Pre-entaglement shows that individual quantum systems do not possess states

TL;DR

This paper demonstrates that individual quantum systems do not have definite states prior to measurement, challenging the assumption of preparation independence in quantum theory through an experiment showing pre-entanglement.

Contribution

It provides experimental evidence for pre-entanglement, arguing against the notion that individual quantum systems possess independent states before measurement.

Findings

Pre-entanglement exists at the quantum level.

Individual systems do not possess pre-existing states.

Challenges the assumption of preparation independence.

Abstract

We consider an experiment in which quantum tomography data is collected before and after an entangling measurement performed on two independently prepared, maximally-mixed ensembles. We show that each sub-ensemble that is, as expected, entangled after the measurement is also entangled before it. We call the latter pre-entanglement. If individual systems possessed quantum states, their independent preparations would mean the sub-ensembles were in separable states prior to the entanglement event. The contradiction can be resolved by assigning states only to ensembles and not individual quantum systems. Pre-entanglement found here at the quantum level makes very doubtful the assumption of preparation independence at the ontic level required for a recent theorem.