Towards a YbF MOT to measure the electron’s electric dipole moment.
Jorge Mellado-Munoz
Centre for Cold Matter, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ UK
The excess of matter in the universe cannot be explained by the Standard Model CP-violation, implying the existence of new physics. Some of the theoretical models that could solve this propose the existence of an electron electric dipole moment (eEDM) of de > 10−32 e · cm. In contrast, the eEDM predicted by the Standard Model is at most de < 10−38 e · cm. The most precise eEDM measurements have been made using polar molecules, exploiting the huge enhancement of electric field in these molecules, and the current best eEDM limit (|de| < 1.1 · 10−29 e · cm) was obtained using a beam of ThO molecules [1]. To improve on this, we propose to use ultracold molecules trapped in an optical lattice, in particular, YbF molecules. That is because these molecules have high eEDM sensitivity [2] and can be laser cooled to low temperature [3] so that they can be trapped in a lattice [4]. In this talk, I will discuss our recent progress towards this ambitious goal. The first step towards confining molecules in an optical lattice is to trap them in a magneto-optical trap (MOT). This is significantly more challenging than a MOT for atoms. We developed a cryogenic source that produces a cold molecular beam at 1.8K with slow forward velocity using the buffer-gas cooling technique. We are currently working on radiation pressure slowing of the molecules to achieve a forward velocity below the capture velocity of the MOT. Lastly, I will discuss our efforts on investigating small leaks out of the cooling cycle and how to close them [5].
References
[1] Andreev, V. et al. ”Improved limit on the electric dipole moment of the electron.” Nature 562 (2018): 355-360.
[2] Hudson, J. J., et al. ”Improved measurement of the shape of the electron.” Nature 473 (2011): 493-496.
[3] Lim, J., et al. ”Laser cooled YbF molecules for measuring the electron’s electric dipole moment.” Physical review letters 120 (2018): 123201.
[4] Fitch, N. J., et al. ”Methods for measuring the electron’s electric dipole moment using ultracold YbF molecules.” Quantum Science and Technology 6 (2020): 014006. [5] Zhang, Chi, et al. ”Inner-shell excitation in the YbF molecule and its impact on laser cooling.” Journal of Molecular Spectroscopy 386 (2022): 111625.