Difference Casimir Force Precision Measurements To Probe Long Wavelength Behavior

点击翻译按钮获取中文摘要

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.