# Examining the Casimir puzzle with upgraded technique and advanced surface cleaning

## TL;DR

This study improves measurement accuracy of the Casimir force gradient using upgraded AFM techniques and advanced surface cleaning, providing new insights into theoretical models and the foundations of quantum statistical physics.

## Contribution

It introduces an enhanced experimental setup with better cleaning and softer cantilevers, enabling more precise tests of Lifshitz theory and surface effects in Casimir force measurements.

## Key findings

- Relaxation-based Lifshitz theory is excluded by data up to 820 nm.
- Alternative theoretical approach shows very good agreement with measurements.
- Advanced cleaning reduces electrostatic patch effects and improves measurement accuracy.

## Abstract

We performed measurements of the gradient of the Casimir force between Au-coated surfaces of a sphere and a plate by means of significantly upgraded dynamic atomic force microscope (AFM) based technique. By introducing combined cleaning procedure of interior surfaces of the vacuum chamber and the test bodies by means of UV light and Ar ions, we reached higher vacuum and eliminated the role of electrostatic patches. Furthermore, the use of much softer cantilever allowed a sixfold decrease of the systematic error in measuring the force gradient. The experimental data are compared with theoretical predictions of the Lifshitz theory taking into account corrections due to the inaccuracy of the proximity force approximation and that due to surface roughness. It is shown that the theoretical approach accounting for the relaxation properties of free electrons is excluded by the data up to a larger than previous sphere-plate separation of 820~nm, whereas an alternative approach is found in a very good agreement with the data. Importance of these results in connection with the foundations of quantum statistical physics is discussed.