Intrinsic mixed-state SPT from modulated symmetries and hierarchical structure of anomaly

TL;DR

This paper introduces a new class of intrinsic symmetry-protected topological phases in open quantum systems with modulated symmetries, highlighting their unique boundary anomalies and non-equilibrium nature.

Contribution

It defines intrinsic mixed-state SPT phases with modulated symmetries, constructed via solvable models, and analyzes their boundary anomalies and detection methods.

Findings

Intrinsic mixed-state SPT phases cannot be realized as ground states of gapped Hamiltonians.

Boundary anomalies in mixed states differ from pure states and can be detected through Renyi-N correlation functions.

Hierarchical structure of boundary anomalies is elucidated using flux insertion and charge pumping arguments.

Abstract

We introduce a class of intrinsic symmetry-protected topological mixed-state(mSPT) in open quantum systems that feature modulated symmetries, such as dipole and subsystem symmetries. Intriguingly, these mSPT phases cannot be realized as the ground states of a gapped Hamiltonian under thermal equilibrium. The microscopic form of the density matrix characterizing these intrinsic mixed-state SPT ensembles is constructed using solvable coupled-wire models that incorporate quenched disorder or quantum channels. A detailed comparison of the hierarchical structure of boundary anomalies in both pure and mixed states is presented, utilizing flux insertion and Laughlin's charge pumping arguments. Finally, we explore the salient features of boundary anomalies in the mixed-state ensemble, which can be detected through the Renyi-N correlation function of charged observables.