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arXiv 2007.09842quant-phcond-mat.quant-gas
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慢非绝热量子动力学下的涌现拓扑

Emergent topology under slow non-adiabatic quantum dynamics

Junchen Ye, Fuxiang Li

摘要:

利用非平衡猝灭动力学表征平衡态拓扑量子相,为检测平衡态拓扑不变量提供了一种新的有效方法。然而,大多数以前的研究都集中在理想的突然淬火制度。本文提出了一种通用的非绝热慢猝灭系统哈密顿量的方案,并研究了拓扑相的非绝热动力学表征方案。通过引入一个类似库仑的Landau-Zener问题实现了{ \it slow}猝灭方案,该方案能够统一描述猝灭区(深度非绝热极限)到绝热区的过渡.通过解析地得到非绝热演化后的末态矢量,我们可以计算出时间平均自旋极化率和相应的拓扑自旋织构。我们发现,淬火后的哈密顿量的拓扑不变量的特点是直接的带反转表面上的自旋织构的值。与必须采取额外步骤来计算自旋极化的{ \it梯度}的突然猝灭机制相比,这种非绝热表征提供了检测拓扑不变量的{ \it最小}方案。我们的研究结果不仅适用于库仑猝灭方案下的一维和二维拓扑相,也适用于高维体系或不同猝灭方案。

英文摘要:

Characterization of equilibrium topological quantum phases by non-equilibrium quench dynamics provides a novel and efficient scheme in detecting topological invariants defined in equilibrium. Nevertheless, most of the previous studies have focused on the ideal sudden quench regime. Here we provide a generic non-adiabatic protocol of slowly quenching the system Hamiltonian, and investigate the non-adiabatic dynamical characterization scheme of topological phase. The {\it slow} quench protocol is realized by introducing a Coulomb-like Landau-Zener problem, and it can describe, in a unified way, the crossover from sudden quench regime (deep non-adiabatic limit) to adiabatic regime. By analytically obtaining the final state vector after non-adiabatic evolution, we can calculate the time-averaged spin polarization and the corresponding topological spin texture. We find that the topological invariants of the post-quench Hamiltonian are characterized directly by the values of spin texture on the band inversion surfaces. Compared to the sudden quench regime, where one has to take an additional step to calculate the {\it gradients} of spin polarization, this non-adiabatic characterization provides a {\it minimal} scheme in detecting the topological invariants. Our findings are not restricted to 1D and 2D topological phases under Coulomb-like quench protocol, but are also valid for higher dimensional system or different quench protocol.

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