Ultracold LiCr: A New Pathway to Quantum Gases of Paramagnetic Polar Molecules

Quantum gases of doubly polar molecules represent appealing frameworks for a variety of cross-disciplinary applications, encompassing quantum simulation and computation, controlled quantum chemistry, and precision measurements. Through a joint experimental and theoretical study, here we explore a novel class of ultracold paramagnetic polar molecules combining lithium alkali and chromium transition metal elements. Focusing on the specific bosonic isotopologue 6Li53Cr, leveraging on the Fermi statistics of the parent atomic mixture and on suitable Feshbach resonances recently discovered, we produce up to 50×103 ultracold LiCr molecules at peak phase-space densities exceeding 0.1, prepared within the least bound rotationless level of the LiCr electronic sextet ground state X6ς+. By also developing new probing methods, we thoroughly characterize the molecular gas, demonstrating the paramagnetic nature of LiCr dimers and the precise control of their quantum state. We investigate their stability against inelastic processes and identify a parameter region where pure LiCr samples exhibit lifetimes exceeding 0.2 s. Parallel to this, we employ state-of-the-art quantum chemical calculations to accurately predict the properties of LiCr ground and excited electronic states. This ab initio model, able to reproduce the experimental Li-Cr high-spin, octet scattering length, allows us to identify both efficient paths to coherently transfer weakly bound LiCr dimers to their absolute ground state, and suitable transitions for their subsequent optical manipulation. Our studies establish Li-Cr as a prime candidate to realize ultracold gases of doubly polar molecules with significant electric (3.3 D) and magnetic (5μB) dipole moments.