We prove a theorem that shows the degeneracy of many-body states depends on total particle number and flux filling ratio, for particles in a periodic lattice and under a uniform magnetic field. Non-interacting fermions and weakly interacting bosons are given as two examples. For the later case, this phenomena can also be understood in terms of destructive quantum interferences of multiple symmetry related tunneling paths between classical energy minima, which is reminiscent of the spin-parity effect discovered in magnetic molecular cluster. We also show that the quantum ground state of a mesoscopic number of bosons in this system is not a simple mean-field state but a fragmented state even for very weak interactions.
Quartic level repulsion in a quantum chaotic three-body system without symplectic symmetry
Te Whai Ao Dodd-Walls Centre for Photonic and Quantum Technologies（光子与量子技术多惠亚奥中心）；Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Studies, Massey University（梅西大学新西兰高级研究院理论与化学物理中心）；Center for Theoretical Physics of Complex Systems, Institute for Basic Science (IBS)（基础科学研究院复杂系统理论物理中心）
Many-body-localization induced protection of symmetry-protected topological order in a XXZ spin model
Huse { \it et al} [Phys. Rev. B { \bf 88}，014206（2013）]和Elisran { \it et al} [Phys. Rev. B 89，144201（2014）]提出了一种反直觉的预期：即使在高激发本征态中，局域化也保护基态的量子顺序。在这项工作中，我们数值研究的本地化保护的拓扑（SPT）秩序考虑修改后的XXZ自旋模型，相关的相互作用的Su-Schrieffer-Heeger（SSH）模型。我们系统地研究了多体局域化（MBL）如何保护SPT对不同类型的疾病和不同形式的相互作用。一定的无序度导致各激发多体本征态的低纠缠谱明显简并。这一事实表明，存在的边缘模式，这是一个标志的SPT秩序，是由MBL在激发多体本征态的保护。此外，我们还报告了如何MBL保护边缘模式在激发多体本征态消失的对角型无序。
