Verifying quantum superpositions at metre scales

TL;DR

This paper critically examines recent experiments claiming to demonstrate quantum superpositions at metre scales, arguing that observed interference does not definitively prove the existence of such superpositions in massive particles.

Contribution

It challenges prior claims by analyzing the interpretation of interference results, emphasizing that superposition at macroscopic scales remains unconfirmed.

Findings

Interference observed does not conclusively prove superposition.

The experiment's results are consistent with classical explanations.

Persistence of superpositions at metre scales remains unverified.

Abstract

While the existence of quantum superpositions of massive particles over microscopic separations has been established since the birth of quantum mechanics, the maintenance of superposition states over macroscopic separations is a subject of modern experimental tests. In Ref. [1], T. Kovachy et al. report on applying optical pulses to place a freely falling Bose-Einstein condensate into a superposition of two trajectories that separate by an impressive distance of 54 cm before being redirected toward one another. When the trajectories overlap, a final optical pulse produces interference with high contrast, but with random phase, between the two wave packets. Contrary to claims made in Ref. [1], we argue that the observed interference is consistent with, but does not prove, that the spatially separated atomic ensembles were in a quantum superposition state. Therefore, the persistence of such superposition states remains experimentally unestablished.