Applications of shielded ultracold molecules: Formation of ultracold complexes and quantum magnetism

Ultracold polar molecules can be shielded against loss inside an optical trap using an external static electric or a microwave field. Shielded ultracold molecules have opened the doors to exploring new physics. For example, enhanced stability in the traps has enabled the realization of Bose-Einstein condensates and Fermi-degenerate samples of polar molecules. The external field, which enables shielding, also enables tuning the interaction by allowing us to control the sign and magnitude of the s-wave scattering length a. Furthermore, a can be tuned such that near-threshold bound states appear. These weakly bound states are called field-linked (FL) tetramer states. In our recent work, we have proposed a Stimulated Raman Adiabatic Passage (STIRAP) mechanism to transfer weakly bound FL tetramers to deeper bound states [1]. We consider static-electric-field shielded alkali diatomic molecules initially in their ground electronic state. We identify an excited electronic state for achieving the STIRAP transfer and propose proof-of-principle experiments.
In another recent work, we showed that shielded ultracold molecules allow quantum magnetism with SU(N) symmetry, where N can be as high as 32 [2]. This is unlike the case with atoms, with which SU(N) magnetism has been realized with N up to 10. In addition, SU(N) magnetism with shielded molecules can have both attractive and repulsive interactions. In conclusion, I would show in my talk how ultracold molecules provide exciting new opportunities, from creating polyatomic molecules to quantum magnetism.
[1] B. Mukherjee and M. Tomza, arXiv:2506.17341 (2025).
[2] B. Mukherjee, J. M. Hutson and K. R. A. Hazzard, New J. Phys. 27, 013013 (2025).