Speaker
Description
Precision measurements on calculable systems are widely used for tests of QED and probes for physics beyond the standard model. In our experiment we perform high precision spectroscopy on the $2\,^3S_1 – 2\,^1S_0$ transition at 1557 nm in ultracold $^3$He and $^4$He.
On this transition we recently performed the most accurate frequency measurement (48 Hz) in helium, using a Bose-Einstein condensate of $^4$He trapped in a magic wavelength optical dipole trap. To achieve the accuracy, we developed methods to observe and subsequently suppress systematic Doppler shifts from the BEC oscillating in the optical trap, and we referenced the experiment via a White Rabbit link to a remote hydrogen maser at VSL.
Combined with our previous measurement in $^3$He [1], and recent theory [2], we can determine the squared charge radius difference between the alpha and helion particle with unprecedented accuracy. Our result [2] is consistent with recent other determinations and confirms that the QED theory discrepancy seen in excited states of helium [4] is not apparent in the isotope shift.
[1]: Science 388, 850-853(2025)
[2]: Phys. Rev. A 113, 012824 (2026)
[3]: arXiv: 2601.19444 (2026)
[4]: Phys. Rev. Lett. 134, 223001 (2025)