# A generalized perspective on non-perturbative linked cluster expansions

Kai Schmidt, TU Dortmund

14.11.2014 at 09:00

Linked cluster expansions (LCEs) became a standard tool over the last decades to study quantum many-body systems directly in the thermodynamic limit. Recently, many exciting developments have been achieved with nonperturbative LCEs, ranging from the calculation of entanglement entropies to non-equilibrium physics.

Here we identify a fundamental challenge for non-perturbative LCEs resulting from the reduced symmetry on graphs, most importantly the breaking of translational symmetry, when targeting the properties of excited states. A generalized notion of cluster additivity is introduced, which is used to formulate an optimized scheme of graph-based continuous unitary transformations (gCUTs) allowing to solve and to physically understand this fundamental challenge. Most importantly, it demands to go beyond the paradigm of using the exact eigen vectors on graphs.

A 450 - Theresienstr. 37