冷原子穿越单向势垒的动力学
Dynamics of Cold Atoms Crossing a One-Way Barrier
摘要：
我们实现了一个光学单向势垒，允许超冷的$^{87}$ Rb原子透射时，入射到势垒的一侧，但从其他反射。这种不对称势垒是麦克斯韦恶魔的实现，它可以用来产生相空间压缩，并对冷却不适合标准激光冷却技术的原子和分子产生影响。屏障包括两个聚焦的高斯激光束，它们与保持原子的远场共振单光束光学偶极阱的焦点相交。主势垒光束对入射原子呈现一个依赖于态的势，而再泵浦势垒光束则将原子光学泵浦到一个陷阱态。我们研究了势垒不对称性对势垒光束间距、初始原子势能、第二光束强度和第一光束失谐量变化的鲁棒性。我们进行了模拟的原子动力学中存在的障碍，表明初始的三维动量分布起着重要的作用，光辅助碰撞可能是占主导地位的损失机制。我们还仔细检查了与麦克斯韦恶魔的关系，并明确说明了我们特定系统的熵的明显减少。
英文摘要：
We implemented an optical one-way potential barrier that allows ultracold $^{87}$Rb atoms to transmit through when incident on one side of the barrier but reflect from the other. This asymmetric barrier is a realization of Maxwell's demon, which can be employed to produce phase-space compression and has implications for cooling atoms and molecules not amenable to standard laser-cooling techniques. The barrier comprises two focused, Gaussian laser beams that intersect the focus of a far-off-resonant, single-beam optical dipole trap that holds the atoms. The main barrier beam presents a state-dependent potential to incident atoms, while the repumping barrier beam optically pumps atoms to a trapped state. We investigated the robustness of the barrier asymmetry to changes in the barrier beam separation, the initial atomic potential energy, the intensity of the second beam, and the detuning of the first beam. We performed simulations of the atomic dynamics in the presence of the barrier, showing that the initial three dimensional momentum distribution plays a significant role, and that light-assisted collisions are likely the dominant loss mechanism. We also carefully examined the relationship to Maxwell's demon and explicitly accounted for the apparent decrease in entropy for our particular system.
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