Excited state Rényi entropy and subsystem distance in two-dimensional non-compact bosonic theory. Part II. Multi-particle states

Abstract: We study the excited state R\'enyi entropy and subsystem Schatten distance in the two-dimensional free massless non-compact bosonic field theory, which is a conformal field theory. The discretization of the free non-compact bosonic theory gives the harmonic chain with local couplings. We consider the field theory excited states that correspond to the harmonic chain states with excitations of more than one quasiparticle, which we call multi-particle states. This extends the previous work by the same authors to more general excited states. In the field theory we obtain the exact R\'enyi entropy and subsystem Schatten distance for several low-lying states. We also obtain the short interval expansion of the R\'enyi entropy and subsystem Schatten distance for general excited states. In the locally coupled harmonic chain we calculate numerically the excited state R\'enyi entropy and subsystem Schatten distance using the wave function method. We find excellent matches of the analytical results in the field theory and numerical results in the gapless limit of the harmonic chain. We also make some preliminary investigations of the R\'enyi entropy and the subsystem Schatten distance in the extremely gapped limit of the harmonic chain.