Keywords: quantum many-body systems; broken ergodicity; many-body localisation.
Ergodic systems lie at the heart of condensed matter and statistical physics, since they reach thermal equilibrium and lose memory of their initial conditions, thereby allowing for coarse-grained classical descriptions. Recently, non-ergodic quantum many-body systems, which fail to thermalise and decohere completely, have generated intense research activity. This mini-colloquium will address their fundamental theoretical challenges, including many-body localisation and other forms of novel, non-classical long-time behaviour.
The meeting will bring together established leaders and rising young scholars in this emerging interdisciplinary field, which spans condensed matter, atomic/molecular physics, and quantum information science. The nature of the questions raised are of central importance to all communities dealing with quantum many-particle systems.
The mini-colloquium will include a focus on the following recent developments and associated challenges in the field:
(1) Progress in understanding the stability of a many-body localised phase in disordered low-dimensional systems, in particular the eigenstate phase transition where localisation breaks down and ergodicity is restored.
(2) Many-body localisation (MBL) in non-disordered systems, including fermions in an external field (Stark MBL) and quasiperiodic systems.
(3) Progress in quantum information and related techniques, such as tensor networks, in enabling computational study of large many-body systems.
(4) Kinetically constrained quantum systems, as realised in Rydberg atom quantum simulators, and resultant dynamical phenomena including quantum many-body scars.
(5) Weak ergodicity breaking in clean systems with certain symmetries, and dynamical fracturing of the Hilbert space; as arises in a large class of so-called fracton topological phases.
(6) Many-body localisation as a mechanism for engineering novel out-of-equilibrium quantum phases of matter, such as time crystals.