Parallel-Plate Casimir Force Experiments

Being one of the few known quantum effects acting on the macro scale, the Casimir effect has attracted great attention since its discovery in 1948. Despite this fact, an experimental verification required the application of modern laboratory equipment and was only achieved half a century later. Since then, the effect has been assessed and verified experimentally for various different geometric configurations, and agreement with theoretical predictions has been achieved to far below one percent of the measured values. Most experiments conducted to this point are being based on the geometry of a sphere over a plate which circumvents the problem of maintaining parallelity. However, this also introduces a source of error since a theoretical description is only possible within the so called proximity force approximation. In the literature there is a long standing controversy about possible theoretical approaches to describe thermal corrections to the Casimir effect. Precision measurements at short distances have already been utilized to exclude the Drude model in this respect. A definite answer to this problem could only be given by an experiment being conducted at large distances (greater than 1 &mikro;m) since in this regime thermal effects accounts for more than 50% of the force. However, such measurements generally exhibit rather large error levels due to the extremely low amplitude of the net signal. A possible solution could be to utilize large plates to up-scale the force. In this way error levels of below 10 % at distances above 4 &mikro;m should be achievable which would allow for definite evidence regarding thermal corrections. Another interesting effect at the micro scale is the transition from classical no-slip behavior to almost perfect slipping at fluid-solid interfaces for small distances between the confining walls. This phenomenon is not completely understood and has been investigated recently using an atomic force microscope (AFM) setup similar to the one utilized in Casimir experiments. It has also been shown that, when measuring quantum mechanical forces under ambient conditions, it is important to consider hydrodynamical forces in the analysis. Again, parallel plates could help to achieve more precise measurements of the effect since they allow to approximately resemble the assumption of infinitely extended flat surfaces which is often taken in the solution of the Navier Stokes equation. It is proposed to develop an experiment based on AFM techniques with parallel plates to measure either of the effects mentioned above at high precision. Advanced feedback mechanisms which have already been demonstrated in the literature shall be applied to remedy the problem of maintaining parallelity below 1 mrad relative misalignment. Established dynamic calibration and measurement techniques shall be utilized to allow for unambiguous experimental evidence regarding thermal corrections to the Casimir effect. Designing the setup to be capable of exchanging the medium confined between the plates by any fluid or gas, a detailed investigation of the transition from no-slip to perfect slip behavior from several &mikro;m down to 100 nm will be conducted. The apparatus being constructed during the proposed project could serve as a universal platform for several distinct future experiments. In addition, the experience gained by the applicant would be applicable in various ways to nanotechnology and fills a white spot on the scientific map in Austria - Casimir physics.