We consider coherent dynamics of cold atoms in a square optical lattice without interference between counter-propagating laser beams. The dynamics is treated within the framework of semi-classical approximation, taking into account a coupling between the atom internal and external degrees of freedom. The corresponding set of equations of motion has been found before to be regular or chaotic in dependence on the values of the control parameters, the detuning between the atomic transition and laser frequencies, and the atom recoil frequency. In this paper, we carry out numerical experiments on spreading of cold atomic clouds in the lattice under different values of the detuning, keeping the recoil frequency to be fixed. The distributions of atoms differ strongly providing a way to control atomic transport by tuning just a single control parameter called the detuning. It is possible to drive cold atoms through different regimes of translational motion, from regular ballistic flights to chaotic walking. A possibility to observe the effect of chaotic walking in real experiments is discussed.

中文翻译：

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方形光学晶格中具有冷原子的图形

我们考虑了方形原子晶格中冷原子的相干动力学，而没有反向传播的激光束之间的干扰。考虑到原子内部和外部自由度之间的耦合，在半经典近似框架内处理动力学。根据控制参数的值，原子跃迁和激光频率之间的失谐以及原子反冲频率，之前已经发现相应的运动方程组是规则的或混沌的。在本文中，我们在不同的失谐值下对冷原子云在晶格中的扩散进行了数值实验，同时保持了后坐频率固定。原子的分布差异很大，仅通过调整称为失谐的单个控制参数即可提供一种控制原子传输的方法。从常规的弹道飞行到混乱的行走，可以通过不同的平移运动来驱动冷原子。讨论了在实际实验中观察混沌行走效果的可能性。