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arXiv 0901.4778cond-mat.stat-mechcond-mat.quant-gas
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Dicke和Lipkin-Meshkov-Glick模型中的量子相变动力学

Dynamics of quantum phase transitions in Dicke and Lipkin-Meshkov-Glick models

A. P. Itin, P. Törmä

摘要:

我们考虑迪克模型的动力学,有和没有反向旋转条款,在缓慢变化的参数,驱动系统通过量子相变。在Landau-Zener模型的多体推广和通过二阶量子相变(QPT)的动力学通道的背景下,看到没有反旋项和扫频失谐的模型。当参数超过临界值时,绝热性被破坏。应用基于经典绝热不变量的概念和映射到第二Painleve方程(PII)的半经典分析,我们导出了一个公式,它精确地描述了粒子在Hilbert空间中的分布在很宽的参数范围和系统的初始条件。我们发现了粒子分布的显著普适特征,这些特征可以在费什巴赫共振通道实验或腔QED实验中探测到。动态被发现是至关重要的扫描方向上的依赖。最近,在超冷原子气体的腔体实验中实现了具有反转项的模型。它的半经典动力学是由一个具有两个自由度的哈密顿系统描述的。通过QPT对应于通过分叉,并且也可以通过PII(在对快速变量进行平均之后)来描述,从而导致类似的普适分布。在一定条件下,Dicke模型退化为Lipkin-Meshkov-Glick模型.

英文摘要:

We consider dynamics of Dicke models, with and without counterrotating terms, under slow variations of parameters which drive the system through a quantum phase transition. The model without counterrotating terms and sweeped detuning is seen in the contexts of a many-body generalization of the Landau-Zener model and the dynamical passage through a second-order quantum phase transition (QPT). Adiabaticity is destroyed when the parameter crosses a critical value. Applying semiclassical analysis based on concepts of classical adiabatic invariants and mapping to the second Painleve equation (PII), we derive a formula which accurately describes particle distributions in the Hilbert space at wide range of parameters and initial conditions of the system. We find striking universal features in the particle distributions which can be probed in an experiment on Feshbach resonance passage or a cavity QED experiment. The dynamics is found to be crucially dependent on the direction of the sweep. The model with counterrotating terms has been realized recently in an experiment with ultracold atomic gases in a cavity. Its semiclassical dynamics is described by a Hamiltonian system with two degrees of freedom. Passage through a QPT corresponds to passage through a bifurcation, and can also be described by PII (after averaging over fast variables), leading to similar universal distributions. Under certain conditions, the Dicke model is reduced to the Lipkin-Meshkov-Glick model.

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