## Foundations of Quantum Mechanics

Quantum mechanics is undoubtedly a successful theory. However, it poses unresolved problems: where is the boundary between the quantum (microscopic) and classical (macroscopic) worlds? How to reconcile quantum linearity with the absence of macroscopic superpositions? What is the role of the wave function? How does it collapse? These are just some of the open problems in the foundations of quantum mechanics. The group is involved in the development and experimentation of models of spontaneous collapse of the wave function, aiming to provide a coherent answer to the above questions. Starting from the fundamental model of Ghirardi, Rimini, and Weber, several models describing the collapse of the wave function have been developed. The group focuses on two main research directions: testing current collapse models, working closely with experimental physicists, and developing their extensions to dissipative and non-Markovian dynamics, as well as the relativistic field.

## Decoherence and Open Quantum Systems

Even in the most sophisticated experimental laboratories, quantum systems are inevitably influenced by the surrounding environment. This action can overshadow the effects one wishes to observe. In addition to phenomena such as dissipation and approaching thermal equilibrium, which are also present in classical systems, in the context of open quantum systems, environmental decoherence plays the most significant role. It is responsible for the loss of quantum coherence and thus the quantum characteristics of the system's dynamics. To reduce environmental action on the system, an accurate derivation and characterization of effective motion equations incorporating these effects are essential. The group works on the modeling and quantification of these phenomena and, in collaboration with experimental partners, aims to test them. A recently developed model concerns gravitational decoherence, where gravity acts as the environment causing the loss of quantum coherence.

## Interplay between Quantum Mechanics and Gravity

The unification of relativity and quantum mechanics has always been problematic. The reasons are mainly two: on the one hand, quantum nonlocality (exemplified by the violation of Bell inequalities) creates a direct conflict with special relativistic requirements; on the other hand, the unification of quantum and gravitational phenomena has not yet achieved the desired goal. In addition, one should not forget that existing relativistic quantum field theories are plagued by divergences. Crucial questions are still open: how can our world be non-local but at the same time relativistic? Does gravity really need to be quantized? How is the gravitational field generated by a quantum superposition modeled? In recent years, several scientists have proposed ideas that differ from the dominant view. The group is committed to understanding the source of friction between quantum theory and relativity/gravity.