A New Pathway to Quantum Gases of Paramagnetic Polar Molecules

Quantum gases of paramagnetic polar molecules, namely compounds that combine a large electric dipole moment with a magnetic one, associated with a nonzero electronic spin, are regarded as pristine platforms for a wealth of quantum-technological applications and fundamental studies ranging from quantum simulation and computation to controlled quantum chemistry and precision measurements. Yet realization of quantum gases of doubly polar molecules, based on biatomic systems considered so far, remains an unsurpassed task. In our joint experimental and theoretical work, we solve this two-decade-old challenge by exploring a new class of paramagnetic polar molecules, obtained by binding lithium alkali and transition-metal chromium elements. Starting from an ultracold mixture of 6⁢Li and 53⁢Cr fermionic atoms, we efficiently produce a high phase-space-density, long-lived gas of bosonic 6⁢Li53⁢Cr dimers, prepared within a single, weakly bound vibrational level. Through state-of-the-art techniques and novel probing methods, we reveal the paramagnetic nature of this diatomic species, gain experimental control over its internal quantum state, and identify the main inelastic mechanisms that may limit the system stability. In parallel, we develop quantum-chemical calculations to build a complete model for the LiCr molecule. We predict a large electric dipole moment together with high electronic spin in the absolute ground state, and we identify suitable transitions both for the coherent transfer of our weakly bound LiCr dimers to their lowest rovibrational level and for their subsequent optical manipulation. Our studies establish an unparalleled new pathway to realize quantum gases of doubly polar molecules, with countless future applications in quantum science and technology.

S. Finelli et al.
Ultracold Li⁢Cr: A New Pathway to Quantum Gases of Paramagnetic Polar Molecules
PRX Quantum (2024)