High Precision Casimir Force Measurements

根据量子理论，其许多预测现在已经被非常精确地验证，真空空间并不是空的，而是充满了粒子，如光子（光的粒子），它们在真空中进进出出，被称为虚光子或零点光子。 这些零点光子的存在已经在实验中得到了验证，例如测量“兰姆位移”的实验，兰姆位移是氢原子能级的一种微小但重要的位移（1955年诺贝尔奖）。 虚粒子不仅是物理学中深奥的概念，而且是生物生命和化学的核心，因为它们在货车德瓦尔斯力中发挥作用，这些力负责细胞壁的强度并决定蛋白质的优选结构，以及许多其他效应。 它们也对中性物体之间的摩擦力和粘附力起很大作用。 虽然虚光子的重要性是清楚的，但它们如何与真实的物体相互作用并导致这种力还没有完全理解。在这个项目中，主要研究人员通过比较卡西米尔力的精确测量和理论来直接研究这一点，卡西米尔力是货车德瓦尔斯力的宏观长距离版本，它预测了两个不带电的理想金属板之间的力。 卡西米尔力可以被认为是光子在反射时从板上反弹的净力，或者是由相同光子引起的电荷和电流波动的相互作用。如果也存在真实的光子，例如来自相互作用物体的热光子发射，它们将以相同的方式对卡西米尔力做出贡献。其中一个最基本的问题是零点光子如何与真实的物质相互作用，以及这种相互作用是否与真实的光子的相互作用不同。首先，它必须在净能量吸收方面有所不同。真实的光子与所有材料相互作用以传递能量和热量（例如，加热留在太阳下的物体）。 但是零点光子不能做同样的事情，因为那会导致能量的净创造。该项目将通过对不同材料和不同温度下的卡西米尔力进行精确测量来寻找真实的和零点光子之间的潜在差异。 不同的材料具有不同的反射，因此具有不同的卡西米尔力。而且，所有材料在非零温度下发射真实的光子，这可能与它们的温度和材料性质有关。通过使用不同的材料，主要研究人员将改变真实的光子对零点光子的贡献率，从而能够梳理出它们相互作用的任何差异。科学影响是对零点光子性质的基本理解。技术影响将体现在新型微机电（MEM）器件的设计中。 由于卡西米尔力在亚微米尺度特征的MEMS中超过了正常的电磁和引力效应，因此有真实的需要理解这些效应。在室温和小于1微米的板分离下，卡西米尔力绝大多数来自零点光子。 由于普朗克热发射光谱的峰值约为7微米，因此人们直观地预期，随着分离的增加，额外的热光子贡献增加了力，但随着材料吸收，热光子贡献令人惊讶地排斥高达6微米。 两个物体在不同温度下的情况是迷人的，因为力可以是排斥力，振荡力或零。在这种情况下，关键的贡献是来自近场热发射，这是许多数量级大于预期的普朗克热发射光谱。 主要研究人员还将开发一种新的实验配置，以提高实验的精度：而不是使用两个板，球板布置将用于避免保持两个板完全平行的问题。将使用两种方法：（i）通过悬臂的谐振频率偏移测量卡西米尔力梯度;以及（ii）使用周期性图案化的深沟槽在表面和真空之间进行差分卡西米尔力测量，所述深沟槽驱动悬臂以大幅度谐振，然后可以检测到所述大幅度谐振。 测量的力将被比较到相关的不同的实验配置，以了解零点和热光子的作用的发展散射理论。

According to quantum theories, whose many predictions have now been verified with great precision, empty space is not empty but is teeming with particles such as photons (particles of light) which pop into and out of the vacuum and are referred to as virtual photons or zero point photons. The presence of these zero point photons has been verified in experiments such as those which measure the "Lamb shift," a small but significant shift in the energy levels of hydrogen atoms (Nobel Prize 1955). Virtual particles are not just concepts of esoteric interest to physics but are central to biological life and chemistry as they play a role in the van der Waals forces that are responsible for the strength of cell walls and determine the preferred structure of proteins, among many other effects. They also contribute to a large component of the frictional and adhesive forces between neutral objects. While the importance of the virtual photons is clear, exactly how they interact with real objects and lead to such forces is not fully understood. In this project the principal investigators study this directly by comparing precision measurements and theory of the Casimir force, the macroscopic long distance version of the van der Waals force which predicts a force between two uncharged ideal metal plates placed in empty space. The Casimir force can be thought of as the net force from the photons bouncing off the plates on reflection or as an interaction of the charge and current fluctuations induced by the same photons. If real photons such as the thermal photon emission from the interacting objects are also present, they will contribute to the Casimir force in the same manner. One of the most basic questions is how zero point photons interact with real material objects and whether the interaction is different from that of real photons. For one, it has to be different with regard to the net energy absorption. Real photons interact with all materials to transfer energy and heat (for example, heating of an object left in the sun). But zero point photons cannot do the same, as that would lead to a net creation of energy. This project will look for potential differences between real and zero point photons by performing precision measurements of the Casimir force with different materials and at different temperatures. Different materials have different reflections and thus different Casimir forces. Also all materials at non-zero temperature emit real photons which can be related to their temperature and material properties. By using different materials, the principal investigators will vary the ratio of contribution of the real photons to the zero point photons and thus be able to tease out any differences in their interaction. The scientific impact is a fundamental understanding of the nature of zero point photons. The technological impact will be in the design of novel micro electromechanical (MEM) devices. As the Casimir force exceeds normal electromagnetic and gravitational effects in MEMs operating with submicron scale features, there is a real need to understand these effects.At room temperature and plate separations below 1 micron, the Casimir force comes overwhelmingly from zero point photons. As the peak of the Planck thermal emission spectrum is around 7 microns, one intuitively expects that the additional thermal photon contribution adds to the force as separation increases, but with material absorption, the thermal photon contribution is surprisingly repulsive up to 6 microns. The case of two objects at different temperatures is fascinating, as the force can be repulsive, oscillatory or zero. In this case the critical contribution is from the near-field thermal emission, which is many orders of magnitude larger than that expected from the Planck thermal emission spectrum. The principal investigators will also develop a new experimental configuration to improve the precision of the experiments: instead of using two plates, a sphere-plate arrangement will be used to avoid issues with keeping two plates perfectly parallel. Two methods will be used: (i) measurement of the Casimir force gradient through the resonance frequency shift of a cantilever; and (ii) difference Casimir force measurement between a surface and vacuum using periodically patterned deep trenches which drive a cantilever into resonance with a large amplitude which can then be detected. Measured forces will be compared to the developed scattering theories relevant to the different experimental configurations to understand the roles of the zero point and thermal photons.