An article published in the journal Nature discussed a recent breakthrough achieved by physicists in creating a Bose-Einstein condensate (BEC) using molecules for the first time.
Study: Molecules Form First-Ever Bose-Einstein Condensate. Image Credit: ImageFlow/Shutterstock
The Strange Behavior of Matter
In the 1920s, quantum physicists predicted that matter would start behaving strangely when cooled to close to absolute zero. Specifically, Heisenberg's uncertainty principle states that a particle's position is more uncertain when its momentum is more precisely known.
Thus, when a matter is cooled to the extent that it becomes almost stationary, its position uncertainty increases substantially. The particles overlap to occupy a lowest-energy single quantum state, a BEC, and become indistinguishable when the uncertainty is greater compared to the distance between the particles.
This system demonstrates well-controlled collective quantum behavior at a macroscopic scale, allowing researchers to utilize it to simulate phenomena like the Hawking radiation emission from a model black hole and exotic kinds of magnetism. Condensates have been utilized in atomic clocks and quantum sensors.
Several efforts have been made to create BECs from stable molecules as molecules interact in a more complicated manner compared to atoms, providing richer opportunities for quantum technologies and research. However, cooling molecules to the billionths of a degree above absolute zero for creating a condensate and controlling them is extremely difficult compared to atoms.
Specifically, molecules can vibrate and rotate in ways that are not possible for atoms. Polar molecules possessing negatively and positively charged ends can interact through electromagnetic forces over long ranges. A molecular condensate can allow physicists to understand and simulate a broader range of phenomena as the long-range interactions can define the property of the matter around us.
Although loosely bound structures/Feshbach molecules have been previously coaxed into condensates, turning clouds of stable molecules into a condensates in the final cooling stage is challenging due to chemical reactions between the colliding molecules. The interactions heat the molecules, which results in their escape from the cloud.
The Recent Development
In a recent study, physicists have successfully cooled molecules down to an extent that hundreds of molecules lock in step, forming a gigantic single quantum state. Since 1995, physicists have created similar states, referred to as BECs, using atoms, and utilized them to understand different quantum phenomena.
This study has devised a novel approach to prevent collisions in a polar molecule cloud, each made from one cesium and one sodium atom.
Researchers applied two types of microwave fields to the polar molecule cloud to make the molecules oscillate and rotate. Collectively, these microwave fields oriented the polar molecules in a manner to ensure that they always repel each other, which is the most crucial requirement to turn the molecule clouds into condensate.
Most importantly, this repulsion prevented the collision of molecules and allowed the researchers to further cool the molecules without losing too many of them by removing the hottest ones. This resulted in a condensate of over 1,000 molecules that was cooled to 6 billionths of a degree above absolute zero, a BEC's hallmark.
Significance of this Development
Molecular BECs can form the foundation of new kinds of quantum computers or provide solutions to fundamental questions. They can be used for creating exotic supersolid phases, where a rigid material can flow without resistance.
Although this has been realized in atomic gases with magnetic interactions until now, it can now be achieved in polar molecules. Physicists can test predictions about the behavior of this strange matter. Additionally, the system can separate into quantum droplets, a new matter phase, by adjusting the microwave fields to allow minor interactions between molecules.
Researchers anticipate the opportunity to observe molecules forming a type of crystal as they arrange themselves under a microscope. This arrangement is facilitated by confining the condensate within two dimensions using lasers—a phenomenon not previously achieved in any study. The structured condensate molecules could potentially form the foundation for new quantum computing technologies.
Specifically, the molecules can be separated to form qubits, information units in a quantum computer, as every molecule remains in a known, identical state. Moreover, the quantum rotational states of the molecules, which can be utilized for storing information, remain robust for minutes at a time, allowing complex and long calculations.
To summarize, the successful coaxing of molecules into BECs will stimulate and inspire the cold-molecules community for further research in this field.
Journal Reference
Gibney, E. (2024). Physicists coax molecules into exotic quantum state — Ending decades-long quest. Nature. https://doi.org/10.1038/d41586-024-01662-9, https://www.nature.com/articles/d41586-024-01662-9
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Article Revisions
- Jun 12 2024 - Title changed from "Molecules Form First-Ever Bose-Einstein Condensate" to "Physicists Achieve First-Ever Molecular Bose-Einstein Condensate"