Скачать или смотреть RCQM/FCMP: Igor A. Zaliznyak: High-temperature quantum coherence in a rare-earth spin chain

Tuesday, Sep./02/2025, 2:00 PM to 3:30 PM (Houston)
Speaker: Igor A. Zaliznyak
Institution: CMPMSD, Brookhaven National Laboratory, Upton

Title: High-temperature quantum coherence in a rare-earth spin chain

Abstract: At high temperatures, quantum effects are generally considered unimportant, giving way to classical behavior. In magnetic systems, when thermal energies exceed the interaction strength between atomic magnetic moments, the spins typically become uncorrelated, resulting in classical paramagnetism. This thermal decoherence of quantum spins 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 [1]. Specific origin of effective quantum spins describing the ground crystal field doublet of Yb J=7/2 spin-orbital multiplet affords an opportunity to study excitations at temperatures much greater than spin interactions. It also provides remarkable sensitivity to specific entangled quantum spin states. We observe a sharply defined spinon continuum, a hallmark of fractionalized excitations in one-dimensional quantum magnets, persisting to temperatures well above the energy scale of Yb-Yb interactions. The observed sharpness of the spinon continuum’s dispersive upper boundary indicates a spinon mean free path exceeding ≈ 35 inter-atomic spacings at temperatures more than an order of magnitude above the interaction energy scale. By Fourier transforming the measured dynamical spin susceptibility we obtain a real space-time linear response function which allows direct measurement of the spinon propagation velocity both at low and high temperature. 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. These results have profound implications for spin systems in quantum information applications operating at finite temperatures and inspire new developments in quantum metrology.

Reference:
[1] L. L. Kish, et al. Nature Communications 16, 6594 (2025);