Speaker
Andreas Läuchli
Description
The low-energy spectra of many body systems on a torus, of
finite size L, are well understood in magnetically ordered and
gapped topological phases. However, the spectra at quantum
critical points separating such phases are largely unexplored
for 2+1D systems. Using a combination of analytical and
numerical techniques, we show that the low-energy torus
spectrum at criticality provides a universal fingerprint of the
underlying quantum field theory, with the energy levels given
by universal numbers times 1/L. We highlight the implications
of a neighboring topological phase on the spectrum by
studying the Ising* transition, in the example of the toric
code in a longitudinal field, and advocate a phenomenological
picture that provides insight into the operator content of the
critical field theory.