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NSF Hot for Carroll’s Research on Cold Atoms

For the third time, the National Science Foundation has funded Professor of Physics Tom Carroll’s research on ultracold Rydberg atoms, a collaboration with Professor of Physics Mike Noel of Bryn Mawr College.

The grant and the work are divided between the two campuses. Of the $540,530 total, $194,550 is for computational research at Ursinus and the remainder is for experimental work in the lab at Bryn Mawr.

The duo and their students use highly excited atoms called Rydberg atoms that have been cooled to a few hundred millionths of a degree above absolute zero. But—plot twist—they don’t study the atoms themselves.

“Rather, we take advantage of their unique properties to explore fundamental quantum mechanics,” says Carroll. “A pair of Rydberg atoms can interact with each other by exchanging energy; one atom loses the energy and the other atoms gains it. These interactions are ‘resonant,’ meaning that they can only take place when external conditions allow energy to be conserved. The external conditions include electric fields, magnetic fields, and lasers, and are under our control.” Therefore, they can exert some control over the behavior of the atoms.

“All of this takes place in a magneto-optical trap (MOT), which is housed in a vacuum chamber at pressure that is about a trillion times lower than atmospheric pressure,” says Carroll. “The apparatus is about the size of a basketball and you can fit the entire experiment on a big dining room table.”

Ursinus students participate in all aspects of the work and typically travel with Carroll to Bryn Mawr, where the MOT is located, at least two days per week in the summer. This year the work went online due to COVID-19, and Carroll met daily with Alicia Handian ’21, as well as Nina Inman, a 2020 graduate from Bryn Mawr, who performed simulations remotely. “We also communicated regularly by texting, though difficult quantum questions produce some pretty long and confusing texts,” says Carroll.

In this new grant, which is funded through August 2023, the aim is to explore two main avenues: thermodynamic behavior of the atoms and “many-body” interactions (recent discoveries have simultaneously involved triplets and quadruplets of Rydberg atoms).

“There is great interest in understanding the fundamental physics of groups of quantum mechanically interacting atoms,” says Carroll. “This is particularly true for understanding the physics of solids … Solids are hard to study at this level because they interact strongly and, well, they’re mostly opaque. In the past 10 years, systems of cold atoms have helped to solve this problem. We can engineer groups of cold Rydberg atoms that interact strongly like in a solid, but are far enough apart that we can study them in greater detail. Our plan is to explore how groups of these atoms thermalize, especially in cases where many-body interactions play a role.”