Advances in Casimir-Polder Interactions Between Atoms and Substrates

微妙的量子力学效应可以在物体之间产生不寻常的力。例如，与电场和磁场波动相关的量子不确定性可以在分子之间或分子与表面之间产生不寻常的力。这些效应，通常被称为卡西米尔相互作用，很久以前就被发现了，并被认为在宏观物体之间产生非常微小的力。它们现在被认为对纳米大小的物体，如纳米机器和大分子，尤其重要，因此成为传感器技术和精密测量物理学研究的焦点。从第一性原理精确计算卡西米尔力是一项艰巨的挑战，因为它涉及到波动场的精细平均，会产生奇怪的结果；这些力可以是吸引的，也可以是排斥的，可以增加或减少系统的熵。这个项目将通过对当前实验感兴趣的系统进行明确的计算，增强我们对卡西米尔力的理解。本研究成果在化学、生物学、纳米科学、原子物理和核物理等领域均有应用。这项工作正在与世界各地的研究人员合作进行，包括资深科学家、博士后、研究生、本科生和高中生。该项目旨在提高我们对零温度和有限温度下卡西米尔（量子涨落）能量和力的理解，例如，通过使用格林函数和其他分析技术来计算原子球形模型的卡西米尔自熵。这需要隔离、调节和重新规范化自由能，这些过程也必须对与量子场相关的能量进行处理，无论是平面还是曲面的外部还是内部。最近发现，一个完全导电的球体和一个完全导电的板之间相互作用的负熵恰好被球体的正自熵所平衡。负熵与排斥力不无关系，排斥力可以在真空中的原子和其他物体之间实现。卡西米尔力的不可加性在这些现象中起着重要的作用。虽然这一领域的大部分工作都集中在物体之间的法向力，但也在探索横向力，以及卡西米尔扭矩和卡西米尔摩擦，希望后两种现象可以很快在实验室实验中看到。研究人员正在与一个由学生和高级研究人员组成的不同国际小组合作，研究其应用，如表面冰的冻结，以及磷烯等新材料的性能。

Subtle quantum mechanical effects can produce unusual forces between objects. The quantum uncertainty associated with electric and magnetic field fluctuations, for example, can produce unusual forces between molecules, or between molecules and surfaces. These effects, generally known as Casimir interactions, were discovered long ago and thought to generate very tiny forces between macroscopic objects. They are now understood to be especially important for nanometer-sized objects, such as nano-machines and macro-molecules, and so are becoming the focus of much research on sensor technology and precision measurement physics. Accurate calculation of Casimir forces from first principles is a difficult challenge, as it involves delicate averaging of fluctuating fields, with strange consequences; the forces can be either attractive or repulsive, and can either contribute to or detract from the system's entropy. This project will enhance our understanding of Casimir forces through explicit calculations focused on systems of current experimental interest. Results of this research have applications to chemistry, biology, nanoscience, and atomic and nuclear physics. This work is being carried out in collaboration with researchers world-wide, including senior scientists, postdocs, graduate students, undergraduate students, and high-school students.This project seeks to advance our understanding of Casimir (quantum-fluctuation) energies and forces at zero and finite temperatures, for example, by using Green's function and other analytic techniques to compute Casimir self-entropies for a spherical model of an atom. This requires isolating, regulating, and renormalizing the free energy, processes that also have to be done for the energy associated with quantum fields external and internal to surfaces, either flat or curved. It has recently been discovered that the negative entropy of interaction between a perfectly conducting sphere and a perfectly conducting plate is exactly balanced by the positive self-entropy of the sphere. Negative entropies are not unrelated to repulsive forces, which can be realized between atoms and other bodies in vacuum. The nonadditivity of Casimir forces plays an important role in these phenomena. Although most work in this field has concentrated on the normal force between bodies, lateral forces are also being explored, along with Casimir torque and Casimir friction, with the hope that these latter two phenomena may be soon seen in laboratory experiments. Applications, such as to the freezing of ice on surfaces, and properties of new materials such as phosphorene, are being studied in collaboration with a diverse international group of students and advanced researchers.