Improved noninterferometric test of collapse models using ultracold cantilevers

TL;DR

This paper reports on ultracold cantilever experiments that set new upper limits on collapse models, observing nonthermal noise consistent with CSL predictions but ruling out many alternative explanations.

Contribution

It introduces a high-Q, millikelvin cooled cantilever experiment that improves bounds on collapse models by an order of magnitude and investigates unexplained force noise.

Findings

Detected nonthermal force noise compatible with CSL heating

Ruled out several physical mechanisms for the observed noise

Potential to significantly tighten constraints on collapse models

Abstract

Spontaneous collapse models predict that a weak force noise acts on any mechanical system, as a consequence of the collapse of the wave function. Significant upper limits on the collapse rate have been recently inferred from precision mechanical experiments, such as ultracold cantilevers and the space mission LISA Pathfinder. Here, we report new results from an experiment based on a high-Q cantilever cooled to millikelvin temperatures, which is potentially able to improve the current bounds on the continuous spontaneous localization (CSL) model by 1 order of magnitude. High accuracy measurements of the cantilever thermal fluctuations reveal a nonthermal force noise of unknown origin. This excess noise is compatible with the CSL heating predicted by Adler. Several physical mechanisms able to explain the observed noise have been ruled out.ler. Several physical mechanisms able to explain the observed noise have been ruled out.