原子腔系统中的量子多体现象研究

在本项目中，我们主要研究了腔量子电动力学结合冷原子体系的多体量子现象。众所周知，在以前的原子腔系统的研究中，原子间的关联效应通常是被忽略的。当我们考虑"热"原子时，原子间的关联通常会被热涨落所破坏，在这种情况下，这个假设是合理的。但是，对于超冷原子，由于热运动被压制，原子间的关联效应就变得显著起来，产生很多新奇的多体量子现象，比如玻色爱因斯坦凝聚，BCS超流性等。另一方面，原子和腔场之间的耦合会形成新的准粒子----"polariton"，并在一定条件下发生凝聚而进入超辐射相。因此，当我们处理腔量子电动力学结合超冷原子时，我们必须同时处理原子间的关联和原子腔之间的耦合。为了这个目的，我们首先求解这个体系的少体问题，为多体问题奠定基础。在此之上，我们主要考虑这个体系的基态问题。由于这个体系的独特性，我们期待能找到一些新奇的量子相。本项研究将加深我们对原子腔体系的理解，为将来的实验提供帮助。

In this program, we study the many body behaviors in Cavity QED with cold atoms. As it well known, quantum correlations between atoms used to be neglected in atom-cavity systems. Such assumption is valid when the atoms are "hot", where the quantum correlations are usually destroyed by the thermal fluctuations. However, for ultracold atoms, thermal fluctuations are generally strongly suppressed and the quantum correlation effects become significant and give rise to many exotic many-body phenomena, such as Bose-Einstein condensation, BCS superfluidity and so on. On the other hand, coupling between cavity field and atom tends to form "polariton", which can condense into a superradiant phase. Then, when we deal with Cavity QED with ultracold atoms, we should treat atomic correlations and atom-cavity coupling on equal footing. For this purpose, we first start from the few-body (like two-body) problem of this system, which is useful for the investigation of many-body problems. Afterwards, we would study ultracold quantum gases interact with a single mode cavity field, mainly focusing on the possible ground states. Beyond the conventional scenarios, we expect some exotic quantum phases could be found in this system. This research can deepen the understanding of atom-cavity systems and may be beneficial for the future experiments.