We show that any dynamics collapsing the wave function in space implies diffusion in momentum. This is relevant since it means that, in order to test the validity of thiesse models, and in general of the quantum superposition principle, one can perform experiments, known as “non-interferometric”, which look for this diffusion effect. The main advantage is that these kind of experiments do not require the creation of a large and stable superposition in space, which is typically very hard to do. This approach was successfully employed in the last decade to constrain the parameters of models of spontaneous wave function collapse and it ruled out the simplest version of the Diósi-Penrose model. Until now, one might have argued that the diffusive effects were just a feature of the specific models considered. In this article, we show that this is not the case: ny space-translation covariant dynamics that complies with the no-signaling constraint, if collapsing the wave function in space, must change the average momentum of the system and/or its spread.
S. Donadi, L. Ferialdi and A. Bassi, Collapse Dynamics Are Diffuse, Phys. Rev. Lett. 130, 230202 (2023).
Link to the article: “https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.230202”