Breaking new ground in the field of quantum physics, a team of experimentalists at the Max Planck Institute of Quantum Optics (MPQ) and theorists at the Chinese Academy of Sciences (CAS) have achieved a remarkable feat. For the first time, they have successfully populated and stabilized a new type of molecule known as field-linked tetratomic molecules, or “supermolecules.” These extraordinary entities can only exist at ultracold temperatures and offer immense potential for advancing our understanding of exotic ultracold matter. This groundbreaking research, published in Nature, marks a significant milestone in molecular physics.
Decades ago, American theoretical physicist John Bohn and his colleagues predicted the possibility of a unique binding mechanism between polar molecules. When polar molecules possess asymmetrically distributed charges, they can combine in an electric field to form weakly bound supermolecules. Analogous to compass needles, these polar molecules experience an attraction stronger than the Earth’s magnetic field when brought close together. Instead of aligning north, they point towards each other, just like a dancing couple in a firm, yet constantly distanced embrace.
Supermolecules exhibit a distinct characteristic, possessing a bond length hundreds of times longer than traditionally bound molecules. This inherent long-range nature makes them highly sensitive to changes in the electric field, leading to a phenomenon known as “field-linked resonance.” With the flexibility to alter the shape and size of these molecules using a microwave field, researchers can explore new avenues in molecular manipulation.
While ultracold polyatomic molecules hold immense potential for various fields, including cold chemistry, precision measurements, and quantum information processing, their high complexity poses significant challenges in cooling. Conventional cooling techniques like direct laser cooling and evaporative cooling fall short when applied to polyatomic molecules. However, researchers at MPQ’s “NaK Lab” have made impressive strides in overcoming this hurdle.
In 2021, these researchers developed a novel cooling technique for polar molecules by utilizing a high-power rotating microwave field. Through this groundbreaking approach, they achieved a record-breaking low temperature of 21 billionths of a degree above absolute zero. Building upon this achievement, the team successfully observed the signature of binding between polar molecules in scattering experiments, providing indirect evidence of the existence of these long-predicted exotic constructs.
Direct Evidence of Supermolecules
Expanding upon their previous milestone, the researchers at MPQ have made a significant breakthrough by creating and stabilizing supermolecules in their experiments. Through advanced imaging techniques, these “supermolecules” reveal a unique p-wave symmetry, which holds crucial implications for the realization of topological quantum materials. These materials, in turn, could play a pivotal role in fault-tolerant quantum computation.
Xing-Yan Chen, Ph.D. Candidate and first author of the paper, emphasizes the far-reaching implications of this research. The method developed by the team is applicable to a wide range of molecular species, enabling the exploration of a vast variety of ultracold polyatomic molecules. This opens up possibilities for creating even larger and longer-living molecules, which could have profound applications in precision metrology and quantum chemistry.
The collaboration between MPQ and CAS has been instrumental in these findings. Prof. Tao Shi and his team at CAS have played a crucial role in advancing our understanding of supermolecules. Dr. Xin-Yu Luo, the principal investigator of the experiment, expresses their next goal: to further cool these bosonic supermolecules and form a Bose-Einstein condensate (BEC), where the molecules move together collectively. This holds immense potential in our fundamental comprehension of quantum physics.
The successful creation and stabilization of field-linked tetratomic molecules, or supermolecules, by the team at MPQ and CAS represent a crucial leap forward in the study of ultracold matter. These fragile entities, existing only at ultracold temperatures, offer unprecedented opportunities for exploring new frontiers in molecular physics. With their remarkable properties and potential applications in various fields, supermolecules pave the way for groundbreaking advancements in cold chemistry, precision measurements, and quantum information processing. As researchers continue to delve into the mysteries of ultracold matter, the future holds exciting prospects for our fundamental understanding of quantum physics.
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