Ultracold YbCr: A new generation platform to probe charge-parity violating physics beyond the Standard Model

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 (SM). The detection of an electric dipole moment (EDM) of a fundamental particle would directly signal CP violation beyond the SM and grant access to new physics. The current limit on the electron EDM (eEDM) is set by atomic and molecular optics experiments exploiting the giant electric field and unpaired electrons inside polar paramagnetic molecules. Molecules at ultracold temperatures are expected to provide several orders of magnitude gain in the eEDM sensitivity.

Based on a recent theoretical proposal in collaboration with the team of Prof. M. Tomza (Warsaw) [1], within the project COMPASS we will realize the first ultracold gas of eEDM-sensitive YbCr molecules, combining relativistic ytterbium (Yb) with high-spin chromium (Cr). This specific choice allows the production of large samples and long interrogation times, while granting strong field and an ideal internal structure within each molecule. I will show our experimental strategy and design of this new-generation platform.  The success of COMPASS will lead to order-of -magnitude gain in eEDM sensitivity via standard spin-precession measurements, with possible extension to more advanced metrology protocols.

[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)