Precision measurements of the gradient of the Casimir force between ultra clean metallic surfaces at larger separations

TL;DR

This study provides highly precise measurements of the Casimir force gradient between ultra-clean metallic surfaces at larger separations, challenging some theoretical models and confirming others, thus advancing understanding of quantum electromagnetic interactions.

Contribution

It offers new experimental data at larger distances and compares these with theoretical models, excluding the dissipative Drude model and confirming the plasma model's validity.

Findings

Dissipative Drude model is experimentally excluded from 250 to 1100nm.

Dissipationless plasma model agrees with measurements from 250 to 1300nm.

Enhanced measurement techniques enabled data collection at larger separations.

Abstract

We report precision measurements of the Casimir interaction at larger separation distances between the Au-coated surfaces of a sphere and a plate in ultrahigh vacuum using a much softer cantilever of the dynamic atomic force microscope-based setup and two-step cleaning procedure of the vacuum chamber and test body surfaces by means of UV light and Ar-ion bombardment. Compared to the previously performed experiment, two more measurement sets for the gradient of the Casimir force are provided which confirmed and slightly improved the results. Next, additional measurements have been performed with a factor of two larger oscillation amplitude of the cantilever. This allowed obtaining meaningful results at much larger separation distances. The comparison of the measurement data with theoretical predictions of the Lifshitz theory using the dissipative Drude model to describe the response of Au to the low-frequency electromagnetic field fluctuations shows that this theoretical approach is experimentally excluded over the distances from 250 to 1100nm (i.e., a major step forward has been made as compared to the previous work where it was excluded up to only 820nm). The theoretical approach using the dissipationless plasma model at low frequencies is shown to be consistent with the data over the entire measurement range from 250 to 1300nm. The possibilities to explain these puzzling results are discussed.