Occupation of topological Floquet bands in open systems

TL;DR

This paper investigates how open Floquet topological insulators reach steady states with finite excitations due to dissipation, and explores reservoir engineering to improve band population control.

Contribution

It demonstrates that dissipation leads to persistent excitations in Floquet topological systems and discusses strategies for reservoir engineering to enhance band selectivity.

Findings

Steady states have finite excitations above the effective ground state.

Dissipation prevents perfect population of topological bands.

Reservoir engineering can mitigate excitation issues.

Abstract

Floquet topological insulators are noninteracting quantum systems that, when driven by a time-periodic field, are described by effective Hamiltonians whose bands carry nontrivial topological invariants. A longstanding question concerns the possibility of selectively populating one of these effective bands, thereby maximizing the system's resemblance to a static topological insulator. We study such Floquet systems coupled to a zero-temperature thermal reservoir that provides dissipation. We find that the resulting electronic steady states are generically characterized by a finite density of excitations above the effective ground state, even when the driving has a small amplitude and/or large frequency. We discuss the role of reservoir engineering in mitigating this problem.