Probing quantum mechanics using nanoparticle Schr\"odinger cats

TL;DR

This paper demonstrates quantum interference with large sodium nanoparticles, creating macroscopic superposition states that challenge classical intuitions and test macrorealistic modifications of quantum mechanics.

Contribution

It extends matter-wave interference experiments to larger particles, achieving unprecedented macroscopicity and setting new limits on macrorealistic theories.

Findings

Quantum interference observed in sodium nanoparticles with over 7,000 atoms.

Achieved a macroscopicity of μ = 15.5, surpassing previous experiments.

Provided the most stringent exclusion limits for macrorealistic modifications.

Abstract

The quantum superposition principle is a cornerstone of physics and at the heart of many quantum technologies. Yet, it is still often regarded counterintuitive because we do not observe its key features on the macroscopic scales of our daily lives. It is therefore intriguing to ask how quantum properties persist or change as we increase the size and complexity of objects. A paradigmatic test for this question can be realized by matter-wave interferometry, where the motion of individual massive particles becomes delocalized and needs to be described by a wave function that spans regions far larger than the particle itself. Here we present an experimental platform extending matter-wave interference to a qualitatively new class of materials that can vary widely in mass and size. We specifically demonstrate quantum interference of sodium nanoparticles, which can each contain more than 7'000 atoms at masses greater than 170'000 dalton. They propagate in a Schr\"odinger cat state with a macroscopicity of $\mu$ = 15.5, surpassing all previous experiments by an order of magnitude and providing the most stringent exclusion limit for generic macrorealistic modifications of the Schr\"odinger equation to date.