Systems in equilibrium conditions can be effectively investigated by exploiting tools and concepts from thermodynamics. Today, an open challenge is to find equivalently powerful methods to explore many-body systems out of equilibrium.

In our group, we develop and use techniques to investigate the behaviour of these systems: field theories and hydrodynamics to study quench dynamics in closed quantum systems; mean-field approaches and quantum fluctuations to explore critical behaviour and quantum correlations in long-range interacting many-body systems; numerical simulations to describe and classify non-equilibrium phase transitions that occur in the stationary state of open quantum systems; and thermodynamic approaches to analyse phase-transition behaviour that can manifest in quantum trajectories of open quantum systems. 

People: FC, CH, CR, SW

Quantum dynamics is inherently coherent but when quantum systems come in contact with an environment their dynamics becomes decoherent. The environment induces quantum jumps, e.g. photon emission, that can be experimentally observed and the system's state is described by a stochastic mixture of realizations of this process.

In our group is interested in describing the correlations in such open systems and in understanding the effects of environments on quantum systems by engineering system-bath interactions that support emergence of collective properties.

People: FC, CH, SW

Many-particle quantum systems often show low-energy excitations that are qualitatively different from the particles of which they were made.  Sometimes these excitations are also particle-like: a crystal made of fermionic atoms gives rise to quantised bosonic sound waves (phonons); interacting electrons in strong magnetic fields support excitations with fractions of the original electron charge.  Sometimes there are no particles at all at low energies, and the system becomes a sort of 'soup': examples include the Luttinger liquid in d=1 and so-called non-Fermi liquids in d=2 and above.  We try to understand better the known examples of non-trivial strongly correlated behaviour, and to write down and explore new ones.

People: CH, CR, SW

Quantum circuits are many-body models which are discrete in space and time. They provide a versatile platform for exploring quantum phenomena which can incorporate both unitary dynamics and measurements and can be directly implemented in numerous experimental setups. In our group we study the universal properties of these systems including their non-equilibrium phases, entanglement dynamics and the consequences of symmetry.  

People: FC, CH, CR, SW