半经典磁振子系统中的量子费舍尔信息
Quantum Fisher Information in semiclassical magnon systems
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中文总结 AI 辅助
研究通过简单理论自旋系统阐述凝聚态中QFI的意义，用有限尺寸自旋系统及半经典受挫自旋模型说明其能量化量子纠缠程度与磁振子压缩程度，还展示了相关量子相，表明QFI可作纠缠下限及动量分辨探针，为量子临界现象提供新视角。
中文摘要 AI 辅助
量子费舍尔信息（QFI）是见证固态材料中多体量子纠缠的有力光谱工具，但如何将其与凝聚态系统的其他特性联系起来并不总是显而易见。在本研究中，我们通过研究简单的理论自旋系统来阐述凝聚态中QFI的意义和解释。我们用有限尺寸自旋系统说明QFI量化了波函数内动量相关的量子纠缠程度（即给定波矢处的纠缠深度）。随后用半经典受挫自旋模型表明，在线性自旋波理论（LSWT）背景下，QFI量化了基态中磁振子压缩的动量相关程度。在具有零能量戈德斯通模式的反铁磁体中，LSWT失效，QFI（和纠缠深度）在磁有序波矢处发散。我们还展示了受挫自旋系统中出现的量子相的例子，这些量子相不出现在经典相图中。当接近这些出现的相时，QFI在动量空间的多个波矢处发散。总之，QFI不仅有助于作为纠缠深度的下限，还作为纠缠的动量分辨探针，为量子临界现象提供了新视角。
英文摘要
Quantum Fisher Information (QFI) is a powerful spectroscopic tool to witness many-body quantum entanglement in solid state materials, but it is not always obvious how to relate it to other characteristics of condensed matter systems. In this study we elaborate on the meaning and interpretation of QFI in condensed matter by examining simple theoretical spin systems. We use finite sized spin systems to illustrate that QFI quantifies the momentum- dependent degree of quantum entanglement (that is the entanglement depth at a given wave vector) within a wave function. We subsequently use semiclassical frustrated spin models to show that, in the context of linear spin wave theory (LSWT), QFI quantifies the momentum-dependent degree of magnon squeezing in the ground state. In antiferromagnets with a zero-energy Goldstone mode, LSWT breaks down and QFI (and entanglement depth) diverges at the magnetic ordering wave vector. We also show examples of emergent quantum phases in frustrated spin systems that do not appear in classical phase diagrams. When these emergent phases are approached, QFI diverges across multiple wave vectors in momentum space. Taken together, QFI is not only helpful as a lower bound for entanglement depth, but serves as a momentum-resolved probe of entanglement that offers a novel perspective on quantum critical phenomena.
