Difference Casimir Force Precision Measurements To Probe Long Wavelength Behavior

根据物理学的量子理论（包括普朗克黑体辐射定律和海森堡测不准原理），真空并不是真正的空无一物，而是充满了零点能量或量子涨落。这可能与海森堡测不准原理有关，在真空中，平均能量必须为零，但在短时间内，能量波动可能是非零的。对于电磁力，这种波动被称为零点（或“虚”）光子（光子是光的粒子）。这些零点光子的存在已经被获得诺贝尔奖的实验最终证实。物理边界的存在（例如通过放置反射光的镜子）导致虚拟光子允许频率的改变，这被称为卡西米尔效应。由改变边界（即镜面）分离引起的零点光子能量的变化产生一种称为卡西米尔力的力。零点光子产生的力（例如所谓的“范德华力”）是许多科学领域的核心，在化学分子结构、蛋白质结构和细胞生物学中起着关键作用。此外，由于卡西米尔力在具有亚微米距离运动部件的微机械装置中超过了正常的电磁和引力效应，因此有实际需要了解这些效应。为了更好地理解和控制这些效应，该项目正在定量研究这些效应在各种几何结构和温度下的性质。这项工作是在一所西班牙裔服务机构为各种各样的学生提供教育机会。这个项目的目标是了解零点光子与真实材料的相互作用。非零温度下的卡西米尔力既可以由零点光子产生，也可以由普朗克黑体热光子（实光子）产生。对实际金属板的卡西米尔力的推广适用于零点和实际光子相互作用的相同方法。它基于涨落耗散定理，其中边界上的电磁涨落与介电常数虚项的耗散直接相关。实验精度的提高突出了与理论的分歧，特别是在1.0微米以下的表面分离。由此产生的问题是：零点光子与材料的相互作用是否与真实光子的相互作用相同？关键的区别是：(i)零点光子不能在相互作用中传递净能量，例如在焦耳加热中光子与材料的实际相互作用的情况，以及（ii）零点光子不能同时保持能量-动量关系（ω≠kc），因为它们是海森堡涨落，不在“质量壳层上”。对卡西米尔力起主要作用的光子波长与边界分离是有序的。在室温和平板间距为1微米时，卡西米尔力绝大多数来自零点光子。由于普朗克热光谱的峰值在室温（300 K）下的波长为7.6微米，因此人们直观地认为，随着分离的增加，额外的热（实）光子贡献会增加力。奇怪的是，在包含耗散的情况下，热光子的贡献在6微米以内是排斥性的。在这个项目中，为了了解零点光子和热光子的长波贡献，将尝试在高达5微米的距离处进行精确的差分卡西米尔力测量。将尝试通过实验来研究它们的共同贡献，并通过筛选零点光子的贡献来隔离热光子的贡献。通过使用不同的材料和不同的温度，进行这个项目的科学家将改变零点光子和热光子贡献的比例。而不是两个板，球板的安排避免了保持板完全平行的问题。卡西米尔力的差异将在一个周期性图案的金板和金球之间进行测量。周期性的卡西米尔力将驱动附着在球体上的悬臂梁产生共振，其振幅很大，可以用锁相测量。图案板在球体下旋转或线性平移。实验数据将与已开发的实验配置的精确理论进行比较。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

According to the quantum theory of physics (which includes Planck black body radiation law and the Heisenberg uncertainty principle) empty space is not truly empty but is filled with zero point energy or quantum fluctuations. This can be related to the Heisenberg uncertainty principle, where in empty space the average energy has to be zero, but one can have non-zero energy fluctuations for short periods of time. For the electromagnetic force such fluctuations are referred to as zero point (or "virtual") photons (photons being particles of light). The existence of these zero point photons has been conclusively verified by Nobel Prize winning experiments. The presence of physical boundaries (for example by placing mirrors which reflect the light) leads to modifications of the allowed frequencies of the virtual photons and is referred to as the Casimir Effect. The change in the zero point photon energy caused by changing the boundary (i.e mirror) separation results in a force called the Casimir force. Forces resulting from zero point photons (e.g. the so-call "van der Waals forces") are central to many fields of science and play a critical role in molecular structure in chemistry, protein structure, and cell biology. In addition, because the Casimir force exceeds normal electromagnetic and gravitational effects in micromechanical devices with moving parts at submicron separations, there is a practical need to understand these effects. This project is quantitatively investigating the nature of these effects under a variety of geometrical configurations and temperatures in order to better understand and control them. The work is providing educational opportunities for a diverse range of students at a Hispanic-serving institution.The objective of this project is to understand zero point photon interaction with real materials. The Casimir force at non-zero temperature can arise from zero point photons as well as Planck black body thermal photons (real photons). Generalizations of the Casimir force for real metal plates follow the same approach for both zero point and real photon interactions. It is based on the fluctuation dissipation theorem where the electromagnetic fluctuations on the boundary are directly related to the dissipation from the imaginary term of the permittivity. Improvements in experimental precision have highlighted disagreements with the theory particularly for surface separations below 1.0 micron. The question that arises is: Are zero point photon interactions with materials the same as real photon interactions? The key differences are: (i) zero point photons cannot transfer net energy on interactions such as the case in Joule heating for real photon interactions with materials, and (ii) zero point photons do not simultaneously conserve energy-momentum relations (ω≠ kc) as they are Heisenberg fluctuations which are not "on the mass shell”. The photon wavelengths that primarily contribute to the Casimir force are of order the boundary separations. At room temperature and plate separations ~ 1 micron, the Casimir force comes overwhelmingly from zero point photons. As the peak of the Planck thermal spectrum is at a wavelength of 7.6 microns at room temperature (300 K), one intuitively expects that the additional thermal (real) photon contributions add to the force as the separation increases. Strangely, with the inclusion of dissipation, the thermal photon contribution is repulsive up to 6 microns. In this project, precision difference Casimir force measurements at separations up to 5 microns will be attempted in order to understand the long wavelength contributions of the zero point and thermal photons. Experiments to study their contribution together and by isolating the thermal photon contribution by screening out the zero point photon contribution will be attempted. By using different materials and different temperatures the scientists carrying out this project will vary the ratio of the zero point and thermal photon contributions. Instead of two plates, a sphere-plate arrangement avoids issues with keeping the plates perfectly parallel. The difference Casimir force will be measured between a periodically patterned gold plate and gold sphere. The periodic Casimir force will drive the cantilever attached to the sphere into resonance with a large amplitude which is measured with a lock-in. The patterned plate is either rotated or linearly translated under the sphere. The experimental data will be compared to the developed exact theories for the experimental configurations.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.