光晶格中多组分超冷原子气体的量子相变及多体冷却技术的研究

Study of ultracold gases in an optical lattice, a quantum simulator of many-body quantum physics in the field of condensed matter physics, is one of the most active areas in contemporary physics. Particularly, Exploring quantum many-body effects and many-body cooling scheme is an important issue for understanding quantum phenomena, including quantum magnetism and high-Tc superconductivity, and designing macroscopic quantum materials. However, The requirements to observe these novel quantum phenomena in ultracold gases are to achieve extremely low temperature of the order of 100 pK, which is still out of reach experimentally, and new cooling schemes are needed. In this project, we study novel quantum phases and thermodynamical properties of ultracold multi-component bosonic gases in an optical lattice and focus on interaction induced cooling scheme towards novel quantum phases, based on dynamical mean field theory. First, we study bosonic many-body systems loaded into optical lattices, which is well described by Bose-Hubbard model, and obtain zero- and finite-temperature phase diagrams of these systems. Second, we study finite-temperature thermodynamical properties of quantum many-body systems, and focus on changes of critical temperature and entropy of competing phases against interactions. Finally, we investigate the interplay between contact and long-range interactions and their influence on stability and thermodynamical properties of these phases, and describes interaction induced cooling scheme in the adiabatical processes, which are most often used experimentally. We expect our work to provide valuable insight for realizing novel quantum phases in upcoming experiments.

利用光晶格中装载的超冷原子气体模拟凝聚态物理中的微观机理是当前最活跃的前沿课题之一。其中研究量子多体效应对光晶格中强关联系统的影响，探索新的量子多体冷却手段，对量子磁化效应、高温超导理论以及宏观量子材料的设计有很重要的意义。然而理论研究表明光晶格中超冷原子的磁化临界转变温度约100 pK,实验室中需要新的冷却手段才能达到这个临界温度。本项目基于动力学平均场理论，研究强关联效应以及自旋自由度对超冷原子气体性质的影响。具体来讲，基于改进的Hubbard模型利用动力学平均场理论对实验室条件下的超冷原子气体进行数值模拟，获得光晶格中多组分强关联玻色系统的零温和有限温度下的相图；其次，研究量子多体系统的热力学性质，给出相的临界温度以及熵随温度、相互作用的变化；最后，探讨原子之间的接触势以及长程偶极势对整个体系性质的影响，研究相互作用引起的量子多体冷却机制，以便对当前的实验进展进行理论的指导与建议。

利用光晶格中装载的超冷原子气体模拟凝聚态物理中的微观机理是当前最活跃的前沿课题之一。其中,研究量子多体效应对光晶格中强关联系统的影响，对量子磁化效应、高温超导理论以及宏观量子材料的设计有很重要的意义。本项目基于动力学平均场理论，研究强关联效应以及自旋自由度对超冷原子气体性质的影响。首先，基于改进的Hubbard 模型利用动力学平均场理论对实验室条件下的超冷原子气体进行数值模拟，获得光晶格中强关联的旋量玻色系统的零温和有限温度下的相图；其次，研究大自旋体系的基本性质，探讨量子涨落对体系性质的影响；最后，探讨原子之间的接触势以及长程偶极势对整个体系性质的影响，研究相互作用引起的量子多体冷却机制，以便对当前的实验进展进行理论的指导与建议。