Topological and nontopological edge states induced by qubit-assisted coupling potentials

TL;DR

This paper explores how qubit-assisted coupling potentials in a circuit QED lattice modeled after the SSH chain can induce various topological and nontopological edge states, revealing new phase transitions and edge phenomena.

Contribution

It demonstrates the ability to induce and control multiple topological and nontopological edge states via coupling potentials in circuit QED systems, including novel phase transitions.

Findings

Strong coupling potentials induce new topological phases with nontopological edge states.

Multiple phase transitions occur with unbalanced coupling potentials at both ends.

The system exhibits three distinct phases with multiple energy band flips.

Abstract

In the usual Su-Schrieffer-Heeger (SSH) chain, the topology of the energy spectrum is divided into two categories in different parameter regions. Here we study the topological and nontopological edge states induced by qubit-assisted coupling potentials in circuit quantum electrodynamics (QED) lattice system modelled as a SSH chain. We find that, when the coupling potential added on only one end of the system raises to a certain extent, the strong coupling potential will induce a new topologically nontrivial phase accompanied with the appearance of a nontopological edge state in the whole parameter region, and the novel phase transition leads to the inversion of odd-even effect in the system directly. Furthermore, we also study the topological properties as well as phase transitions when two unbalanced coupling potentials are injected into both the ends of the circuit QED lattice system, and find that the system exhibits three distinguishing phases in the process of multiple flips of energy bands. These phases are significantly different from the previous phase induced via unilateral coupling potential, which is reflected by the existence of a pair of nontopological edge states under strong coupling potential regime. Our scheme provides a feasible and visible method to induce a variety of different kinds of topological and nontopological edge states through controlling the qubit-assisted coupling potentials in circuit QED lattice system both in experiment and theory.