Ultracold atoms have been successfully used in quantum simulations and precision measurements. Molecules possess a richer internal structure promising new applications. However, only relatively simple molecules have been produced and employed at ultralow temperatures. This project aims to understand and harness the increasing complexity of ultracold polyatomic molecules to probe the fundamentals of chemistry and physics. We will extend the range of ultracold polyatomic molecules and their applications in controlled chemistry and precision spectroscopy. We will propose and theoretically investigate two paths: 1) association of ultracold deeply-bound diatomic molecules into ultracold weakly-bound polyatomic molecules and 2) direct cooling deeply-bound polyatomic molecules carefully selected and manipulated with electromagnetic fields. The first approach will build on established atomic techniques, which we will extend to molecular systems. The second one will employ strong fields, short pulses, and structural modifications to engineer closed transitions suitable for laser cooling. We will combine and develop novel electronic structure and quantum scattering methods enhanced by machine learning and high-performance computing. Next, we will study new applications exploiting features emerging from single-molecule and coherent control, conical intersections, and non-trivial electronic states and geometries absent in simpler systems. Applications will range from quantum-controlled chemical reactions and molecular dynamics to precision measurements of fundamental constants and their spatio-temporal variation. The realization of the project will push cold chemistry into the quantum realm and bring unprecedented complexity to ultracold physics, thus, give new insights into the physical basis of chemistry and the fundamental laws of nature. A unique experience of the PI in both quantum chemistry and ultracold atomic physics will be instrumental in achieving these goals.

There is currently growing interest in forming ultracold polyatomic molecules. It is anticipated that their rich internal structure will provide powerful platforms for quantum information processing, precision measurements, studies in cold-controlled chemistry, and simulation of quantum many-body systems. In a recent ground-breaking experiment, weakly bound ultracold tetratomic molecules (“tetramers”) have been realized from pairs of ultracold alkali-metal diatoms using external fields [Nature, 626, 283 (2024)]. It also opened a new question on how such weakly bound tetramers can be transferred to their absolute ground state. The main challenge is to mitigate their collisional loss from experimental traps which is expected to be very high due to an immense number of internal degrees of freedom. In this Action, I will propose novel theoretical methods to transfer weakly bound ultracold tetramers to deeply bound states in their ground electronic potential using lasers. To achieve this goal, I will combine two well-established methods for ultracold diatomic molecules: (a) Collisional shielding of molecules against inelastic and reactive loss, and (b) Stimulated Raman Adiabatic Passage (STIRAP) method for transferring weakly bound ultracold molecules to their ground vibronic state. I will implement the method (a) for molecules colliding in an excited electronic state required for STIRAP. I will develop a new method (b) which will enable the creation of deeply bound ultracold tetramers. Successful implementation of this project will create a new indirect method of creating ultracold polyatomic molecules in deeply bound states. The proposed method is near-universal and can be applied to a wide range of molecules. Stable gases of such molecules will allow the creation of a new type of Bose-Einstein Condensate made of polyatomic molecules. This Action will enable me to expand my skillsets in cutting-edge ultracold research and will help to launch my independent career.