Physicists use a new ultracold limit to create a state of matter

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Like water molecules, these molecules are polar, meaning they carry both a positive and a negative charge.
The team came close to creating molecular BEC last fall in work published in Nature Physics that introduced the microwave shielding method.
A new world for quantum physics opens Ye, a pioneer of ultracold science based in Boulder, considers the results a beautiful piece of science.
“Will’s experiment features precise control of molecular interactions to steer the system toward a desired outcome—a marvelous achievement in quantum control technology.”
Most ultracold experiments take place within a second—some as short as a few milliseconds—but the lab’s molecular BECs last upwards of two seconds.
“That will really let us investigate open questions in quantum physics,” he said.
This would enable powerful quantum simulations that mimic the interactions in natural crystals, noted Will, which is a focus area of condensed matter physics.
“The molecular BEC will introduce more flavor,” said Will.

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There is a brand-new, trendy BEC in town that has nothing to do with cheese, bacon, or eggs. It can be found in the coldest place in New York, not your neighborhood bodega, but in the laboratory of Columbia physicist Sebastian Will. Will’s experimental group focuses on raising atom and molecular temperatures to mere degrees above absolute zero.

Writing in Nature, the Will lab has successfully produced a unique quantum state of matter known as a Bose-Einstein Condensate (BEC) out of molecules with the help of theoretical collaborator Tijs Karman at Radboud University in the Netherlands.

Made of sodium-cesium molecules, their BEC is stable for an astonishingly long two seconds, even when cooled to just five nanoKelvin, or roughly -459 point 66°F. These molecules are polar, meaning they have two charges—a positive and a negative one—just like water molecules. Will pointed out that the long-range interactions that lead to the most fascinating physics are made possible by the uneven distribution of electric charge.

With their molecular BECs, the Will lab is eager to investigate a variety of quantum phenomena, such as novel forms of superfluidity—a state of matter that flows without encountering any friction. Additionally, they intend to use their BECs to create simulators that can replicate the mysterious quantum characteristics of more complicated materials, such as solid crystals.

The speaker stated, “Molecular Bose-Einstein condensates open up whole new areas of research, from understanding truly fundamental physics to advancing powerful quantum simulations.”. “While this is an exciting accomplishment, it’s only the beginning. “.”.

It’s been decades in the making for the broader ultracold research community, and a dream come true for the Will lab.

Add microwaves to make it colder.

At Columbia, microwaves have long been used as a type of electromagnetic radiation. Airborne radar systems were developed as a result of the groundbreaking work on microwaves done in the 1930s by physicist Isidor Isaac Rabi, who would go on to win the Nobel Prize in Physics.

“Rabi was a trailblazer in microwave research and one of the first to control the quantum states of molecules,” Will said. “We continue that ninety-year tradition with our work. “.

Microwaves are known for helping you heat food, but did you know that they can also help with cooling? Due to the propensity of individual molecules to collide, larger complexes that are formed will eventually evaporate from the samples. According to Karman, their Dutch collaborator, microwaves have the ability to form tiny shields around individual molecules, preventing them from colliding.

Author Niccolò Bigagli explained that because the molecules are protected from lossy collisions, only the hottest ones can be preferentially removed from the sample. This is the same principle of physics that cools your coffee when you blow on the top of it. The sample’s overall temperature will decrease as a result of the remaining molecules becoming colder.

Last fall, the group published work that introduced the microwave shielding method in Nature Physics, bringing them one step closer to creating molecular BEC. However, there was still another experimental twist that was required. The Will lab had been working toward crossing the BEC threshold since it opened at Columbia in 2018, and they were able to do so when they added a second microwave field, which improved cooling even further.

Following his Ph.D. graduation, Bigagli remarked, “This was fantastic closure for me.”. B. , having been a founding member of the lab in physics this spring. “These amazing results are what we got from not having a lab setup yet. “.

The second microwave field can not only lessen collisions but also change the orientation of the molecules. Which brings us to the way the lab is currently investigating: controlling how they interact. “We aim to create new quantum states and phases of matter by controlling these dipolar interactions,” co-author and postdoc Ian Stevenson of Columbia said.

Quantum physics enters a new realm.

Ye, a Boulder-based pioneer in ultracold science, views the findings as a stunning work of science. “The research will significantly influence several scientific domains, such as quantum chemistry and the investigation of highly correlated quantum materials,” he stated. Will’s experiment demonstrates amazing advancements in quantum control technology by precisely controlling molecular interactions to direct the system toward a desired result. “.

In the meantime, the Columbia team is thrilled to have an experimentally verified theoretical explanation of molecular interactions. As for the next steps, such as investigating dipolar many-body physics, “we really have a good idea of the interactions in this system,” Karman stated. We developed interaction control schemes, put them to the test theoretically, and then carried them out in the experiment. Seeing these concepts for microwave “shielding” come to life in the lab has been truly amazing. “.”.

With the molecular BECs, dozens of theoretical predictions can now be tested experimentally, as co-first author and Ph. D. as noted by student Siwei Zhang, are fairly stable. Molecular BECs in the lab last up to two seconds, but most ultracold experiments happen in a matter of seconds, sometimes even milliseconds. That will allow us to really look into unanswered questions in quantum physics, he said.

Using BECs trapped in a laser-generated optical lattice, one concept is to produce artificial crystals. Will pointed out that this would enable powerful quantum simulations that emulate the interactions in natural crystals, a focus area of condensed matter physics.

Atoms are commonly used in quantum simulators, but their short-range interactions (they must essentially be on top of each other) restrict how well they can simulate more complex materials. Will said, “There will be more flavor introduced by the molecular BEC.”.

That encompasses dimensionality, according to Ph. and co-first author. B. student Yuan Weijun. “In a 2D system, we would like to use the BECs. There will always be new physics to emerge when you go from three dimensions to two,” he stated. Superconductivity and superfluidity are two examples of quantum phenomena that Will and his condensed matter colleagues may be able to investigate with the aid of a model system composed of molecular BECs. 2D materials constitute a significant scientific focus at Columbia.

“A seemingly endless array of opportunities appears to be emerging,” Will remarked.

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