Speaker
Description
The Wigner’s Friend thought experiment, where two observers disagree about experimental outcomes due to different models of measurements, has long been used to frame questions in quantum foundations. It has also recently seen a resurgence as a way to produce novel nonclassical effects such as the Local Friendliness Inequalities (LFIs). But few works have approached these topics using the powerful tools of decoherence theory. Here we study WF scenarios under quantum Darwinism, a framework that describes how environments store information about quantum systems during decoherence. We model the measurement thermodynamically: as a dynamical equilibration process between the system, the friend, and the environment that spreads information between them over time. We then observe how this model affects one’s ability to produce WF-type disagreements and violate LFIs. We find that in our model, the environment produces two novel WF-like effects, including a classical WF analogue. In addition, we numerically observe classicality emerging as the friend and environment grow in size. We also report on ongoing work to understand the relationship between temporal and spatial correlations in WF scenarios, by studying the connections between LFIs and Leggett-Garg inequalities. T. Rivlin, S. Engineer, V. Baumann, arXiv:2507.21221 (2025)