Controlling interactions between ultracold polar molecules by double microwave shielding

Microwave shielding with two fields of different frequency and polarization enables simultaneously suppressing two and three-body loss, and has recently led to the first Bose-Einstein condensate of polar molecules [1]. In addition, the two-color two-polarization scheme enables control over the long-range dipolar interaction between molecules, as well as offering tunability of the scattering length. This enables switching dipole-dipole interactions off, making them dominant, or tuning to any intermediate case, while controlling the anisotropy and sign (dipolar versus “anti-dipolar”) of the dipolar interactions; in other words, we obtain complete control of dipolar interactions while suppressing two and three-body loss. Strong dipole-dipole interactions in a degenerate gas of molecules are predicted to lead to self-bound droplets and other new and exotic phases of matter [2].

[1] “Observation of Bose-Einstein Condensation of Dipolar Molecules”, Bigagli et al. arXiv:2312.10965

[2] “Self-bound dipolar droplets and supersolids in molecular Bose-Einstein condensates” Schmidt, Lassablière, Quéméner, and Langen Phys. Rev. Research 4, 013235 (2022)