Improved bounds on collapse models from rotational noise of LISA Pathfinder

Spontaneous wavefunction collapse models offer a solution to the quantum measurement problem, by modifying the Schrödinger equation with nonlinear and stochastic terms. The Continuous Spontaneous Localisation (CSL) model is the most studied among these models, with phenomenological parameters that are constrained by experiments. Here, we exploit the recent analysis of LISA Pathfinder’s angular motion data to derive a tighter constraint than previously achieved with translational motion. Moreover, we identify the general conditions for preferring rotational measurement over translational ones for constraining the CSL model.