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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

Considering a complicated extension of a Wigner's friend scenario, Frauchiger and Renner (FR) allegedly showed that "quantum theory cannot consistently describe the use of itself". However, such a result has been under severe criticism, as…

Quantum Physics · Physics 2020-06-30 R. Muciño , E. Okon

The notorious Wigner's friend thought experiment (and modifications thereof) has in recent years received renewed interest especially due to new arguments that force us to question some of the fundamental assumptions of quantum theory. In…

Quantum Physics · Physics 2021-05-18 Philippe Allard Guérin , Veronika Baumann , Flavio Del Santo , Časlav Brukner

The article explores challenges presented by revelations in physics and the questions they provoke concerning reality. It sheds light on the disparity between the indefinite nature of quantum reality and our perception of classical reality.…

General Physics · Physics 2024-05-14 Jahan N. Schad

We show that the quantum description of measurement based on decoherence fixes the bug in quantum theory discussed in [D. Frauchiger and R. Renner, {\em Quantum theory cannot consistently describe the use of itself}, Nat. Comm. {\bf 9},…

Quantum Physics · Physics 2018-10-17 Armando Relaño

It is generally agreed that decoherence theory is, if not a complete answer, at least a great step forward towards a solution of the quantum measurement problem. It is shown here however that in the cases in which a sentient being is…

Quantum Physics · Physics 2009-11-10 Bernard d'Espagnat

The place and role of an Observer in quantum mechanics has been a subject of an ongoing debate since the theory's inception. Wigner brought this question to the fore in a celebrated scenario in which a super-Observer observes a Friend…

Quantum Physics · Physics 2020-09-14 A. Matzkin , D. Sokolovski

Quantum decoherence plays a pivotal role in the dynamical description of the quantum-to-classical transition and is the main impediment to the realization of devices for quantum information processing. This paper gives an overview of the…

Quantum Physics · Physics 2019-11-15 Maximilian Schlosshauer

A theory of everything should not only tell us the laws for matter, gravity, and possibly boundary condition for the universe. In addition, it should specify the relation between theory and experience. Here I argue for a minimal…

Quantum Physics · Physics 2023-06-21 Ding Jia

Decoherence phenomena are pervasive in the arena of nanostructures but perhaps even more so in the study of the fundamentals of quantum mechanics and quantum computation. Since there has been little overlap between the studies in both…

Condensed Matter · Physics 2009-11-10 R. F. O'Connell

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

Quantum theory provides an extremely accurate description of fundamental processes in physics. It thus seems likely that the theory is applicable beyond the, mostly microscopic, domain in which it has been tested experimentally. Here we…

Quantum Physics · Physics 2018-10-08 Daniela Frauchiger , Renato Renner

We briefly review a number of major features of the approach to quantum measurement theory based on environment-induced decoherence of the measuring apparatus, and summarize our observations in the form of a couple of general principles…

Quantum Physics · Physics 2023-06-30 Avijit Lahiri

In 1962, Eugene P. Wigner introduced a thought experiment that highlighted the incompatibility in quantum theory between unitary evolution and wave function reduction in a measurement. This work resulted in a class of thought experiments…

Quantum Physics · Physics 2021-05-19 Vinicius P. Rossi , Diogo O. Soares-Pinto

Decoherence is the main process behind the quantum to classical transition. It is a purely quantum mechanical effect by which the system looses its ability to exhibit coherent behavior. The recent experimental observation of diffraction and…

Quantum Physics · Physics 2008-11-26 Paula I. Villar , Fernando C. Lombardo

Quantum states are described by wave functions whose phases cannot be directly measured, but which play a vital role in quantum effects such as interference and entanglement. The loss of the relative phase information, termed decoherence,…

Chemical Physics · Physics 2019-12-20 Jia Chen , Cong Hu , John F. Stanton , Stephen Hill , Hai-Ping Cheng , Xiao-Guang Zhang

The notorious quantum measurement problem brings out the difficulty to reconcile two quantum postulates: the unitary evolution of closed quantum systems and the wave-function collapse after a measurement. This problematics is particularly…

Quantum Physics · Physics 2022-08-24 George Moreno , Ranieri Nery , Cristhiano Duarte , Rafael Chaves

In this study, we present a modified quantum theory, denoted as $QT^\ast$, which introduces mass-dependent decoherence effects. These effects are derived by averaging the influence of a proposed global quantum fluctuation in position and…

Quantum Physics · Physics 2024-12-18 Heinz-Jürgen Schmidt

The concept of an isolated system, and Frauchiger and Renner's extended `Wigner's friend' scenario are discussed. It is argued that: (i) it is questionable whether the approximation of the isolated system is valid when measurement-like…

Quantum Physics · Physics 2026-05-12 Andrew Steane