Ultracold high-spin Σ-state polar molecules for new physics searches

The asymmetry between ordinary matter and antimatter represents one of the great mysteries in modern physics. One promising way to search for answers is to look for violations of fundamental symmetries (CP,T) beyond the Standard Model, such as a possible electric dipole moment of the electron. The current limit on the electron EDM is set by AMO experiments exploiting polar paramagnetic molecules. Remarkably, high-precision measurements in such low energy experiments, probe mass ranges of proposed CP-violating particles well beyond the direct reach of particle colliders. Molecules at ultracold temperatures are expected to provide several orders of magnitude gain in sensitivity, but the strategy to get there is yet unclear.

I will report on our recent theory proposal based on Σ-state polar molecules assembled from ultracold atoms [1]. I will explain how the combination of relativistic ytterbium and high-spin chromium, amenable to magnetoassociation, leads to molecules with easy-to-polarize parity doublets and large effective electric fields. Based on ab initio results for molecular constants, we predict a sensitivity of δde = (6 × 10⁻³¹/√n_day) e cm via standard spin-precession measurements, with potential extension to more advanced measurement protocols and searches in the hadronic sector. Finally, I will outline the experimental strategy and assess its feasibility.

[1] A. Ciamei, A. Koza, M. Gronowski, and M. Tomza, Ultracold high-spin Σ-state polar molecules for new physics searches, arXiv:2507.16760 (2025)