Department of Physics & Centre for Quantum Coherence, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
Sci Rep. 2017 Aug 29;7(1):9756. doi: 10.1038/s41598-017-08183-8.
Berry phases and gauge structures are fundamental quantum phenomena. In linear quantum mechanics the gauge field in parameter space presents monopole singularities where the energy levels become degenerate. In nonlinear quantum mechanics, which is an effective theory of interacting quantum systems, there can be phase transitions and hence critical surfaces in the parameter space. We find that these critical surfaces result in a new type of gauge field singularity, namely, a conic singularity that resembles the big bang of a 2 + 1 dimensional de Sitter universe, with the fundamental frequency of Bogoliubov excitations acting as the cosmic scale, and mode softening at the critical surface, where the fundamental frequency vanishes, causing a causal singularity. Such conic singularity may be observed in various systems such as Bose-Einstein condensates and molecular magnets. This finding offers a new approach to quantum simulation of fundamental physics.
Berry 相位和规范结构是基本的量子现象。在线性量子力学中，参数空间中的规范场呈现出单极奇点，其中能级变得简并。在非线性量子力学中，它是相互作用量子系统的有效理论，在参数空间中可能存在相变，因此存在临界曲面。我们发现这些临界曲面导致了一种新的规范场奇点，即类似于二维加一德西特宇宙大爆炸的圆锥奇点，玻色-爱因斯坦凝聚和分子磁体等各种系统中可能会观测到这种圆锥奇点。这一发现为基本物理的量子模拟提供了一种新方法。
