Updating the constraint on the quantum collapse models via kilogram masses

Abstract

Quantum mechanics, which governs all microscopic phenomena, encounters challenges when applied to macroscopic objects that exhibit classical behavior. To address this micro-macro disparity, collapse models such as the Continuous Spontaneous Localization (CSL) and Diosi-Penrose (DP) models have been proposed. These models phenomenologically modify quantum theory to reconcile its predictions with the observed classical behavior of macroscopic systems. Based on previous works\,([Phys.\,Rev\,D,\,95(8):084054\,(2017)] and [Phys.\,Rev.\,D,\,94:124036,\,(2016)]), an improved bound on the collapse model parameters is given using the updated acceleration noise data released from LISA Pathfinder\,([Phys.\,Rev.\,D, 110(4):042004,\,(2024)]). The CSL collapse rate is bounded to be at most $\lambda_{\rm CSL} \leq 8.3\times 10^{-11}$\,$s^{-1}$ at the mili-Hertz band when $r_{\rm CSL}=10^{-7}\,{\rm m}$, and the DP model's regularization cut-off scale is constraint to be $\sigma_{\rm DP}\sim 285.5$\,fm. Furthermore, we discuss the potential advantages of using deep-underground laboratories to test these quantum collapse models. Our results show the quiet seismic condition of the current deep-underground laboratory has the potential to further constrain the CSL collapse model to $\lambda_{\rm CSL}\leq3\times 10^{-11}\,{\rm s}^{-1}$ when $r_{\rm CSL}=10^{-7}\,{\rm m}$.