An ultracold Molecule Platform for fundamental Asymmetry Searches

The asymmetry between ordinary matter and antimatter represents one of the great mysteries in modern physics. Proposed baryogenesis scenarios require the symmetry under the combined action of charge conjugation (C) and parity (P) to be violated, at a level which is incompatible with the Standard Model (SM) of particle physics. The detection of an electric dipole moment (EDM) of a non-degenerate system would directly signal CP violation beyond the SM and constitute a background free signal of new physics. The current limit on the electron EDM (eEDM) is set by atomic and molecular optics experiments exploiting the extremely high internal electric field and unpaired electrons inside polar paramagnetic molecules. Remarkably, such low energy experiments, thanks to high precision spectroscopy methods, probe mass ranges of proposed CP-violating particles well beyond the direct reach of particle colliders. Molecules at ultracold temperatures are expected to provide more advanced quantum control, leading to several orders of magnitude gain in the eEDM sensitivity. However, the strategy to get there is yet unclear. In COMPASS, I will respond to this need and realize the first ultracold gas of eEDM-sensitive molecules, assembled from pre-cooled transition-metal chromium and closed-shell ytterbium atoms. This specific combination, overlooked thus far, provides an exceptional and timely opportunity to produce large samples of long-lived molecules with large internal electric field (15GV/cm) and high-polarizability to gain an order of magnitude in eEDM sensitivity via standard spin-precession measurements. Moreover, YbCr are amenable to engineering of clock transitions, and entanglement-enhanced quantum metrology, decoupling them from external electromagnetic field noise. Finally, COMPASS will pave the way to the realization of a whole new class of isovalent species for semi-leptonic, and even hadronic CP violation searches.