Collapse models: a challenge to the universality of quantum mechanics
Quantum mechanics revolutionized our understanding of Nature. Its superposition principle describes the possibility of a system being prepared in two distinguishable physical configurations, for example, two distinct positions, and its application has already led to the development of several quantum technologies. Although countless experiments have verified the validity of the quantum theory at the level of single atoms and molecules, its universality up to the macroscopic scale is challenged on the daily basis. At the human scale, we do not perceive quantum superposition, meaning that -- somewhere between the microscopic scale of single atoms and ours – the quantum superposition progressively breaks down. Collapse models describe precisely such an effect, and their testing is pivotal in understanding the limits of the quantum theory.
The last 20 years have seen a growing interest in applications of quantum theory to different physical systems, ranging from cold atoms to mesoscopic mirrors, from phonon dynamics in crystals to macroscopic resonators. Together with the development of the finest preparation and detection techniques, a plethora of different experimental tests of the validity of quantum mechanics -- and that of collapse models – has emerged. In the review article "Present status and future challenges of non-interferometric tests of collapse models" published on 17th February 2021 in Nature Physics, TEQ partners from Queen’s University Belfast, University of Southampton and University of Trieste, describe the present status of the experimental bounds on collapse models, which range from single atoms up to cosmology. They discuss the technical challenges of state-of-art testing and draw the path for future avenues of dedicated experiments.