Quantum spin helices more stable than the ground state: onset of helical protection

TL;DR

This paper demonstrates that quantum spin helices can be more stable than the ground state due to topological protection, with potential applications in quantum information storage and stabilization of helical structures.

Contribution

It introduces a new helical protection mechanism in quantum spin chains, identifying stable spin helices and connecting them to topological sectors, including a newly discovered phantom helix type.

Findings

Spin-current-maximizing helices can exceed ground-state stability.

Helicity (left/right rotation) enhances stability.

Discovery of a new type of phantom helices.

Abstract

Topological magnetic structures are promising candidates for resilient information storage. An elementary example are spin helices in one-dimensional easy-plane quantum magnets. To quantify their stability, we numerically implement the stochastic Schr\"odinger equation and time-dependent perturbation theory for spin chains with fluctuating local magnetic fields. We find two classes of quantum spin helices that can reach and even exceed ground-state stability: Spin-current-maximizing helices and, for fine-tuned boundary conditions, the recently discovered "phantom helices". Beyond that, we show that the helicity itself (left- or right-rotating) is even more stable. We explain these findings by separated helical sectors and connect them to topological sectors in continuous spin systems. The resulting helical protection mechanism is a promising phenomenon towards stabilizing helical quantum structures, e.g., in ultracold atoms and solid state systems. We also identify an - up to our knowledge - previously unknown new type of phantom helices.