High-temperature quantum coherence of spinons in a rare-earth spin chain

TL;DR

This study demonstrates that quantum spinons in a Yb spin chain maintain coherence at temperatures much higher than their interaction energy scale, challenging traditional views on thermal decoherence in quantum systems.

Contribution

It reveals high-temperature quantum coherence of spinons in a rare-earth spin chain, expanding understanding of quantum effects at elevated temperatures.

Findings

Spinons persist with sharp spectra at high temperatures.

Spinon mean free path exceeds 35 inter-atomic spacings.

Quantum behavior extends well beyond expected thermal limits.

Abstract

Conventional wisdom dictates that quantum effects become unimportant at high temperatures. In magnets, when the thermal energy exceeds interactions between atomic magnetic moments, the moments are usually uncorrelated, and classical paramagnetic behavior is observed. This thermal decoherence of quantum spin behaviors is a major hindrance to quantum information applications of spin systems. Remarkably, our neutron scattering experiments on Yb chains in an insulating perovskite crystal defy these conventional expectations. We find a sharply defined spectrum of spinons, fractional quantum excitations of spin-1/2 chains, to persist to temperatures much higher than the scale of the interactions between Yb magnetic moments. The observed sharpness of the spinon continuum's dispersive upper boundary indicates a spinon mean free path exceeding $\approx 35$ inter-atomic spacings at temperatures more than an order of magnitude above the interaction energy scale. We thus discover an important and highly unique quantum behavior, which expands the realm of quantumness to high temperatures where entropy-governed classical behaviors were previously believed to dominate. Our results have profound implications for spin systems in quantum information applications operating at finite temperatures and motivate new developments in quantum metrology.