Thursday, June 27, 2024

16:00 - 17:00

Precision spectroscopy with lasers of atoms and molecules is widely used for tests of elements of the Standard Model of physics (such as quantum electrodynamics), and for determinations of fundamental constants and nuclear charge radii. This requires ‘simple’ systems that can be calculated accurately. In the talk I will focus on our precision measurements in helium, were we first (laser) cool 3He (a fermion) and 4He (a boson) to quantum degeneracy and ultimately trap them in a focused laser beam at the ‘magic’ wavelength of 320 nm. Of both trapped and ultra cold isotopes we measure the doubly-forbidden 2 3S1 – 2 1S0 transition frequency at 1557 nm with twelve digits. For the difference in transition frequency (the isotope shift), the biggest theoretical uncertainty is due to the uncertainty of the nuclear charge radius of both isotopes. Therefore we can use our measurement to deduce a charge radius (squared) difference between the helion and alpha particle with unprecedented accuracy [1]. Interestingly, an evaluation recently by the CREMA collaboration of the same charge radius difference from muonic helium ion spectroscopy [2] leads to a value that deviates by 3.6 combined sigma from our measurement.

In the talk he will give special attention to the remarkable difference in quantum behaviour between 3He and 4He, and the consequences for cooling to ultra-low temperatures and the spectroscopy we perform.

[1] Y. van der Werf et al., arXiv:2306.02333

[2] K. Schuhmann et al., arXiv:2305.11679

Science Park 904

L1.02

Colloquium

quantum computing, quantum gases and quantum information, quantum matter

Prof. Dr. Kjeld Eikema