Non-equilibrium phase transitions in open quantum systems with several absorbing states

• Applicant: Professor Igor Lesanovsky
• Subject Area: Theoretical Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 435696605

Many-body system are intriguing as they can exhibit collective behaviour that is very challenging to predict even when the interactions between fundamental constituents are precisely known. Direct manifestations of collective effects are phase transitions, for example the conversion of a substance from a liquid to a solid phase at low enough temperature. The latter falls into the class of equilibrium phase transitions. Here the state of the system is determined by so-called detailed balance conditions and typically a temperature can be defined. A lot is known about the general classification of phases and phase transitions in this scenario.Far more interesting are so-called non-equilibrium phase transitions. Here, the concept of a unique temperature is typically not applicable and detailed balance conditions are broken. A paradigmatic set of systems that fall into this class are ones that feature absorbing states. These are configurations that can be accessed by the dynamics, but once they have been reached an escape is no longer possible. An example is given by the population dynamics of bacterial colonies where proliferation and death compete. Once all bacteria are dead, the colony is extinct, and to come back from this absorbing state is no longer possible.In the context of condensed matter and statistical physics absorbing state processes have attracted much attention because they can show new types of collective behaviour. Observed features may fall outside the above-mentioned class of equilibrium processes of which the liquid-solid phase transition is one example. Even more interesting is the situation where the microscopic processes are “quantum” in the sense that non-classical effects such superpositions and entanglement play a part in the dynamics. Such scenario is extremely challenging to study as numerical simulations become extremely demanding due an exponential increase of the required computational resources. Moreover, analytical approaches have not reached a degree of maturity that permits to fully understand and classify emerging phases and phase transitions.This project aims at breaking new ground in our understanding of non-equilibrium quantum many-body physics by conducting a systematic study of systems with two or more absorbing states. This effort will deliver progress in the development of numerical and analytical techniques. Moreover, it aims to uncover dynamical collective phenomena, explore the role of symmetres and to classify non-equilibrium phases and transitions among them. The results are expected to be of relevance for a broad range of scientists working on quantum physics, statistical mechanics and – more broadly – conduct research on systems far from equilibrium.

• DFG Programme: Research Grants