While the wave packet of a massive particle grows linearly under free dynamics, it grows exponentially in an inverted harmonic potential, offering a pathway to rapidly increase quantum fluctuations to macroscopic dimensions. In this work, we experimentally demonstrate this principle by expanding the center-of-mass thermal state of a 125nm silica nanoparticle to a position uncertainty of 43.4nm within 260 μs. This expansion, achieved using an inverted dark potential to minimize decoherence from photon recoil, represents a 952-fold increase, reaching a scale comparable to the nanoparticle's physical size. This work represents a key advancement toward preparing macroscopic quantum superpositions at unprecedented mass and length scales.
@article{arxiv.2503.20707,
title = {Accelerated State Expansion of a Nanoparticle in a Dark Inverted Potential},
author = {Gregoire F. M. Tomassi and Daniel Veldhuizen and Bruno Melo and Davide Candoli and Andreu Riera-Campeny and Oriol Romero-Isart and Nadine Meyer and Romain Quidant},
journal= {arXiv preprint arXiv:2503.20707},
year = {2025}
}