Bethe-Ansatz diagonalization of the steady state of boundary driven integrable spin chains

We find that the density operator of the nonequilibrium steady state (NESS) of XXZ spin chains with strong ‘sink and source’ boundary dissipation, can be described in terms of quasiparticles, with renormalized—dissipatively dressed—dispersion relation. The spectrum of the NESS is then fully accounted for by Bethe ansatz equations for an associated coherent system of these quasiparticles. The dissipative dressing generates an extra singularity in the dispersion relation, which significantly changes the NESS spectrum. In particular, it leads to a dissipation-assisted entropy reduction, due to the suppression in the NESS spectrum of plain wave-type Bethe states in favor of Bethe states localized at the boundaries.