On the reality of the quantum state

TL;DR

This paper investigates whether quantum states are real or merely represent information, demonstrating that models treating them as knowledge about underlying physical states conflict with quantum theory.

Contribution

It proves that models where quantum states are purely informational and independent preparations have independent physical states cannot reproduce quantum predictions.

Findings

Models with purely informational quantum states contradict quantum predictions.

Independent preparations must have correlated physical states in such models.

Quantum theory cannot be fully explained by models treating quantum states as mere information.

Abstract

Quantum states are the key mathematical objects in quantum theory. It is therefore surprising that physicists have been unable to agree on what a quantum state truly represents. One possibility is that a pure quantum state corresponds directly to reality. However, there is a long history of suggestions that a quantum state (even a pure state) represents only knowledge or information about some aspect of reality. Here we show that any model in which a quantum state represents mere information about an underlying physical state of the system, and in which systems that are prepared independently have independent physical states, must make predictions which contradict those of quantum theory.