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Third Annual Fundamentals of Quantum Materials Winter School

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Category: Department News
Published: Thursday, January 10 2019 09:26

FQMWinterSchool2019 smallThe University of Maryland Department of Physics will host the third annual Fundamentals of Quantum Materials Winter School and Workshop January 14th to the 18th at the University of Maryland. 

The Fundamentals of Quantum Materials Winter School and Workshop is an annual event unique to North America, dedicated specifically to the synthesis, characterization and electronic modeling of quantum materials. The FQM Winter School is aimed at providing fundamental training to our current and future generations of Quantum Materials scientists in synthesis and characterization techniques, bringing together senior and junior scientists to address topics at the forefront of current research into quantum materials, while also providing pedagogical background and practical training for junior scientists. With an interdisciplinary and diverse crowd including physicists, chemists, and materials scientists, participants gain a basic functional knowledge of how to plan and carry out synthesis relevant to the study of quantum materials, and experience a unique opportunity to interact with some of the top researchers in the field while networking with fellow peers. The structure of the school includes mornings of pedagogical lectures by ten of the nation's top practicing quantum materials scientists, with afternoons devoted to practical demonstrations in laboratories in the University of Maryland's Center for Nanophysics and Advanced Materials. The school also includes a poster session attended by senior scientists. The FQM Workshop, following the school event, covers current top research on quantum materials, focusing on synthesis, characterization and computational approaches to research of quantum materials such as superconductors, strongly correlated electron systems and topological materials.

For more information, visit the Fundamentals of Quantum Materials Winter School and Workshop homepage.

Cold Atoms Offer a Glimpse of Flat Physics

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Category: Research News
Published: Monday, January 07 2019 09:45

These days, movies and video games render increasingly realistic 3-D images on 2-D screens, giving viewers the illusion of gazing into another world. For many physicists, though, keeping things flat is far more interesting.

One reason is that flat landscapes can unlock new movement patterns in the quantum world of atoms and electrons. For instance, shedding the third dimension enables an entirely new class of particles to emerge—particles that that don’t fit neatly into the two classes, bosons and fermions, provided by nature. These new particles, known as anyons, change in novel ways when they swap places, a feat that could one day power a special breed of quantum computer.

But anyons and the conditions that produce them have been exceedingly hard to spot in experiments. In a pair of papers published this week in Physical Review Letters, JQI Fellow Alexey Gorshkov and several collaborators proposed new ways of studying this unusual flat physics, suggesting that small numbers of constrained atoms could act as stand-ins for the finicky electrons first predicted to exhibit low-dimensional quirks.

"These two papers add to the growing literature demonstrating the promise of cold atoms for studying exotic physics in general and anyons in particular," Gorshkov says. "Coupled with recent advances in cold atom experiments—including by the grougorshkov anyon 1aSimulated images from two papers showing anyons spreading preferentially to the left in a 1-D grid (left) and a novel phase of matter that may arise from atoms constrained to move in 2-D (right). (Images courtesy of the authors)p of Ian Spielman at JQI—this work hints at exciting experimental demonstrations that might be just around the corner."

In the first paper, which was selected as an Editors’ Suggestion, Gorshkov and colleagues proposed looking for a new experimental signature of anyons—one that might be visible in a small collection of atoms hopping around in a 1-D grid. Previous work suggested that such systems might simulate the swapping behavior of anyons, but researchers only knew of ways to spot the effects at extremely cold temperatures. Instead, Fangli Liu, a graduate student at JQI, along with Gorshkov and other collaborators, found a way to detect the presence of anyons without needing such frigid climes.

Ordinarily, atoms spread out symmetrically over time in a 1-D grid, but anyons will generally favor the left over the right or vice versa. The researchers argued that straightforward changes to the laser used to create the grid would make the atoms hop less like themselves and more like anyons. By measuring the way that the number of atoms at different locations changes over time, it would then be possible to spot the asymmetry expected from anyons. Furthermore, adjusting the laser would make it easy to switch the favored direction in the experiment.

"The motivation was to use something that didn’t require extremely cold temperatures to probe the anyons," says Liu, the lead author of the paper. "The hope is that maybe some similar ideas can be used in more general settings, like looking for related asymmetries in two dimensions."

In the second paper, Gorshkov and a separate group of collaborators found theoretical evidence for a new state of matter closely related to a Laughlin liquid, the prototypical example of a substance with topological order. In a Laughlin liquid, particles—originally electrons—find elaborate ways of avoiding one another, leading to the emergence of anyons that carry only a fraction of the electric charge held by an electron.

"Anyons are pretty much still theoretical constructs," says Tobias Grass, a postdoctoral researcher at JQI and the lead author of the second paper, "and experiments have yet to conclusively demonstrate them."

Although fractional charges have been observed in experiments with electrons, many of their other predicted properties have remained unmeasurable. This makes it hard to search for other interesting behavior or to study Laughlin liquids more closely. Grass, Gorshkov and their colleagues suggested a way to manipulate the interactions between a handful of atoms and discovered a new state of matter that mixes characteristics of the Laughlin liquid and a less exotic crystal phase.

The atoms in this new state avoid one another in a similar way as electrons in a Laughlin liquid, and they also fall into a regular pattern like in a crystal—albeit in a strange way, with only half of an atom occupying each crystal site. It’s a unique mix of crystal symmetry and more complex topological order—a combination that has received little prior study.

"The idea that you have a bosonic or fermionic system, and then from interactions there emerges completely different physics—that’s only possible in lower dimensions," Grass says. "Having an experimental demonstration of any of these phases is just interesting from a fundamental perspective."

Story by Chris Cesare

 
Reference Publication
"Asymmetric Particle Transport and Light-Cone Dynamics Induced by Anyonic Statistics," Fangli Liu, James R. Garrison, Dong-Ling Deng, Zhe-Xuan Gong, Alexey V. Gorshkov, Phys. Rev. Lett., 121, 250404 (2018)
"Fractional Quantum Hall Phases of Bosons with Tunable Interactions: From the Laughlin Liquid to a Fractional Wigner Crystal," Tobias Graß, Przemyslaw Bienias, Michael J. Gullans, Rex Lundgren, Joseph Maciejko, Alexey V. Gorshkov, Phys. Rev. Lett., 121, 253403 (2018)
Research Contact: Alexey Gorshkov, This email address is being protected from spambots. You need JavaScript enabled to view it.; Tobias Grass, This email address is being protected from spambots. You need JavaScript enabled to view it.; Fangli Liu, This email address is being protected from spambots. You need JavaScript enabled to view it.
Media Contact: Chris Cesare, This email address is being protected from spambots. You need JavaScript enabled to view it.

Researchers Measure Casimir Torque for the First Time

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Category: Research News
Published: Thursday, December 20 2018 14:03

Casimir crop

Physics researchers and members of the Institute for Research in Electronics and Applied Physics worked with the Department of Electrical and Computer Engineering to measure for the first time an effect that was predicted more than 40 years ago, called the Casimir torque. 

When placed together in a vacuum less than the diameter of a bacterium (one micron) apart, two pieces of metal attract each other. This is called the Casimir effect. The Casimir torque—a related phenomenon that is caused by the same quantum electromagnetic effects that attract the materials—pushes the materials into a spin. Because it is such a tiny effect, the Casimir torque has been difficult to study. The research team, which includes members from UMD's departments of electrical and computer engineering and physics and Institute for Research in Electronics and Applied Physics, has built an apparatus to measure the decades-old prediction of this phenomenon and published their results in the December 20th issue of the journal Nature.

"This is an interesting situation where industry is using something because it works, but the mechanism is not well-understood," said Jeremy Munday, the leader of the research. "For LCD displays, for example, we know how to create twisted liquid crystals, but we don't really know why they twist. Our study proves that the Casimir torque is a crucial component of liquid crystal alignment. It is the first to quantify the contribution of the Casimir effect, but is not the first to prove that it contributes."

The device places a liquid crystal just tens of nanometers from a solid crystal. With a polarizing microscope, the researchers then observed how the liquid crystal twists to match the solid's crystalline axis.

The team used liquid crystals because they are very sensitive to external forces and can twist the light that passes through them. Under the microscope, each imaged pixel is either light or dark depending on how twisted the liquid crystal layer is. In the experiment, a faint change in the brightness of a liquid crystal layer allowed the research team to characterize the liquid crystal twist and the torque that caused it.

The Casimir effect could make nanoscale parts move and can be used to invent new nanoscale devices, such as actuators or motors.

"Think of any machine that requires a torque or twist to be transmitted: driveshafts, motors, etc.," said Munday. "The Casimir torque can do this on a nanoscale."

Knowing the amount of Casimir torque in a system can also help researchers understand the motions of nanoscale parts powered by the Casimir effect.

The team tested a few different types of solids to measure their Casimir torques, and found that each material has its own unique signature of Casimir torque.

The measurement devices were built in UMD's Fab Lab, a shared user facility and cleanroom housing tools to make nanoscale devices.

In the past, the researchers also made the first measurements of a repulsive Casimir force and a measurement of the Casimir force between two spheres. They have also made some predictions that could be confirmed if the current measurement technique can be refined; Munday reports they are testing other materials to control and tailor the torque.

Munday is an associate professor of electrical and computer engineering in UMD's A. James Clark School of Engineering, and his lab is housed in UMD's Institute for Research in Electronics and Applied Physics, which enables interdisciplinary research between its natural science and engineering colleges.

"Experiments like this are helping us better understand and control the quantum vacuum. It's what one might call 'the physics of empty space,' which upon closer examination seems to be not so empty after all," said John Gillaspy, the physics program officer who oversaw National Science Foundation funding of the research.

"Classically, the vacuum is really empty—it is, by definition, the absence of anything," said Gillaspy. "But quantum physics predicts that even the most empty space that one can imagine is filled with 'virtual' particles and fields, quantum fluctuations in pure emptiness that lead to subtle, but very real, effects that can be measured and even exploited to do things that would otherwise be impossible. The universe contains many complicated things, yet there are still unanswered questions about some of the simplest, most fundamental phenomena—this research may help us to find some of the answers."

 Original story: https://energy.umd.edu/news/story/researchers-make-liquid-crystals-do-the-twist

Sankar Das Sarma and Ian Spielman Named 2018 Highly Cited Researchers

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Category: Department News
Published: Wednesday, December 05 2018 11:53

Sankar Das Sarma and Ian Spielman join six other faculty members in the University of Maryland’s College of Computer, Mathematical, and Natural Sciences included on Clarivate Analytics’ 2018 list of Highly Cited Researchers, a compilation of influential names in science.

Sankar Das Sarma is a Richard E. Prange Chair and Distinguished University Professor in Physics, Joint Quantum Institute Fellow, and Condensed Matter Theory Center Director. Das Sarma was included in all previous compilations of this list in 2017, 2016, 2015, 2014 and 2001.

Ian Spielman is an Adjunct Professor of Physics, JQI Fellow and National Institute of Standards and Technology (NIST) Fellow. Spielman was also included in the 2017 compilation.

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