具有变味相互作用的双模玻色子凝聚
Bosons condensed in two modes with flavour-changing interaction
摘要：
考虑了$N$玻色子在味变接触相互作用下的两个正交单粒子模的量子模型。量子基态可以很好地近似为两个准经典态的相干叠加（零温度）或混合（低温）。在平均场描述中，系统通过自发对称性破缺实现这些状态之一。在一定的参数范围内，这两种平均场态都具有有限的角动量，并表现出与量子基态相反的时间反演对称性破缺。在平均场水平和直接对角化的相图进行了探索。利用PenroseOnsager判据分析了零温和有限温下量子基态的性质。三个可能的阶段之一，显示在单粒子水平上的碎裂连同有限对序参量。热和量子涨落的特点是相对于区域的普遍标度行为。非平衡态动力学显示了一个尖锐的过渡之间的自陷和对隧穿制度。讨论了最近实现的一个实验实现，玻色子原子凝聚在二分二维光晶格的第二能带的两个不等价的能量最小值$X_{\pm}$。
英文摘要：
A quantum model is considered for $N$ bosons populating two orthogonal single-particle modes with tunable energy separation in the presence of flavour-changing contact interaction. The quantum ground state is well approximated as a coherent superposition (for zero temperature) or a mixture (at low temperature) of two quasi-classical states. In a mean field description, the systems realizes one of these states via spontaneous symmetry breaking. Both mean field states, in a certain parameter range, possess finite angular momentum and exhibit broken time-reversal symmetry in contrast to the quantum ground state. The phase diagram is explored at the mean-field level and by direct diagonalisation. The nature of the quantum ground state at zero and finite temperature is analyzed by means of the Penrose Onsager criterion. One of three possible phases shows fragmentation on the single-particle level together with a finite pair order parameter. Thermal and quantum fluctuations are characterized with respect to regions of universal scaling behavior. The non-equilibrium dynamics shows a sharp transition between a self-trapping and a pair-tunneling regime. A recently realized experimental implementation is discussed with bosonic atoms condensed in the two inequivalent energy minima $X_{\pm}$ of the second band of a bipartite two-dimensional optical lattice.
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