Coherence Control of Weak Localization in Cold Atoms

近年来，科学家们微调了他们的能力，将一些原子和分子的温度降低到接近开尔文温标的绝对零度。冷却到这一水平的原子，通常被称为“超冷”原子，在室温下的行为与原子不同，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，以抵消重力。这样的原子被称为“陷阱”。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，甚至可以部署到一种被称为“量子计算机”的新型计算机中。被捕获的原子与激光相互作用也可以用来模拟其他物理系统，例如，电子如何在固体中传播。这个项目探索了激光是如何从一组被捕获的超冷原子中散射出来的，激光的颜色是被仔细控制的。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，以更好地了解基本光散射动力学的复杂细节；2)使用额外的激光来实际控制光散射过程--而不仅仅是观察它。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，以便这些发现可以应用于其他基本的科学和应用研究问题。该项目旨在调查弱无序、超冷原子气体中的光散射和传输的未探索区域。特别是，相干后向散射(CBS)，一种有时被称为“弱局部化”的干扰效应，导致光在向后方向上的增强散射，将与电磁诱导的类似透明的条件一起被研究，以探索光散射过程的潜在控制方面。对CBS效应的修正将被测量，使用光偏振、外加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，将研究当激光偏离原子跃迁的共振时，在可变偏振和外加磁场的情况下的CBS效应。在这里，理论上预测，随着时间的推移，超精细相干产生的“反局部化”效应将减少观测到的CBS信号。除了对这种现象的观察之外，特别感兴趣的是测量该过程的失谐依赖性，以便能够与理论预测进行比较，并验证该方案中的散射模型。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.