橡树岭国家实验室在磁性材料中观测到长寿命非平衡量子态：激光驱动下磁振子违反细致平衡，成果发表于《自然-通讯》
美国能源部橡树岭国家实验室与合作者的研究团队在磁性材料中观测到一种长寿命量子态，成果发表于《自然-通讯》。团队用激光脉冲把材料推出正常静息状态，再用中子散射在显微尺度上观察其磁行为。
研究对象是磁振子，一种对材料磁行为至关重要的量子准粒子。实验在能源部科学办公室用户设施散裂中子源上进行，激光驱动与中子散射的组合在非平衡研究中并不常用。
测量结果显示，材料违反了被称作细致平衡的物理规则。在静息系统中，细致平衡以可预测的方式联系着得能量与失能量的过程；在快速激光脉冲下，这一平衡被打破，中子数据只在一侧出现额外信号。
更出乎意料的是，这一非平衡状态没有迅速消失。单侧过剩的磁振子持续存在，团队据此判断这不是短暂的加热效应，而是由周期性激光脉冲维持的长寿命非平衡稳态。
橡树岭国家实验室的 Chengyun Hua 表示，此前从没有人在凝聚态系统中直接探测到细致平衡的违反，理论上说得通，实验上亲眼看到则非常难得。
团队表示，这一观测使该系统成为实时研究其他非平衡量子物理的平台，相关方法也为中子散射在材料被主动驱动时能揭示什么提供了新的基准。
Oak Ridge National Laboratory Team Observes a Long-Lived Nonequilibrium Quantum State in a Magnetic Material: Laser-Driven Magnons Violate Detailed Balance, Published in Nature Communications
Researchers at the Department of Energy Oak Ridge National Laboratory and their collaborators have observed a long-lived quantum state in a magnetic material, in findings published in Nature Communications. The team used rapid laser pulses to drive the material out of its normal resting state and used neutron scattering to study the microscopic details of its magnetic behavior.
The team studied magnons, quantum quasiparticles whose wavelike excitations are critical to magnetic behavior in materials. The neutron measurements were made at the Spallation Neutron Source, a DOE Office of Science user facility, in a combined approach the release described as not typically used for nonequilibrium studies.
The measurements showed that the material violated a physical rule called detailed balance. In a system at rest, detailed balance links energy-gaining and energy-losing events in a predictable way; under the rapid laser pulses, that balance broke, and the neutron data showed extra signals only on one side.
The nonequilibrium state also did not quickly disappear. The lopsided excess magnons persisted, indicating that the team was seeing a long-lived nonequilibrium steady state sustained by periodic laser pulsing rather than a brief heating effect.
Chengyun Hua of Oak Ridge National Laboratory said no one before has directly probed a detailed balance violation in a condensed matter system, and that while it makes theoretical sense, seeing it experimentally was remarkable.
The team said the observation makes the system a strong platform for studying other nonequilibrium quantum physics in real time, and gives scientists a new benchmark for what neutron scattering can reveal when materials are observed while actively driven.
来源： https://phys.org/news/2026-11-laser-driven-magnetic-state-defies.html
发布：GSM·美国（发布链接）
图片来源：Wikipedia/Wikimedia Commons 词条主图：Oak Ridge, Tennessee
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