Wigner's friend and the quasi-ideal clock

TL;DR

This paper explores how quantum clocks, specifically the quasi-ideal clock, affect the Wigner's Friend thought experiment, revealing persistent disagreements and potential paradoxes even with imprecise timing mechanisms.

Contribution

It introduces a quantum clock model into the Wigner's Friend scenario, analyzing its impact on the paradox and the role of timing in quantum measurements.

Findings

No decoherent behavior from the quantum clock approach

Disagreement persists between superobserver and friend despite clock imprecision

Gaussian spread of the clock can influence observable paradoxes

Abstract

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 often called Wigner's Friend Scenarios, which have been providing insights over many frameworks and interpretations of quantum theory. Recently, a no-go theorem obtained by Daniela Frauchiger and Renato Renner brought attention back to the Wigner's Friend and its potential of putting theories to test. Many answers to this result pointed out how timing in the thought experiment could be yielding a paradox. In this work, we ask what would happen if the isolated friend in a Wigner's Friend Scenario did not share a time reference frame with the outer observer, and time should be tracked by a quantum clock. For this purpose, we recollect concepts provided by the theory of quantum reference frames and the quantum resource theory of asymmetry, to learn how to internalize time in this scenario, and introduce a model for a feasible quantum clock proposed by Mischa P. Woods, Ralph Silva and Jonathan Oppenheim, called the quasi-ideal clock. Our results have shown that no decoherent behavior comes from this approach, and the disagreement between the superobserver and its friend persists even for an imprecise clock on Wigner's side. However, the gaussian spread of this clock model can control what observables do not raise a paradox, indicating the relevance of deepening this analysis.