Casimir-Polder interaction control of cold atoms and nano devices for fundamental physics

A striking feature of quantum mechanics is the possibility of energy change ∆E during a time ∆t due to the Heisenberg principle (∆E∆t≥ħ/2). It leads to quantum fluctuations that create virtual photons and generate a quantized field. In particular, the presence of boundaries, given for example by a surface and an atom, modifies this field. It results in a force between the surface and the atom, known as the Casimir-Polder (C-P) force. This force becomes preponderant at the nanoscale and thus plays a major role in a multitude of areas of Physics, ranging from atomic physic to theoretical fundamental physics such as the 5^th force and accurate gravity measurement.

Despite its simplicity, combined with strong scientific and technological interests, C-P interaction, at its fundamental level, remains largely unexplored mainly due to challenges associated with precise control of the atom-surface distance and knowledge of the surface characterization. In this context, our teamhas built a slow atomic beam interacting with a nanograting [1,2]. This jet interacts with a carefully self-engineered nanograting, leading to a diffraction pattern dominated by the C-P force. This unique configuration allows us to study precisely the C-P interaction.

**Figure**. Sketch of the team’s experiment, in which a cold atom source containing neutral Argon is optically pushed towards a nanograting. The atoms thereupon interact with the nanograting within the C.P potential, resulting in a diffraction pattern. A typical measured diffraction pattern is shown on the left in blue. The experimental signal is mainly influenced by the C.P interaction, as underlined by the expected diffraction pattern without the C.P potential shown in red. On the right is an image of typical manufactured nanogratings used in the experiment.

The current interest of the experiment is to achieve an in-depth understanding of the C-P interaction. To achieve this goal, the successful applicant will take an active role in various aspects of the experiment including data acquisition, data analysis, the development of tools for characterizing the atomic source, and the installation of an optical dipole trap (to increase the atomic flux and reduce the atomic velocity). Additionally, the internship has as well a theoretical component with the description of the interference figure and quantum electrodynamic calculations. According to the candidate’s preferences, there may also be a clean-room aspect to the internship, involving work on the generation of new nanogratings. The short term goal of the project is to tailor the C-P interaction using material geometries. In the medium term, this work will open the door to study eventual modifications of the Newtonian gravitational interaction at short range, where C-P interaction shields such forces.

The successful applicant will work as a fully integrated team member. The internship encompasses various components, including experimental work, cleaning room activities, and theoretical studies, which we can be arranged to suit the applicant’s preferences. The master’s internship is scheduled to begin in spring 2025, and it can be followed by a PhD thesis funded by ANR, starting in September 2025.

[1] C. Garcion, et al. Phys. Rev. Lett. 127, 170402 (2021).
[2] J. Lecoffre et al, arXiv:2407.14077 (2024).