Symmetry resolved relative entropies and distances in conformal field theory

We develop a systematic approach to compute the subsystem trace distances and relative entropies for subsystem reduced density matrices associated to excited states in different symmetry sectors of a 1+1 dimensional conformal field theory having an internal U(1) symmetry. We provide analytic expressions for the charged moments corresponding to the resolution of both relative entropies and distances for general integer n. For the relative entropies, these formulas are manageable and the analytic continuation to n = 1 can be worked out in most of the cases. Conversely, for the distances the corresponding charged moments become soon untreatable as n increases. A remarkable result is that relative entropies and distances are the same for all symmetry sectors, i.e. they satisfy entanglement equipartition, like the entropies. Moreover, we exploit the OPE expansion of composite twist fields, to provide very general results when the subsystem is a single interval much smaller than the total system. We focus on the massless compact boson and our results are tested against exact numerical calculations in the XX spin chain.

Automated summary

A systematic approach is developed to compute subsystem trace distances and relative entropies for excited states in a 1+1 dimensional conformal field theory with an internal U(1) symmetry. Analytic expressions for charged moments corresponding to both relative entropies and distances are provided for general integer n. It is found that relative entropies and distances are the same for all symmetry sectors, exhibiting entanglement equipartition, similar to entropies. OPE expansion of composite twist fields is exploited to provide general results for small subsystems compared to the total system.