Author: Caroline Cichocki

Dear Friends of UConn Physics

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As we approach the beginning of the 2021-22 school year, UConn is set for having classes in person again, students on campus, and our first taste of somewhat normal university life in a year and a half. Students, faculty, and staff are all required to be vaccinated, masks are required indoors, classrooms will be fully utilized and our labs are fully open once again. As with the rest of America, we are both excited to be coming back but nervous about what the future may hold.

The past year has been difficult for us, as with everyone else. We had been teaching most classes remotely, research labs have been open but running at reduced capacity, and our new physics building has been eerily quiet for the most part. What has surprised me the most has been the number of successes racked up within the department despite the trying times. Within this newsletter there are some great stories on some accomplishments, including the UConn contribution to the world-famous muon g-2 result, our part in the new world of multi-messenger astronomy, and Nora Berrah’s prestigious term as a Blaise Pascal International Scholar. This has also been one of our best years in winning external research funding, with particularly notable successes among our newer hires.

Another development over the past year is that the renovations of the new physics building have been largely completed and it is fully open, including the new Light Court in the center of our studio teaching labs. Physics now occupies the space that was formerly the Mathematics Building. Unfortunately, I cannot yet extend an open invitation to come visit, but I hope you will do so once the pandemic recedes and we are fully open. Given uncertainty in the health situation, we still cannot schedule major public events for this year. Our next Katzenstein Lecture is scheduled for September 23, 2022. The speaker will be Donna Strickland from the University of Waterloo (Canada), the 2018 Nobel Laureate for developing chirped pulse amplification – a key ingredient in today’s ultrafast laser technology. When the time comes, we will be sending out invitations. I hope many of you can attend the lecture, visit our building, and attend the following banquet.

I close by wishing all of us health and a successful return to a more normal kind of life over the next year.

 

Barry Wells

Physics Department Head

Physics alumnus Prof. Douglas Goodman and Professor Emeritus Winthrop Smith Featured in Online Peer Review Journal

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Prof. Emeritus Winthrop Smith and former student Prof. Douglas Goodman (Quinnipiac University) Edit Special Issue of Open Access Journal Atoms, on Low Energy Interactions between Ions and Ultracold Atoms

 The Special Issue of the online journal Atoms is a collection of current peer-reviewed articles by experts in the field of ultracold collisions and reactions involving ions and atoms co-trapped by electromagnetic fields in a common volume (a hybrid ion-neutral trap). Prof. Goodman, a recent UConn Ph.D. student of Prof. Smith (2015) who worked with hybrid traps for his dissertation, is now on the faculty of Quinnipiac University in Hamden, CT.

Prof. Smith’s research, on which he supervised four doctoral dissertations over the last few years, centers around the study of low-energy ion-neutral collisions. At long range, universal types of charge-induced polarization effects produce very large elastic, inelastic, reactive, and charge-transfer cross-sections leading to a high interaction probability between ions and neutral atoms at low temperature. The Special Issue articles highlight recent experimental and simulation work in this field and discuss the outlook for future developments.

Two of the manuscripts in this Special Issue explore recent advances in hybrid trap technology. The paper by Prof. Karpa explains the use of bichromatic optical dipole traps, which can be used instead of the previously developed hybrid rf ion trap and magneto-optic trap. This remarkable new technique avoids the use of rf fields and associated micromotion heating limitations and allows access to the long-sought quantum-dominated regime of interaction.

Karpa, L. Interactions of Ions and Ultracold Neutral Atom Ensembles inComposite Optical Dipole Traps: Developments and Perspectives. Atoms2021, 9(3), 39; https://doi.org/10.3390/atoms9030039 The manuscript included by Prof. Denschlag’s team, early practitioners of hybrid-trap ion-neutral studies, introduces a novel type of low-energy reaction. Denschlag’s group discusses the interaction between an atomic ion and an atom with a valence electron in a highly excited Rydberg state that reacts to yield a long-range atom-ion Rydberg molecule, with binding lengths up to the micrometer scale.Deiß, M.; Haze, S.; Hecker Denschlag, J. Long-Range Atom–Ion RydbergMolecule: A Novel Molecular Binding Mechanism. Atoms 2021, 9(2), 34;https://doi.org/10.3390/atoms9020034 https://www.mdpi.com/2218-2004/9/2/34

The remaining two manuscripts in this Special Issue address important phenomenology of rf Paul traps as they are used in ion-neutral interaction experiments. The paper by Prof. Blumel analyzes the properties of ion clouds loaded from a magneto-optical trap in a hybrid ion-neutral system. He develops theoretical predictions for optimal loading conditions for hybrid-trap experiments, which are supported by numerical simulations. Additionally, he predicts the existence of a new type of ion heating mechanism caused by the increase in Coulomb energy associated with each newly loaded ion within the existing ion-cloud volume.

Blümel, R. Loading a Paul Trap: Densities, Capacities, and Scaling inthe Saturation Regime. Atoms 2021, 9(1), 11; https://doi.org/10.3390/atoms9010011https://www.mdpi.com/2218-2004/9/1/11

Last, the manuscript by Prof. Rangwala’s group, numerically and analytically explores the benefits of using linear multipole rf traps for studying low-energy ion-neutral collisions, as opposed to the conventional quadrupole ion-trap configuration. Using new analyses of the heating effects, Rangwala’s group shows that the higher-order multipolar trap configurations reduce unwanted heating in the ion-neutral system. In doing so, they develop a methodology for comparing and optimizing hybrid trap designs.

Niranjan, M.; Prakash, A.; Rangwala, S. Analysis of Multipolar Linear

Paul Traps for Ion–Atom Ultracold Collision Experiments. Atoms 2021,

9(3), 38; https://www.mdpi.com/2218-2004/9/3/38

https://doi.org/10.3390/atoms9030038

New Faculty Hire-Dr. Anh-Thu Le

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The Physics Department welcomes our newest faculty member, Dr. Anh-Thu Le, although he prefers to be called simply AT. AT worked for many years at the well-known James R. Macdonald Laboratory, rising to the rank of Research Professor. He worked alongside a world-known theorist, Dr. Chii-Dong Lin. Dr. Le went on to become an Assistant Professor at Missouri University of Science and Technology before coming to UConn. Dr. Le is well-versed in current theoretical methods for exploring the interaction of ultrafast lasers with atoms and molecules. He has a strong overlap with the ultrafast AMO experimental programs at UConn and has collaborated with high-profile experimental groups.

Dr. Le has a thoroughly international and diverse background, having grown up in the Vietnamese countryside. His research career has taken him from Vietnam to the Republic of Belarus, Germany, Canada, and ultimately the US. This has left him with a lasting commitment to serving diverse populations, both in the classroom and in his research.

Stretching Makes Superconductor

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October 12, 2020 – Kim Krieger – UConn Communications

When people imagine new materials, they typically think of chemistry. But UConn physicist Ilya Sochnikov has another suggestion: mechanics.

Sochnikov works with superconductors. Superconductors are materials that let electricity flow without losing energy. In a normal conductor — say, a power line — electric current is gradually whittled down by friction and loss. We lose as much as 90% of the electricity we generate this way. But an electric current could flow through a superconducting circuit forever, unchanging. Practical superconductors would make power grids and many devices, including new computers, much more energy efficient.

Chemists and metallurgists have experimented with different combinations of elements for years, trying to get superconductors that work at temperatures close to room temperature (most superconductors only work when they are super cold.) The idea is to come up with the perfect combination of elements that will have exactly the right density of electrons, at the right energies. When that happens, electrons pair up and move through the material in a synchronized way, even at temperatures above 77 degrees Kelvin, which is the temperature of liquid nitrogen. That is considered a high-temperature superconductor, because liquid nitrogen is cheap to produce and can be used as a refrigerant. But finding the right chemistry to make new and better high-temperature superconductors has been elusive.

Sochnikov and his students are thinking about it differently. What if mechanical changes such as squeezing or stretching could make a material a superconductor? Changing the chemistry is ultimately about changing the arrangement of atoms and electrons in a material. Mechanical stresses can do the same thing, in a different way.

Along with Physics Department students Chloe Herrera, Jonah Cerbin, Donny Davino, and Jacob Franklin, Sochnikov designed a machine to stretch a small piece of superconductor to see what would happen. They picked strontium titanate, a well-known material used in high-tech electronics applications as big and almost perfect crystals, which becomes a superconductor around 0.5 degrees Kelvin. That is ridiculously cold, colder even than liquid helium. But strontium titanate behaves in a very weird way when it is that cold. Its atoms polarize; that means they all oscillate in synchrony. You can imagine them bouncing gently up and down, all together. These oscillations have a tendency to link electrons together, helping them move as a pair–this is probably what makes it superconduct.

Sochnikov and the students in the group knew that stretching strontium titanate would change how its atoms oscillated. That, in turn, might change how the electrons moved. The machine that stretches the crystal is made from copper to conduct heat away from the crystal. Most of the rest of the workings are coated in gold to reflect heat from the outside. It uses three cylinders to cool the material; first to the temperature of liquid nitrogen (70K), then liquid helium (4K), then to a boiling mixture of helium-3 and helium-4 (due to weird quantum effects, it is even colder than regular liquid helium–just a few thousandths of Kelvin! Really close to absolute zero!)

The whole setup is suspended in a steel frame that floats on shock absorbers, to prevent any vibrations in the floor from disturbing the experiment.

When Sochnikov, Herrera, Cerbin, Davino, and Franklin did the experiment and looked at the results, they found that stretched strontium titanate becomes superconducting at temperatures 40% higher than normal. That is a huge increase, percentage-wise. They believe it is because stretching the material makes it easier for the atoms to oscillate, gluing the electrons together more firmly. Now, they are working to calculate what made the difference, and plan on testing it in other materials in the near future.

“Usually we control materials chemically. Here, we do it mechanically. This gives us another tool to bring superconductors closer to everyday life, and to discover new functionalities,” Sochnikov says.

This article first appeared online on UConn Today, October 12, 2020.