News: Research

Reveals new form of spontaneous quantum scattering in a driven many-body system.

“This is a very fundamental behavior that we have never seen before; it was a great surprise to us,” said study author Cheng Chin, Professor of Physics and in the JFI. Published Nov. 6 in Nature, the research details a curious phenomenon — seen in what was thought to be a well-understood system — that may someday be useful in quantum technology applications.

Chin’s lab studies what happens to particles called bosons in a special state called a Bose-Einstein condensate. When cooled down to temperatures near absolute zero, bosons will all condense into the same quantum state. Researchers applied a magnetic field, jostling the atoms, and they began to collide—sending some flying out of the condensate. But rather than a uniform field of random ejections, they saw bright jets of atoms shooting together from the rim of the disk, like miniature fireworks.

The tiny jets may show up in other systems, researchers said and understanding them may help shed light on the underlying physics of other quantum systems.

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Utilizing gas-surface collisions on patterned silicon.

In a paper published in Physical Review Letters, a team led by Prof. Steven J. Sibener describes a way to separate isotopes of neon using a beam of gas aimed at a precisely patterned silicon wafer, which reflects the different isotopes at slightly different angles. The method could one day be a less costly and more energy-efficient way to separate isotopes for medicine, electronics and other applications.

“One can think about it like separating the various colors of light into a rainbow using a prism,” said Sibener, the Carl William Eisendrath Distinguished Service Professor of Chemistry and the James Franck Institute. “This is a wonderful and very precise demonstration study, and we are very pleased with the results,” Sibener said. “It has been a delight to run down to the lab every day to see what’s happened. We’re very much looking forward to planning the next steps in this project to explore other atoms and molecules.”

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For experiments and theory on the topological aspects of fluid dynamics and mechanical metamaterials.

William Irvine was recently elected a Fellow of the American Physical Society, nominated by the Topical Group on Soft Matter. The criterion for APS Fellow election is exceptional contributions to the physics enterprise; e.g., outstanding physics research, important applications of physics, leadership in or service to physics, or significant contributions to physics education. Fellowship is a distinct honor signifying recognition by one's professional peers.

Research for the Irvine group was recently featured on the cover of Physics Today. The Irvine Group at the University of Chicago has put a new twist on the smoke ring. Instead of blowing smoke into the air to create and visualize swirling flows known as vortex rings, they drove 3D-printed hydrofoils, lined with fluorescent dye, through water. Here, the wispy outer ring of white dye reveals a vortex ring; the orange and green trails are a tomographic reconstruction of the ring’s evolution over time. To learn how the group’s technique helped unveil hidden structure in fluid vortices, see the story.

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Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures.

In a study published Sept. 20 in Nature, UChicago and Cornell University researchers describe an innovative method to make stacks of semiconductors just a few atoms thick. The technique offers scientists and engineers a simple, cost-effective method to make thin, uniform layers of these materials, which could expand capabilities for devices from solar cells to cell phones.

“The scale of the problem we’re looking at is, imagine trying to lay down a flat sheet of plastic wrap the size of Chicago without getting any air bubbles in it,” said Jiwoong Park, a UChicago professor in the Department of Chemistry, the Institute for Molecular Engineering and the James Franck Institute, who led the study. “When the material itself is just atoms thick, every little stray atom is a problem. We expect this new method to accelerate the discovery of novel materials, as well as enabling large-scale manufacturing,” Park said.

Mathematical model helps explain animals’ decision-making process.

The C. elegans roundworm sees by eating, sucking in big gulps of bacteria to learn about its surrounding environment. As researchers watched, they noticed an odd pattern marked by “bursts” of eating.

JFI researchers including the Dinner group develeoped a mathematical model to explain such eating bursts. The findings, published Aug. 10 in Proceedings of the National Academy of Sciences, help inform a broader understanding of animals’ feeding behavior and the science of decision-making.

“It’s an interesting model for understanding the processes that underlie how animals decide where and when to eat,” said lead author Monika Scholz, a Howard Hughes Medical Institute international student research fellow with UChicago’s Biophysical Sciences program and now at Princeton University. “For these worms, it’s all about the balance between speed and accuracy.”

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Clever experiment documents multi-scale fluid dynamics.

The new findings, published Aug. 3 in Science, are the first to show that helicity maintains a constant value during the flow of viscous fluids. Vortex dynamics have important applications in everyday life; meteorologists, for example, view helicity as a factor that contributes to the formation of supercell tornadoes.

“The fact that we have some measurements for the first time that show helicity can be preserved, especially in the presence of stretching, can translate directly to those efforts,” said William Irvine, an Associate Professor of Physics in the James Franck Institute, who published the findings along with four co-authors.

Simulating helicity in those flows has been difficult because of the widely separated yet interconnecting scales in which they operate. Previous work had been largely theoretical and involved hypothetical, simpler fluids totally lacking in viscosity. Calculations showed that helicity was conserved in these hypothetical fluids, but viscosity emerged as a significant factor in the flow of actual fluids.

“One of the core problems is that you need to sample or measure features of the flow that exist on very different length scales,” said Martin Scheeler, the study’s lead author, who recently completed his Doctorate in Physics in the JFI. The scales range from the diameter of a vortex (approximately 30 centimeters or one foot) to the diameter of its thin core (approximately one milllimeter or three hundredths of an inch).

“You need to measure the flow inside the core as well as the overall shape evolution of that vortex,” Irvine said. “That’s quite a separation.” Irvine characterized Scheeler’s work in overcoming the experimental challenges— simultaneously tracking the fine details of the flow while still measuring the critical larger-scale dynamics—as “a tour de force.”

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New method promises easier nanoscale manufacturing.

The new research, published in Science, is expected to make such materials easily available for eventual use in everything from LED displays to cellular phones to photodetectors and solar cells. Though nanomaterials are promising for future devices, ways to build them into complex structures have been limited and small-scale.

“This is a step needed to move quantum dots and many other nanomaterials from proof-of-concept experiments to real technology we can use,” said co-author Dmitri Talapin, Professor of Chemistry in the James Franck Institute and Scientist with the Center for Nanoscale Materials at Argonne. “It really expands our horizons.”

The new technique, called DOLFIN, makes different nanomaterials directly into “ink” in a process that bypasses the need to lay down a polymer stencil. Talapin and his team carefully designed chemical coatings for individual particles. These coatings react with light, so if you shine light through a patterned mask, the light will transfer the pattern directly into the layer of nanoparticles below—wiring them into useful devices.

“We found the quality of the patterns was comparable to those made with state-of-the-art techniques,” said lead author Yuanyuan Wang, postdoctoral researcher in the Talapin group. “It can be used with a wide range of materials, including semiconductors, metals, oxides or magnetic materials—all commonly used in electronics manufacturing.”

The team is working toward commercializing the DOLFIN technology in partnership with UChicago’s Polsky Center for Entrepreneurship and Innovation.

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Implications for universality.

New research by physicists at the University of Chicago settles a longstanding disagreement over the formation of exotic quantum particles known as Efimov molecules. The findings, published last month in Nature Physics, address differences between how theorists say Efimov molecules should form and the way researchers say they did form in experiments. The study found that the simple picture scientists formulated based on almost 10 years of experimentation had it wrong—a result that has implications for understanding how the first complex molecules formed in the early universe and how complex materials came into being.

“I have to say that I am surprised,” Chin said. “This was an experiment where I did not anticipate the result before we got the data.”

The data came from extremely sensitive experiments done with cesium and lithium atoms using techniques devised by Jacob Johansen, previously a graduate student in Chin’s lab who is now a postdoctoral fellow at Northwestern University. Krutik Patel, a graduate student at UChicago, and Brian DeSalvo, a postdoctoral researcher at UChicago, also contributed to the work.

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Undergraduates in Chin group lead breakthrough work.

Third-year Frankie Fung and fourth-year Mykhaylo Usatyuk led a team of UChicago researchers who demonstrated how to levitate a variety of objects—ceramic and polyethylene spheres, glass bubbles, ice particles, lint strands and thistle seeds—between a warm plate and a cold plate in a vacuum chamber.

“They made lots of intriguing observations that blew my mind,” said Cheng Chin, professor of physics, whose ultracold lab in the Gordon Center for Integrative Science was home to the experiments.

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Collaborative work by the Dinner, Rice, and Scherer groups

The newly developed SPIFF (single-pixel interior filling function) method provides a way to detect and correct systematic errors in data and image analysis used in many areas of science and engineering.

“Anyone working with imaging data on tiny objects — or objects that appear tiny — who wants to determine and track their positions in time and space will benefit from the single-pixel interior filling function method,” said co-principal investigator Norbert Scherer.

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Ultracold atoms unveil a universal symmetry of systems crossing continuous phase transitions.

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The Schuster Group has integrated trapped electrons with superconducting quantum circuits.

“A key aspect of this experiment is that we have integrated trapped electrons with more well-developed superconducting quantum circuits,” said graduate student Ge Yang, lead author of the Physical Review X paper that reported the group’s findings. The team captured the electrons by coaxing them to float above the surface of liquid helium at extremely low temperatures.

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