elude our experimental observation. This fact is commonly attributed to…

Wigner's friend experiment and its modern extensions display the ambiguity of the quantum mechanical description regarding the assignment of quantum states. While the friend applies the state-update rule to the system upon observing an…

Quantum Physics · Physics 2025-10-22 Flavio Del Santo , Gonzalo Manzano , Caslav Brukner

The measurement problem is seen as an ambiguity of quantum mechanics, or, beyond that, as a contradiction within the theory: Quantum mechanics offers two conflicting descriptions of the Wigner's-friend experiment. As we argue in this note…

Quantum Physics · Physics 2019-12-09 Arne Hansen , Stefan Wolf

In a joint paper Jeff Bub and Itamar Pitowski argued that the quantum state represents `the credence function of a rational agent [...] who is updating probabilities on the basis of events that occur'. In the famous thought experiment…

Quantum Physics · Physics 2019-02-01 Veronika Baumann , Časlav Brukner

The quantum measurement problem can be regarded as the tension between the two alternative dynamics prescribed by quantum mechanics: the unitary evolution of the wave function and the state-update rule (or "collapse") at the instant a…

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