First supercooled triatomic molecular system with high phase space density prepared by CSU
Pan Jianwei and Zhao Bo of the University of Science and Technology of China (USTC) have prepared the first supercooled triatomic molecular system synthesis with high phase space density in the international arena using coherent synthesis method. In this study, they prepared ultracold triatomic molecular systems from a simplified sodium-potassium molecule-potassium atom mixture near the ground state diatomic molecule and atomic Feshbach resonance using magnetic conjoining technique, which is an important step toward the study of ultracold molecule-based ultracold quantum chemistry and quantum simulation. The research results were published in the international authoritative academic journal Science on Dec. 2, Beijing time.
The use of highly controllable ultracold molecules to simulate complex and difficult-to-compute chemical reaction processes allows for accurate all-around studies of complex systems, and thus has a wide range of applications in ultracold chemistry and new material design. However, the complexity of the internal vibrational energy levels of molecules and the lack of cyclic jumps required for laser cooling make it very difficult to prepare ultracold molecules by direct cooling methods. With the development of cold atom technology, the coherent synthesis of ultracold molecules from ultracold atoms provides a completely new way to prepare ultracold molecular systems.
In 1998, the Feshbach resonance in atoms was observed by Wolfgang Ketterle's group at MIT [Nature 392, 151 (1998)], and in 2003, Deborah Jin's group at the University of Colorado used the Feshbach resonance in atoms to develop magnetic conjugation techniques to prepare potassium diatomic molecules [Nature 424, 47 ( 2003)]. Diatomic molecules prepared from ultracold atoms have the advantages of high phase space density and low temperature, and can be coherently transferred to the vibrational ground state by laser. In recent years a variety of diatomic molecules from alkali metal atoms have been prepared in other laboratories and have been widely used in the study of ultracold chemistry and quantum simulations.
With the great success in the study of diatomic molecules, people began to study how to prepare ultracold triatomic molecules. However, since triatomic molecules are extremely complex and cannot be calculated theoretically, it has been an open question whether a triatomic molecular system can be prepared using coherent synthesis. The Feshbach resonance between sodium-potassium molecules and potassium atoms at ultra-low temperatures was observed by a research team at CSU in 2019 [Science 363, 261 (2019)], laying the foundation for the synthesis of triatomic molecules. On this basis, a joint research group of CSU and Institute of Chemistry, Chinese Academy of Sciences (CAS) has achieved the RF synthesis of ultracold triatomic molecules near the Feshbach resonance of sodium-potassium ground state molecules and potassium atoms in early 2022 [Nature 602, 229 (2022)]. However, due to the short lifetime and low synthesis efficiency of triatomic molecules, indirect evidence for the synthesis of triatomic molecules can only be obtained through the loss of diatomic molecules or atoms, and the direct detection of triatomic molecules and the preparation of ultracold triatomic molecular systems remains a great experimental challenge.
In this study, starting from a quantum-simplified mixture of sodium-potassium molecules and potassium atoms, the team has successfully prepared for the first time an ultracold triatomic molecular system with high phase space density by a slow scanning magnetic field near the Feshbach resonance of sodium-potassium molecules and potassium atoms, adiabatically transferring the scattered state of sodium-potassium molecules-potassium atoms to the bound state of triatomic molecules, thereby using magnetic conjugation to coherently prepare an ultracold triatomic molecular system with high phase space density. atomic molecular systems with high phase space density. The team obtained the dissociation spectrum of triatomic molecules by dissociating the triatomic molecules into free sodium-potassium molecules and atoms using the RF dissociation technique, thus enabling the direct detection of triatomic molecules. The experimental results show that the phase space density of the obtained triatomic molecular gas is improved by about 10 orders of magnitude compared with other methods. The preparation of supercooled triatomic molecular systems paves the way to simulate the three-body problem under quantum mechanics, and the obtained high phase space density makes it possible to prepare Bose-Einstein condensation of triatomic molecules. The reviewers agreed that this work is a milestone in the field of ultracold molecular research and opens up new directions for the study of ultracold chemistry and quantum simulations.
This research work was funded and supported by the Ministry of Science and Technology, the Natural Science Foundation of China, the Chinese Academy of Sciences, Anhui Province, and Shanghai Municipality.
www.science.org/doi/10.1126/science.ade6307
