Liu Gangqiang, Snoke David W, Daley Andrew, Pfeiffer Loren N, West Ken
Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260;
Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260; Department of Physics and Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG, United Kingdom; and.
Proc Natl Acad Sci U S A. 2015 Mar 3;112(9):2676-81. doi: 10.1073/pnas.1424549112. Epub 2015 Feb 17.
We report the observation of coherent circulation in a macroscopic Bose-Einstein condensate of polaritons in a ring geometry. Because they are spinor condensates, half-quanta are allowed in where there is a phase rotation of π in connection with a polarization vector rotation of π around a closed path. This half-quantum behavior is clearly seen in the experimental observations of the polarization rotation around the ring. In our ring geometry, the half-quantum state that we see is one in which the handedness of the spin flips from one side of the ring to the other side in addition to the rotation of the linear polarization component; such a state is allowed in a ring geometry but will not occur in a simply connected geometry. This state is lower in energy than a half-quantum state with no change of the spin direction and corresponds to a superposition of two different elementary half-quantum states. The direction of circulation of the flow around the ring fluctuates randomly between clockwise and counterclockwise from one shot to the next; this fluctuation corresponds to spontaneous breaking of time-reversal symmetry in the system. This type of macroscopic polariton ring condensate allows for the possibility of direct control of the circulation to excite higher quantized states and the creation of Josephson junction tunneling barriers.
我们报告了在环形几何结构中宏观极化激元玻色 - 爱因斯坦凝聚体中相干环流的观测结果。由于它们是自旋凝聚体，在围绕闭合路径的极化矢量旋转π导致相位旋转π的情况下，允许存在半量子。这种半量子行为在围绕环的极化旋转的实验观测中清晰可见。在我们的环形几何结构中，我们所看到的半量子态是这样一种状态，除了线性极化分量的旋转外，自旋的手性从环的一侧翻转到另一侧；这种状态在环形几何结构中是允许的，但在单连通几何结构中不会出现。这种状态的能量低于自旋方向不变的半量子态，并且对应于两个不同的基本半量子态的叠加。从一次测量到下一次测量，围绕环的流动的环流方向在顺时针和逆时针之间随机波动；这种波动对应于系统中时间反演对称性的自发破缺。这种类型的宏观极化激元环凝聚体使得直接控制环流以激发更高量子化态以及创建约瑟夫森结隧穿势垒成为可能。
