In a groundbreaking achievement, a team of experimentalists at the Max Planck Institute of Quantum Optics (MPQ) and theorists at the Chinese Academy of Sciences (CAS) have successfully created and stabilized a new type of molecule known as field-linked tetratomic molecules. These “supermolecules” have only been able to exist at ultracold temperatures, and their existence has long been suspected but never demonstrated until now. This significant discovery in molecular physics opens up new avenues in the study of exotic ultracold matter. The details of this breakthrough are published in the prestigious journal Nature.
Nearly two decades ago, theoretical physicist John Bohn and his colleagues proposed the existence of a unique type of binding between polar molecules. They theorized that if these molecules carried an asymmetric charge distribution or polarity, they could combine in an electric field and form weakly bound supermolecules. This behavior can be likened to compass needles inside a hard shell. Instead of aligning north as expected, when these polar molecules are brought close together, they experience a stronger attraction towards each other, forming a distinct bound state due to electrical forces. The bond between these supermolecules is weaker than typical chemical bonds but extends over significantly longer distances. This long-range nature gives them high sensitivity, with even slight changes in the electric field parameters leading to dramatic alterations in the forces between the molecules, known as “field-linked resonance.”
Ultracold polyatomic molecules possess a complex internal structure that offers exciting possibilities in fields such as cold chemistry, precision measurements, and quantum information processing. However, their complexity presents a significant challenge when it comes to conventional cooling techniques like direct laser cooling and evaporative cooling, which are better suited for simpler diatomic molecules. Overcoming this challenge has been a focus of researchers at the “NaK Lab” (sodium potassium lab) at MPQ.
Led by Dr. Xin-Yu Luo, Dr. Timon Hilker, and Prof. Immanuel Bloch, the NaK Lab has achieved several pioneering discoveries that have paved the way for the creation of field-linked tetratomic supermolecules. In 2021, they invented a novel cooling technique using a high-power rotating microwave field, which allowed them to set a new low-temperature record of 21 billionths of a degree above absolute zero. A year later, they successfully observed the signature of binding between polar molecules in scattering experiments, providing indirect evidence for the existence of these theoretically predicted constructs. Now, through their latest experiment, the researchers have directly created and stabilized these supermolecules.
Imaging of these newly created supermolecules revealed their unique p-wave symmetry, which is crucial for the realization of topological quantum materials. These materials have the potential to be used in fault-tolerant quantum computation, making this discovery particularly significant in the field of quantum physics. Moreover, the method used to create these supermolecules can be applied to a wide range of molecular species, allowing for the exploration of a greater variety of ultracold polyatomic molecules. Looking ahead, this technique holds the possibility of creating even larger and longer-living molecules, which would be of great interest to precision metrology and quantum chemistry.
The researchers’ next goal is to further cool these bosonic supermolecules to form a Bose-Einstein condensate (BEC), where the molecules collectively move together. This achievement would have profound implications for our fundamental understanding of quantum physics. The collaboration between the Max Planck Institute of Quantum Optics and the Chinese Academy of Sciences has proven to be instrumental in advancing the field of molecular physics and exploring the frontiers of ultracold matter.
The creation and stabilization of field-linked tetratomic supermolecules at ultracold temperatures mark a significant milestone in molecular physics. This groundbreaking achievement opens up new possibilities in the study of exotic ultracold matter and has immediate and far-reaching implications in quantum physics. The ongoing research in this field will undoubtedly lead to further discoveries and a deeper understanding of the fascinating world of ultracold polyatomic molecules.
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