Consistency in the description of quantum measurement: Quantum theory can consistently describe the use of itself

TL;DR

This paper proposes minimal modifications to quantum mechanics with additional rules to resolve the Frauchiger-Renner paradox, ensuring consistent descriptions of measurement without contradiction.

Contribution

It introduces two simple rules that extend standard quantum mechanics to consistently interpret measurement processes and avoid paradoxes.

Findings

The rules prevent the paradox by clarifying measurement interpretation.

Different participants may have different measurement perspectives.

The approach maintains consistency within quantum theory.

Abstract

Recent extended formulations of the Wigner's friend thought experiment throw the measurement problem of quantum mechanics into sharper relief. Here I respond to an invitation by Renner to provide a consistent and concrete set of rules for quantum mechanics which can avoid the apparent paradox formulated by Frauchiger and Renner [Nat. Comm. 9, 3711 (2018)]. I propose a slight addition to standard textbook quantum mechanics, in the form of two rules, which avoids the paradox. The first specifies when a given quantum dynamics can be interpreted as a measurement. Potentially any dynamics can, but doing so depends on the context of other performed operations. The second requires that a joint context be used to determine whether several different dynamical evolutions can all be interpreted as measurement. The paradox is then avoided because not every participant in the Frauchiger-Renner thought experiment regards the stated dynamical descriptions of the experiment as measurements.