Study of quasi-conserved quantities in atomic BEC and dilute quantum gases

我们在操纵和控制由原子气体组成的玻色-爱因斯坦凝聚体(BEC)的背景下研究了绝热性和非线性动力学。在一项关于在BEC干涉仪中构建分束器的实验中，我们对意外产生量子涡旋的机制进行了初步研究。由于分析BEC所需的数值技术和计算机程序与超短激光脉冲的数值技术和计算机程序有许多相似之处，并将其应用于超强激光中原子的电离和高次谐波的产生，我们观察到了这一新的发展。考虑到两体相互作用的表示，我们采用了基于理论化学的计算方案，并评估了离子在低温氦气体中的迁移率，从而对迁移率进行了动力学分析，并与实验结果进行了比较。出乎意料的是，我们找到了迄今尚未解决的偏振极限问题的原因。除了这些发现，还出现了新的挑战。例如，原子对在超低温下转变为分子构成了一个非线性STIRAP问题，这是本主题下的一个重要问题，由于非线性STIRAP问题的普遍数学性质，因此更适用于相关问题。我们预计，在低温下多体物理的绝热性和非线性动力学方面将出现更多的挑战。在超短激光脉冲及其与原子的相互作用领域，同样有可能出现一项新的实验发展。我们期待着为取得进一步进展作出贡献。

We studied adiabaticity and nonlinear dynamics in the context of the manipulation and control of the Bose-Einstein condensate (BEC) made of an atomic gas. We conducted a pilot study of the mechanism for the unanticipated creation of quantum vorticies in an experiment pertaining to the construction of a beam-splitter in a BEC-interferometer. Since the numerical techniques and the computer codes required for the analysis of BEC have much in common with those for the ultra-short laser pulses and their application to atomic physics, we observed a new development by applying the techniques to the ionization of atoms in ultra-intense laser fields and to the high-harmonics generation.With a view to the representation of two-body interactions, we employed a computation scheme based on theoretical chemistry, and evaluated the mobility of an ion in a low-temperature gas of helium, thereby carrying out a dynamical analysis of the mobility and comparing it with experimental results. Quite unexpectedly, we pinned down the cause of the hitherto unsolved polarization-limit problem.In addition to such discoveries, there emerged new challenges. For instance, the transformation of an atomic pair into a molecule at ultra-low temperatures constitutes a nonlinear STIRAP problem, which is an important issue under the present theme and is all the more applicable to related problems because of the universal mathematical nature of the nonlinear STIRAP problem. We expect more challenges will appear in relation to the adiabaticity and nonlinear dynamics in many-body physics at low temperatures. A new experimental development is equally likely in the field of ultra-short laser pulses and their interactions with atoms. We look forward to contributing to further progress.