CMT Seminar - Romain Couvreur (ENS Paris-Saclay) "Entanglement entropy in non-Hermitian critical spin chains"

Entanglement entropy has proven invaluable to our understanding of quantum criticality. It is natural to try to extend the concept to “nonunitary quantum mechanics”, which has seen growing interest from areas as diverse as open quantum systems, noninteracting electronic disordered systems, or nonunitary conformal field theory (CFT). I will discuss such an extension by focusing on the case of one-dimensional quantum group symmetric or supergroup symmetric spin chains. The consideration of left and right eigenstates combined with appropriate definitions of the trace leads to a natural definition of Rényi entropies in a large variety of models. This definition is interpreted geometrically in terms of related loop models and calculate the corresponding scaling in the conformal case. This allows us to distinguish the role of the central charge and effective central charge in rational minimal models of CFT.