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arXiv 2409.13623cond-mat.mes-hallcond-mat.quant-gasphysics.opticsquant-ph
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超光谱灵敏度与准长程非厄米趋肤模中的非局域双杂质束缚态

Ultra spectral sensitivity and non-local bi-impurity bound states from quasi-long-range non-hermitian skin modes

Chang Shu, Kai Zhang, Kai Sun

AI总结:

本文证明非厄米系统在热力学极限下能谱对两个相距很远的弱杂质高度敏感,源于非局域双杂质束缚态,并给出解析理论。

摘要:

量子力学的一个基本原理是,量子系统的能谱应保持稳定,不受无穷小且空间局域的微扰影响。在本文中,我们证明这一谱稳定性原理在热力学极限下的非厄米系统中失效。考虑一个无相互作用的非厄米系统 $H_0$,其中包含若干个点状杂质,每个杂质引入一个局域短程势 $V_i$,其中 $i=1, \ldots, n$ 标记杂质。如果杂质势足够弱,引入单个杂质不会改变能谱;即 $H_0$ 与 $H_0 + V_1$ 具有几乎相同的能谱。然而,若引入第二个杂质,即 $H_0 + V_1 + V_2$,我们发现无论这些局域势多么弱,只要它们之间的距离足够大,能谱就可能发生显著改变,这直接违背了传统上对谱稳定性的预期。值得注意的是,这一现象是非局域的,且微扰的影响随两个杂质之间距离的增大而呈指数增长。换言之,尽管哈密顿量完全是局域的,其能谱(对单个无穷小弱杂质的存在视而不见)却能探测到两个相距很远的无穷小弱杂质的存在。利用格林函数技术,我们揭示了这种光谱灵敏度的起源,它源于非局域双杂质束缚态的形成:即波包在两个杂质之间来回传播的非局域稳态。我们提供了一个解析理论来识别和表征这类谱不稳定性,并与数值解完美吻合。

英文摘要:

A fundamental tenet of quantum mechanics is that the energy spectrum of a quantum system shall remain stable against infinitesimally weak and spatially confined perturbations. In this article, we demonstrate that this principle of spectral stability fails in non-Hermitian systems at the thermodynamic limit. Consider, for instance, a non-interacting non-Hermitian system $H_0$ with a couple of point-like impurities, each of which introduces a local short-range potential $V_i$ with $i=1, \ldots, n$ labeling the impurities. If the impurity potentials are sufficiently weak, introducing a single impurity will not alter the spectrum; that is, $H_0$ and $H_0 + V_1$ have nearly identical energy spectra. However, if a second impurity is introduced, $H_0 + V_1 + V_2$, we find that no matter how weak these local potentials are, as long as the distance between them is sufficiently large, significant alterations in the energy spectrum can arise, directly contradicting the traditional expectation of a stable spectrum. Remarkably, this phenomenon is non-local, and the impact of the perturbations increases exponentially with the distance between the two impurities. In other words, although the Hamiltonian is entirely local, its energy spectrum, which is blind to the presence of a single infinitesimally weak impurity, is capable of detecting the presence of two infinitesimally weak impurities separated by a large distance in space. Using Green's function techniques, we uncover the origin of this spectral sensitivity, which arises from the formation of non-local bi-impurity bound states: non-local stationary states with wavepackets propagating back-and-forth between the two impurities. We provide an analytic theory to identify and characterize such spectral instabilities, showing perfect agreement with numerical solutions.

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