Electroassociation of ultracold dipolar molecules into long-range tetramer states

The presence of electric or electromagnetic fields can modify the long-range forces between ultracold dipolar molecules in such a way as to engineer weakly bound states of molecule pairs. These so-called "field-linked states" have been predicted about twenty years ago in a static electric field [1] and more recently in a microwave field [2]. Such long-range states, in which the separation between the two bound molecules can be orders of magnitude larger than the molecules themselves, have been observed as resonances in scattering experiments [3].

Here, I will present how to associate two ultracold dipolar molecules into such a bound long-range tetramer state by ramping the value of the electric field of the microwave that engineers those states. This electroassocation process [4, 5], recently observed in an experiment [5], shares a lot in common with magnetoassociation for which one can associate two ultracold atoms into a long-range diatomic molecule using a ramp of a magnetic field [6]. This method can be a primary step to form ultracold ground-state tetramers [7].

[1] A. V. Avdeenkov and J. L. Bohn, "Linking Ultracold Polar Molecules", Phys. Rev. Lett. 90, 043006 (2003)

[2] L. Lassablière and G. Quéméner, "Controlling the Scattering Length of Ultracold Dipolar Molecules", Phys. Rev. Lett. 121, 163402 (2018)

[3] X.-Y. Chen et al., "Field-linked resonances of polar molecules", Nature 614, 59 (2023)

[4] G. Quéméner, J. L. Bohn, James F. E. Croft, "Electroassociation of Ultracold Dipolar Molecules into Tetramer Field-Linked States", Phys. Rev. Lett. 131, 043402 (2023)

[5] X.-Y. Chen et al., "Ultracold field-linked tetratomic molecules", arXiv2306.00962 (2023)

[6] T. Köhler et al., "Production of cold molecules via magnetically tunable Feshbach resonances", Rev. Mod. Phys. 78, 1311 (2006) ; C. Chin et al., "Feshbach resonances in ultracold gases", Rev. Mod. Phys. 82, 1225 (2010)

[7] N. V. Vitanov et al., "Stimulated Raman adiabatic passage in physics, chemistry, and beyond", Rev. Mod. Phys. 89, 015006 (2017) ; J. Pérez-Ríos, M. Lepers, and O. Dulieu, "Theory of long-range ultracold atom-molecule photoassociation", Phys. Rev. Lett. 115, 073201 (2015).