Helium dimer Ultracold Molecules - a platform for fundamental physics and ultracold chemistry

Laser cooling of atoms has revolutionized physics and allowed studying nature with unprecedented sensitivity, precision and accuracy.

With their additional degrees of freedom, ultracold molecules offer even more.However, reaching high densities and a high number of elastic collisions are the two major challenges remaining to achieve quantum degeneracy with molecules. 4 molecules were laser cooled and trapped in the last decade, but recent experiments have shown universal loss upon collisions caused by the formation of complexes and therefore preventing further cooling.

Although not yet fully understood, the loss is favored by the large state densities of the heavy diatomic molecules used so far.I propose a novel strategy: HeliUM aims to overcome both obstacles by achieving direct laser cooling of the lightest and first homonuclear molecule He2 and establishing a path towards quantum degeneracy.

The light mass of the molecule, absence of hyperfine structure and a restricted set of rotational states due to the Pauli principle, drastically reduce the level density and facilitate evaporative cooling.

Additionally, relying on a continuous molecular beam and implementing an innovative slowing technique will lead to densities several orders of magnitude larger than in existing experiments.With HeliUM, I will provide a controllable, simple 4-electron system at record low temperature, allowing quantum sensing and precision measurements to test quantum physics and the quantum nature of collisions with unprecedented accuracy - while being accessible to highly accurate ab initio computational methods.By using Rydberg states and photodissociation, HeliUM will put me at the forefront of measuring cross sections for a plethora of reactions involving charged and neutral, atomic and molecular helium species, relevant for understanding He droplets, astro- and plasma physics.

This will complement my strong track record in precision measurements of molecular hydrogen and its ion.