# Research lines

The core activity of the group is quantum mechanics, with particular attention to its foundations: the measurement problem, the meaning of the wave function, entaglement and nonlocality, the quantum-to-classical transition, the relation between quantum theory and relativity/gravity. Active collaboations include mathematical, theoretical and experimental physicists. The major research lines are:

## Quantum Foundations: the Measurement Problem

Quantum mechanics is undoubtly a successful theory, nevertheless it still puzzles the scientific community. What does it mean that the (microscopic) world is quantum? Stated more simply: what does it really mean that a particle is quantum? What is the role of the wave function? Is it just a mathematical tool to compute probabilities, or does it have a deeper meaning? Is the collapse of the wave function real? How can one reconcile quantum linearity with the lack of macroscopic superpositions? The group is engaged in developing models of spontaneous wave function collapse, aiming at giving a coherent answer to the above questions. Research is done in collaboration with mathematical and theoretical phyicists - to develop better models - and with experimental physicists - to explore novel tests of collapse models and of quantum theory.

## Decoherence and Open Quantum Systems

The microscopic derivation of effecive equations describing complex systems is one of the most fascinating and challenging problems in mathematical and theoretical physics. The problem is particularly interesting in a quantum context where, together with phenomena like dissipation and the approach to equilibrium, which are present also in classical systems, decoherence shows up. Decoherence (loss of quantum coherence) is produced by the interaction of a system with nearby ones. Quantifying these phenomena in realistc models, and deriving appropriate equations, is part of the research activity of the group.

## Quantum Theory and Gravity

The marriage of relativity and quantum theory as always been problemtic. The reasons are mainly two. On the one side, quantum nonlocality (exemplified by the violation of Bell inequalities) creates a direct conflict with special relativistic requirements. On the other side, the unification of quantum and gravitational phenomena has not yet reached the desired goal. On top of this, one should not forget that existing relativistic quantum field theories are plagued by infinities. Crucial questions are still open: how can our world be nonlocal but at the same time be relativistic? Does gravity really need to be quantized? In recent years, several scientists are proposing ideas which differ from the dominant view. The group is engaged in understanding the source of friction between quantum theory and relativity.

## Collaborations

Active collaborations include:

S. L. Adler, Institute for Advanced Study, Princeton (USA)

D. Dürr, Ludwig-Maximilan University, Munich (Germany)

D.A. Deckert, U.C. Davies (USA)

T. P. Singh, Tata Institute for Fundamental Research, Mumbai (India)

H. Ulbricht, Department of Physics and Astronomy, University of Southampton (UK)

M. Arndt, Physics Faculty, University of Vienna (Austria)

B. C. Hiesmayr, Faculty of Physics, University of Vienna (Austria)

C. Curceanu, LNF-INFN, Frascati (Italy)

M. Paternostro, School of Mathematics and Physics, Queen's University Belfast (UK)