The Quantum Rashomon Effect: A Strengthened Frauchiger-Renner Argument

TL;DR

This paper presents a simplified quantum argument demonstrating that agents' differing perspectives in quantum experiments cannot be unified into a single consistent account, highlighting the limits of information and the Rashomon effect.

Contribution

It introduces a minimal, state-independent setting to demonstrate the Rashomon effect in quantum theory, emphasizing epistemic horizons without relying on entanglement or collapse.

Findings

Agents' predictions contradict observations in simplified quantum scenarios

The Rashomon effect arises from limits on accessible information about systems

A new perspective on quantum inconsistencies based on epistemic horizons

Abstract

The Frauchiger-Renner argument aims to show that `quantum theory cannot consistently describe the use of itself': in many-party settings where agents are themselves subject to quantum experiments, agents may make predictions that contradict observations. Here, we introduce a simplified setting using only three agents, that is independent of the initial quantum state, thus eliminating in particular any need for entanglement, and furthermore does not need to invoke any final measurement and resulting collapse. Nevertheless, the predictions and observations made by the agents cannot be integrated into a single, consistent account. We propose that the existence of this sort of \emph{Rashomon effect}, i.e. the impossibility of uniting different perspectives, is due to failing to account for the limits put on the information available about any given system as encapsulated in the notion of an \emph{epistemic horizon}.