Protected ground states in short chains of coupled spins in circuit quantum electrodynamics

TL;DR

This paper investigates how non-local interactions in a chain of superconducting qubits can create highly protected ground states, potentially useful for robust quantum information storage and revealing topological edge states.

Contribution

It demonstrates the emergence of a new phase with highly protected ground states due to non-local interactions in a superconducting qubit chain.

Findings

Identification of a phase with protected ground states against local perturbations

Potential observation of topological edge states in small superconducting qubit chains

Analysis of non-local interactions' role in quantum state protection

Abstract

The two degenerate ground states of the anisotropic Heisenberg (XY) spin model of a chain of qubits (pseudo-spins) can encode quantum information, but their degree of protection against local perturbations is known to be only partial. We examine the properties of the system in the presence of non-local spin-spin interactions, possibly emerging from the quantum electrodynamics of the device. We find a phase distinct from the XY phase admitting two ground states which are highly protected against all local field perturbations, persisting across a range of parameters. In the context of the XY chain we discuss how the coupling between two ground states can be used to observe signatures of topological edge states in a small controlled chain of superconducting transmon qubits.