Coherence Control of Weak Localization in Cold Atoms

近年来，科学家们已经微调了他们的能力，将一些原子和分子的温度降低到接近绝对零度的开尔文温标。冷却到这个水平的原子，通常被称为“超冷”原子，其行为与室温下的原子不同，特别是在与激光相互作用时。甚至有可能使用激光将原子固定在适当的位置，以对抗重力。这样的原子被称为“被捕获的”。被捕获的原子可以作为基础科学研究的一部分进行研究，也可以用于现实世界的应用，比如建造非常精确的传感器，甚至可以部署在被称为“量子计算机”的新型计算机上。与激光相互作用的被困原子也可以用来模拟其他物理系统，例如，电子如何在固体中运动。这个项目探索了激光，其颜色是精心控制的，如何从被困的超冷原子系综中散射。该项目的实验目标有两个：1）在以前没有探索过的条件下研究激光散射，以更好地理解基本光散射动力学的复杂细节，以及2）使用附加的激光器来实际控制光散射过程-不仅仅是观察它。伴随着实验室中的这些实验，将努力完善对所有观察到的物理现象的理论理解，以便研究结果可应用于其他基础科学和应用研究问题。该项目旨在研究弱无序超冷原子气体中光散射和传输的未开发领域。特别是，相干后向散射（CBS），有时被称为“弱本地化”的干扰效应，在向后的方向上的光的散射增强的结果，将结合电磁诱导的类相干条件进行研究，探索潜在的控制方面的光散射过程。CBS效应的修正将被测量，使用光偏振，施加的磁场和原子密度作为主要的“控制旋钮”。在一个相关的项目中，CBS效应将在激光从原子跃迁偏离共振，并具有可变偏振和施加磁场时进行研究。在这里，一种被称为“反定位”的效应，由随着时间的推移而建立的超精细相干性引起，理论上预测会减少观察到的CBS信号。除了观察这种现象，特别感兴趣的是测量的失谐依赖的过程中，使比较理论预测和验证散射模型，在这regime.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

In recent years, scientists have fine-tuned their ability to lower the temperature of some atoms and molecules to close to absolute zero on the Kelvin temperature scale. Atoms cooled down to this level, often referred to as “ultracold” atoms, behave differently than atoms at room temperature, especially when interacting with laser light. It is even possible to use laser light to hold atoms in place, countering the force of gravity. Such atoms are referred to as “trapped.” Trapped atoms can be studied as part of fundamental science investigations or used for real-world applications, like building very precise sensors or even deployed for a new class of computers known as “quantum computers.” Trapped atoms interacting with laser light can also be used to model other physical systems, for example, how electrons might travel in solids. This project explores how laser light, whose color is carefully controlled, scatters off of an ensemble of trapped, ultracold atoms. The experimental objectives of this project are twofold: 1) to study laser light scattering under conditions that have not been explored before to better understand the intricate details of the fundamental light scattering dynamics, and 2) to use additional lasers to actually control the light scattering process – not just to observe it. Accompanying these experiments in the laboratory will be an effort to refine the theoretical understanding of all of the observed physical phenomena so that the findings can be applied to other basic scientific and applied research problems. The project is directed towards investigation of unexplored areas of light scattering and transport in weakly disordered, ultracold atomic gases. In particular, coherent backscattering (CBS), an interference effect sometimes referred to as “weak-localization,” that results in enhanced scattering of light in the backwards direction, will be investigated in conjunction with electromagnetically-induced transparency-like conditions to explore potential control aspects to the light scattering process. Modification to the CBS effect will be measured, using light polarization, applied magnetic fields and atomic density as the principal “control knobs.” In a related project, the CBS effect will be investigated when the laser light is off-resonance from an atomic transition, and with variable polarization and applied magnetic fields. Here, an effect known as “anti-localization,” arising from hyperfine coherences that build up over time, is predicted – theoretically - to reduce the observed CBS signal. Beyond observation of this phenomena, of particular interest is measurement of the detuning dependence of the process to enable comparison to theoretical predictions and validate scattering models in this regime.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.