Physicists at Columbia University, led by Sebastian Will, have created a unique state of matter known as a Bose-Einstein Condensate (BEC) from sodium-cesium molecules. The molecules were cooled to just five nanoKelvin, or about -459.66 °F, and remained stable for two seconds. The team used microwaves to cool the molecules, a method proposed by collaborator Tijs Karman at Radboud University in the Netherlands. The creation of this molecular BEC opens up new areas of research in quantum physics, including the exploration of superfluidity and the simulation of complex materials like solid crystals.
A Quantum Leap in Ultracold Physics
In a groundbreaking experiment, physicists at Columbia University have successfully created a Bose-Einstein Condensate (BEC) from sodium-cesium molecules. This unique quantum state of matter, cooled to an astonishing five nanoKelvin, or about -459.66 °F, and stable for an impressive two seconds, is a significant achievement in the field of ultracold physics. The creation of this molecular BEC opens up new avenues for research, from exploring different quantum phenomena to simulating the quantum properties of more complex materials.
The science of BECs dates back to the early 20th century when physicists Satyendra Nath Bose and Albert Einstein predicted that a group of particles cooled to near standstill would coalesce into a single, larger superentity governed by the laws of quantum mechanics. The first atomic BECs were created in 1995, a feat that was recognized with the Nobel Prize in Physics in 2001. However, creating a BEC from molecules, which are more complex than atoms, has proven to be a more challenging task.
The Journey to Molecular BECs
The journey to creating molecular BECs has been a long one. The first breakthrough came in 2008 when physicists at JILA in Boulder, Colorado, cooled a gas of potassium-rubidium molecules down to about 350 nanoKelvin. However, to cross the BEC threshold, even lower temperatures were needed. In 2023, the Columbia team created the first ultracold gas of sodium-cesium molecules using a combination of laser cooling and magnetic manipulations. To achieve even lower temperatures, they turned to microwaves.
The Role of Microwaves in Cooling
Microwaves, a form of electromagnetic radiation, have a long history at Columbia. In the 1930s, physicist Isidor Isaac Rabi did pioneering work on microwaves that led to the development of airborne radar systems. While microwaves are commonly associated with heating food, they can also facilitate cooling. Microwaves can create small shields around each molecule that prevent them from colliding, an idea proposed by Tijs Karman, a collaborator at Radboud University in the Netherlands. With the molecules shielded against lossy collisions, only the hottest ones can be preferentially removed from the sample, thereby reducing the overall temperature.
Crossing the BEC Threshold
The Columbia team came close to creating a molecular BEC in 2023 using the microwave shielding method. However, it was the addition of a second microwave field that made cooling even more efficient and allowed sodium-cesium to finally cross the BEC threshold. This achievement was a significant milestone for the Columbia team, which had been working towards this goal since its establishment in 2018. The second microwave field not only reduced collisions but also manipulated the molecules’ orientation, providing a means to control how they interact.
Opening New Frontiers in Quantum Physics
The creation of a molecular BEC opens up a new world of possibilities in quantum physics. The Columbia team is excited to have a theoretical description of interactions between molecules that have been validated experimentally. There are dozens of theoretical predictions that can now be tested experimentally with the molecular BECs. One idea is to create artificial crystals with the BECs trapped in an optical lattice made from lasers. This would enable powerful quantum simulations that mimic the interactions in natural crystals. The molecular BEC could also help explore quantum phenomena including superconductivity, superfluidity, and more.
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