Defect Holonomy Near Rank-Deficient Mixed States
秩亏混合态附近的缺陷和乐
Yu-Huan Huang, Xu-Yang Hou, Hao Guo
AI总结 研究混合量子态在秩变化点附近的几何结构,通过Uhlmann和乐作为渐近不变量来刻画秩亏缺陷的拓扑性质。
Comments 10 pages, 3 figures
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我们研究了秩变化点附近混合量子态的几何结构,表明这些奇点作为有效的几何缺陷。Uhlmann联络仅在密度矩阵流形的满秩部分有良好定义,而秩亏态形成奇异边界层,其中丛结构退化。通过限制在排除奇异集的穿孔态流形上,我们获得了良好定义的规范结构,并识别出一个渐近鲁棒不变量:围绕缺陷的非可缩环的Uhlmann和乐。在一个精确可解的qutrit模型中,出现了一个受限子流形,其上联络局部平坦但具有非平凡单值,类似于具有Aharonov-Bohm型输运的平坦联络。和乐仅依赖于在冻结本征基几何的径向依赖和固定角环下消失本征值的比率。相反,当本征值以不同幂次收缩时,Uhlmann曲率可能路径依赖地发散,具有主导谱前因子标度律,从而确立了和乐作为通用渐近不变量而曲率非通用。在有效SU(2)缺陷扇区内,和乐的共轭类(等价于Wilson环变量)提供了围绕秩亏缺陷的渐近单值的连续非量子化分类。这种非量子化并不意味着缺乏鲁棒性:渐近和乐受穿孔流形拓扑保护,对环或径向轮廓的光滑形变不敏感。
We investigate the geometry of mixed quantum states near rank-changing points, showing that these singularities function as effective geometric defects. The Uhlmann connection is well-defined on the full-rank sector of the density-matrix manifold, while rank-deficient states form singular boundary strata where the bundle structure degenerates. By restricting to a punctured state manifold that excludes the singular set, we obtain a well-defined gauge structure and identify an asymptotically robust invariant: the Uhlmann holonomy around noncontractible loops encircling the defect on a restricted two-dimensional punctured submanifold. In an exactly solvable qutrit model, a restricted submanifold emerges on which the connection is locally flat yet carries nontrivial monodromy, analogous to flat connections with Aharonov--Bohm-type transport. The holonomy depends only on the ratios of the vanishing eigenvalues under frozen radial dependence of the eigenbasis geometry and a fixed angular loop. In contrast, the Uhlmann curvature may diverge path-dependently when eigenvalues shrink with distinct powers, with a leading spectral-prefactor scaling law, establishing that the holonomy survives as a universal asymptotic invariant while the curvature remains non-universal. Within the effective SU(2) defect sector, the conjugacy class of the holonomy, equivalently the Wilson loop variable, provides a continuous, non-quantized classification of the asymptotic monodromy surrounding the rank-deficient defect. This non-quantization does not imply a lack of robustness: the asymptotic holonomy is an invariant of the restricted punctured submanifold and is insensitive to smooth deformations of the loop or the radial profile within the fixed spectral-ratio sector.