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arXiv 2008.01085cond-mat.stat-mechcond-mat.quant-gasquant-ph
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破坏Hamilton对称性的观测量的本征态热化及其在相互作用可积系统中的对应

Eigenstate thermalization for observables that break Hamiltonian symmetries and its counterpart in interacting integrable systems

Tyler LeBlond, Marcos Rigol

摘要:

我们研究了非对角矩阵元素的观测值,打破了平移对称的自旋链哈密顿量,并因此连接能量本征态从不同的总准动量部门。我们考虑量子混沌和相互作用的可积点的哈密顿量,并专注于平均能量的中心的频谱。在量子混沌模型中,我们发现存在本征态热化;具体地说,矩阵元素是高斯分布的,方差是$ω=E_α-E_β$的光滑函数({ $E_α$ }是本征能量),尺度为$1/D$($D$是希尔伯特空间维数)。在相互作用的可积模型中,我们发现矩阵元素呈现出一个偏对数正态分布,并有一个方差,这也是一个光滑的函数$ω$的规模为$1/D$。我们详细研究了矩阵元素方差的低频行为,以揭示它表现出扩散或弹道标度的制度。我们表明,在量子混沌模型的方差的行为是定性相似的矩阵元素,连接本征态从相同的准动量部门与不同的。我们还表明,这是不是在相互作用的可积模型的观测值,其conventionally不变的对应不打破可积性,如果作为一个扰动的哈密顿量。

英文摘要:

We study the off-diagonal matrix elements of observables that break the translational symmetry of a spin-chain Hamiltonian, and as such connect energy eigenstates from different total quasimomentum sectors. We consider quantum-chaotic and interacting integrable points of the Hamiltonian, and focus on average energies at the center of the spectrum. In the quantum-chaotic model, we find that there is eigenstate thermalization; specifically, the matrix elements are Gaussian distributed with a variance that is a smooth function of $ω=E_α-E_β$ ({$E_α$} are the eigenenergies) and scales as $1/D$ ($D$ is the Hilbert space dimension). In the interacting integrable model, we find that the matrix elements exhibit a skewed log-normal-like distribution and have a variance that is also a smooth function of $ω$ that scales as $1/D$. We study in detail the low-frequency behavior of the variance of the matrix elements to unveil the regimes in which it exhibits diffusive or ballistic scaling. We show that in the quantum-chaotic model the behavior of the variance is qualitatively similar for matrix elements that connect eigenstates from the same versus different quasimomentum sectors. We also show that this is not the case in the interacting integrable model for observables whose translationally invariant counterpart does not break integrability if added as a perturbation to the Hamiltonian.

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