LISA pathfinder appreciably constrains collapse models

TL;DR

LISA Pathfinder's precise acceleration noise measurements place strong constraints on collapse models like CSL and Diosi-Penrose, limiting their parameters and challenging their viability in explaining quantum measurement phenomena.

Contribution

This work provides the first experimental bounds on collapse model parameters using LISA Pathfinder data, significantly constraining their theoretical parameter space.

Findings

Bound the CSL localization rate parameter to at most 2.96×10^{-8} s^{-1}

Set the Diosi-Penrose regularization scale to at least 40.1 fm

Constraints challenge the plausibility of collapse models in quantum mechanics

Abstract

LISA Pathfinder's measurement of a relative acceleration noise between two free-falling test masses with a square root of the power spectral density of $5.2 \pm 0.1 \mbox{ fm s}^{-2}/\sqrt{\rm{Hz}}$ appreciably constrains collapse models. In particular, we bound the localization rate parameter, $\lambda_{\rm CSL}$, in the continuous spontaneous localization model (CSL) to be at most $\left( 2.96 \pm 0.12 \right) \times 10^{-8} \mbox{ s}^{-1}$. Moreover, we bound the regularization scale, $\sigma_{\rm DP}$, used in the Diosi-Penrose (DP) model to be at least $40.1 \pm 0.5 \mbox{ fm}$. These bounds significantly constrain the validity of these models. In particular: (i) a lower bound of $2.2 \times 10^{-8\pm2} \mbox{s}^{-1}$ for $\lambda_{\rm CSL}$ has been proposed in (although a lower bound of about $10^{-17} \mbox{s}^{-1}$ is sometimes used), in order for the collapse noise to be substantial enough to explain the phenomenology of quantum measurement, and (ii) 40 fm is larger than the size of any nucleus, while the regularization scale has been proposed to be the size of the nucleus.