Scientists have produced a rare form of quantum matter known as a Bose-Einstein condensate (BEC) using molecules instead of atoms.
Made from cold sodium-cesium molecules, these BECs are as cold as five nanoKelvin, or about -459.66 °F, and remain stable for a remarkable two seconds.
“These molecular BECs open up a new research arena, from understanding really fundamental physics to advancing powerful quantum simulations,” noted Columbia University physicist Sebastian Will. “We’ve reached an exciting milestone, but it’s only the beginning.”
Understanding Bose-Einstein Condensate (BEC)
A Bose-Einstein condensate (BEC) represents a state of matter that occurs when a collection of bosons, particles that follow Bose-Einstein statistics, are cooled to temperatures very close to absolute zero.
Under such extreme conditions, a significant fraction of bosons occupy the lowest quantum state, resulting in macroscopic quantum phenomena.
This means that they behave as a single quantum entity, effectively “collapsing” into a single wave function that can be easily described using the principles of quantum mechanics.
The fascinating aspect of BECs stems from their superfluid properties – exhibiting zero viscosity as they flow, which allows them to move without dissipating energy.
This unique property enables BECs to simulate other quantum systems and explore new realms of physics.
For example, the study of BECs can provide insights into quantum coherence, phase transitions, and many-body interactions in quantum gases.
The creation of molecular BECs, such as those involving sodium-cesium molecules, extends this exploration even further, potentially leading to breakthroughs in quantum computing and precision measurements.
BEC ultra cool odyssey
The journey of BECs is long and winding, dating back a century to the works of physicists Satyendra Nath Bose and Albert Einstein.
They prophesied that a group of particles cooled to the brink of stopping would coalesce into a single macro-entity, governed by the dictates of quantum mechanics. The first true atomic BECs appeared in 1995, 70 years after the original theoretical predictions.
Atomic BECs have always been relatively simple—round objects with minimal polarity-based interactions. But the scientific community began looking for a more complex version of BECs assembled from molecules, albeit to no avail.
Finally, in 2008, the first breakthrough came when a pair of physicists cooled a gas of potassium-rubidium molecules to about 350 nanoKelvin. The quest to achieve an even lower temperature to pass the BEC threshold continued.
Microwaves: The cooling solution
In 2023, the initial step toward this goal was achieved when the research group created their desired ultracold sodium-cesium molecular gas using a mixture of laser cooling and magnetic manipulation. To lower the temperature further, they decided to introduce microwaves.
Microwaves can build small shields around each molecule, preventing them from colliding and leading to a drop in the overall temperature of the sample.
Moving into the era of quantum control
The group’s achievement of creating a molecular BEC represents a spectacular achievement in quantum control technology.
This outstanding piece of scientific work will impact a host of scientific fields, from the study of quantum chemistry to the exploration of complex quantum materials.
“We really have a complete understanding of the interactions in this system, which is vital for later steps like exploring many-body dipolar physics,” said co-author and Columbia postdoc Ian Stevenson.
The research team developed schemes to control the interactions, tested them from a theoretical angle and executed them in the actual experiment. It’s truly amazing to witness these microwave ‘shielding’ concepts come to fruition in the lab.
Unfolding a new canvas in quantum physics
The creation of molecular BECs enables the fulfillment of many theoretical predictions. The stable nature of these molecular BECs allows for extensive exploration of quantum physics.
A proposal to construct artificial crystals with BECs held in a laser-made optical lattice could provide a comprehensive simulation of the interactions in natural crystals.
With the transition from a three-dimensional system to a two-dimensional one, new physics is expected to emerge. This field of research opens up a wealth of possibilities in the study of quantum phenomena, including superconductivity and superfluidity, among others.
“This feels like a whole new universe of possibilities being discovered,” concluded Sebastian Will, summing up the excitement in the scientific community.
BEC: From atoms to molecules
In summary, this research demonstrates the successful creation of a Bose-Einstein condensate (BEC) using ultracold sodium-cesium molecules, reaching a steady state at five nanoKelvin for two seconds.
Using a combination of laser cooling, magnetic manipulations and innovative microwave shielding, the research group and their theoretical collaborator achieved unprecedented control over molecular interactions at quantum levels.
This milestone enables the comprehensive exploration of quantum phenomena such as coherence, phase transitions and many-body interactions, potentially opening new avenues in quantum simulations, quantum computing and precision measurements.
The full study is published in the journal Nature.
Special thanks to Ellen Neff from Columbia University.
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