Universality in open quantum systems – UNIOPEN

Understanding the dynamics of quantum many-body systems is a central challenge of modern physics. In the past decade, remarkable progress has been made for isolated systems that undergo unitary dynamics. Yet, in reality, quantum systems are always coupled to their environment and the interplay between unitary and non-unitary dynamics should lead to fundamentally new out-of-equilibrium phenomena. This calls for the study of open quantum many-body dynamics, a topic still in its infancy. We propose to thoroughly investigate it through the prism of simple theoretical models of low-dimensional quantum many-body physics, with the goal of grasping their universal aspects.

Our project is centred around three main questions which, in our opinion, lie at the heart of the conundrum of open quantum many-body dynamics :

(1) How do the Lindbladians encoding the dynamics of open quantum systems differ from the Hamiltonians describing the dynamics of their isolated counterparts ? In particular, what critical properties (e.g. diverging correlation lengths) can the stationary states of Lindbladians possess?

(2) How do projective measurements affect the dynamics of quantum many-body systems ? Recently, phase transitions induced by repeated local measurements have been exhibited : how robust are such dynamical phase transitions to changes in the properties of the system ?

(3) What are the physical criteria that discriminate between the descriptions of open quantum systems by Lindbladian evolution and quantum Langevin evolution ? How to quantify the non-Markovian effects ? Can one find effective large-scale descriptions of these dynamics ?

To provide answers to these fundamental questions, the most advanced theoretical and numerical techniques will be exploited. The project will be implemented by our team at the 'Laboratoire de Physique et Chimie Théoriques', which possesses internationally recognised expertise on quantum many-body dynamics and on the theory of critical phenomena.