Control of the Casimir force by the modification of dielectric properties with light

Abstract

The experimental demonstration of the modification of the Casimir force between a gold coated sphere and a single-crystal Si membrane by light pulses is performed. The specially designed and fabricated Si membrane was irradiated with 514 nm laser pulses of 5 ms width in high vacuum leading to a change of the charge-carrier density. The difference in the Casimir force in the presence and in the absence of laser radiation was measured by means of an atomic force microscope as a function of separation at different powers of the absorbed light. The total experimental error of the measured force differences at a separation of 100 nm varies from 10 to 20% in different measurements. The experimental results are compared with theoretical computations using the Lifshitz theory at both zero and laboratory temperatures. The total theoretical error determined mostly by the uncertainty in the concentration of charge carriers when the light is incident is found to be about 14% at separations less than 140 nm. The experimental data are consistent with the Lifshitz theory at laboratory temperature, if the static dielectric permittivity of high-resistivity Si in the absence of light is assumed to be finite. If the dc conductivity of high-resistivity Si in the absence of light is included into the model of dielectric response, the Lifshitz theory at nonzero temperature is shown to be experimentally inconsistent at 95% confidence. The demonstrated phenomenon of the modification of the Casimir force through a change of the charge-carrier density is topical for applications of the Lifshitz theory to real materials in fields ranging from nanotechnology and condensed matter physics to the theory of fundamental interactions.

Modifying the Casimir force between indium tin oxide film and Au sphere

“…First, we briefly consider the preparation of the sphere which was done similar to previous experiments. [20][21][22]27,28,39,40,43,44 We used a polystyrene sphere which was glued with silver epoxy (20 × 20 µm 2 spot) to the tip of a triangular silicon nitride cantilever with a nominal spring constant of order 0.01 N/m. The cantilever-sphere system was then coated with a 10 nm Cr layer followed by 20 nm Al layer and finally with a 105 ± 1 nm Au layer.…”

“…26 Keeping in mind the applications to micromachines, it is important to control both decreases and increases in the force magnitude. For this purpose, the difference in the Casimir force between a Si plate and an Au sphere was measured 27,28 in the presence and in the absence of 514 nm Ar laser light on the plate. The respective increase in magnitude of the Casimir force by a few percent was observed when the plate is illuminated with laser pulses.…”

“…27,28 When the charge carriers are taken into account, the Lifshitz theory is excluded by the data at a 95% confidence level. Similar results were obtained from the measurement 35 of the thermal Casimir-Polder force between 87 Rb atoms belonging to the Bose-Einstein condensate and a SiO 2 plate: theory is in agreement with the data when dc conductivity of the dielectric plate is disregarded, 35 but the same theory is excluded by the data at a 70% confidence level when dc conductivity is taken into account.…”

Constraints on non-Newtonian gravity and light elementary particles from measurements of the Casimir force by means of a dynamic atomic force microscope

“…For dielectric test bodies the theoretical predictions were found in agreement with the data only if the contribution of free charge carriers is omitted [33][34][35][36][37][38]. Keeping in mind that many of the experiments mentioned above were used, first, to make a selection between different theoretical approaches and, second, to constrain corrections to Newtonian gravity from the measure of agreement between the data and the predictions following from a selected approach, the constraints obtained were sometimes claimed to be of dubious merit [39].…”

How to modify the van der Waals and Casimir forces without change of the dielectric permittivity

“…In the optical modulation experiment [46,47], where a Si plate was radiated with laser pulses, the free charge carrier density n fc in the absence of a pulse was much smaller than the critical concentration at which Si becomes metallic. As a result, the contributions of free charge carriers in the absence and in the presence of laser light were quite different.…”