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Kollár Awarded Sloan Research Fellowship

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Category: Department News
Published: Tuesday, February 15 2022 10:01

Assistant Professor Alicia Kollár has been awarded a prestigious 2022 Sloan Research Fellowship. This award is given to early career researchers by the Alfred P. Sloan Foundation to recognize distinguished performance and the potential to make substantial contributions to their field. Each fellowship provides $75,000 to support the fellow’s research over two years.

Kollár will use the fellowship to support her research into creating new synthetic materials that are designed using quantum physics and applied mathematics. These synthetic materials can reveal physics that is difficult or impossible to observe in traditional materials.

“What really excites me about this award is to see support for the more interdisciplinary side of my research,” Kollár says. “My original background is in quantum physics and that's been where my grant support has come from so far, but this Sloan award is focused on looking at questions at the intersection of math and physics.”Alicia Kollár Alicia Kollár

This line of Kollár’s research uses mathematical tools based on the field of graph theory—the study of relationships between objects (in terms of a “graph” made of “vertices” that are connected by “edges”). Researchers use the tools to produce stripped down descriptions of materials in terms of just nodes and their connections—like if there is a connection where electrons can hop between specific points in a material. These descriptions don’t care about the exact distance between atoms or molecules or their precise orientation relative to each other but only about what connections exist between points. This approach is useful for identifying overarching features of different types of materials and is especially helpful in sorting out which material properties are derived from the basic connections being investigated, as opposed to those related to the quirks of a material’s particular components.

This mathematical perspective allows researchers, like Kollár, to design abstract connections that should produce unique properties, but it isn’t easy to then translate the idea on a page into a material that has the exact desired connections. Going from pure math to a real material is much harder than the reverse process of stripping details away from a well-studied material; to do so requires the exhaustive work of recognizing and juggling all the idiosyncrasies of real chemistry. The details of all the possible choices of atoms and how they interact and arrange themselves makes matching the elegant mathematical design to a physical material prohibitively challenging.

So instead Kollár has focused on synthetic materials made of circuits of resonators and superconducting qubits that house traveling microwaves. These circuits easily recreate the flexible connections of graph-theoretic descriptions and can let the complex physics play out, revealing features that current simulations can’t calculate. Essentially, Kollár can custom design the desired connections in a synthetic material and see if the results are interesting instead of going through the hassle of searching for a chemical structure that naturally has the connections every time she wants to do a new experiment. She has even been able to create connections that simulate a negatively curved space—a space impossible to create in the lab because they have “more space” than our normal space.

The insights from these synthetic materials have the potential to reveal new material behaviors and to give researchers a better understanding of how to best use graph-theoretic techniques.

Besides making these synthetic materials she is also working to push the mathematical side of this approach, including identifying new mathematical rules that govern one dimensional graphs that might provide insights into codes used in quantum computing.

 “This Sloan Fellowship will give my group the opportunity to really dig in to optimizing how synthetic materials are made in order to make them as versatile a tool as possible,” Kollár says.

The Sloan fellowships are awarded to untenured teaching faculty who work in the fields of chemistry, computer science, Earth system science, economics, mathematics, neuroscience, physics, or a related field. Candidates are nominated by their colleagues, and then fellows are selected by an independent committee of researchers in the relevant field based on the candidates’ “independent research accomplishments, creativity, and potential to become leaders in the scientific community through their contributions to their field,” according to the Sloan website. Other UMD winners this year are Lei Chen of mathematics and Pratyush Tiwary of chemistry/biochemisty and IPST. 

“Today’s Sloan Research Fellows represent the scientific leaders of tomorrow,” says Adam F. Falk, president of the Alfred P. Sloan Foundation. “As formidable young scholars, they are already shaping the research agenda within their respective fields—and their trailblazing won’t end here.”

 

Original story by Bailey Bedford: https://jqi.umd.edu/news/jqi-fellow-kollar-awarded-sloan-research-fellowship

Eno Elected AAAS Fellow

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Category: Department News
Published: Wednesday, January 26 2022 00:53

Sarah Eno has been named a Fellow of the American Association for the Advancement of Science (AAAS). Election is an honor bestowed upon AAAS members by their peers in recognition of distinguished efforts to advance science or its applications.

Eno’s research has focused on precision studies of the properties of the W boson, tests of QCD using Z bosons, and searches for exotic particles predicted by theories of physics beyond the Standard Model. Other efforts have included improvement and simulations of calorimeters to better study the momentums of jets and of missing transverse energy, and studies of radiation damage in plastic scintillators.

Eno was cited by the AAAS for leadership and research in both detector and analysis development, enabling the discovery of the top quark and Higgs boson, and the search for new phenomena at high energy colliders.

"I am truly humbled that AAAS has decided my accomplishments are worthy of this honor," Eno said. "My work was enabled by the wonderful collaborations in which I worked and my wonderful colleagues and students here at U. Maryland.”Sarah EnoSarah Eno

Eno received her bachelor's degree from Gettysburg College and her Ph.D. from the University of Rochester for work on the AMY experiment in Tsukuba, Japan. She then accepted a post-doctoral appointment at the University of Chicago Enrico Fermi Institute, working on the CDF experiment. In 1993, Dr. Eno joined the University of Maryland as an Assistant Professor, and moved to the DØ experiment at Fermilab.  The discovery of the top quark—announced by the CDF and DØ teams in 1995—was a milestone in particle physics. Eno’s precise measurement of the decay width and mass of the electroweak W boson helped predict the mass of the top quark.

Since 1999, Eno has worked on the Compact Muon Solenoid (CMS) experiment of the Large Hadron Collider at CERN. In 2012, CERN announced experimental verification of the Higgs boson, and the 2013 Nobel Prize in Physics was awarded to François Englert and Peter W. Higgs, whose 1960s calculations determined that mass could not exist without the presence of such a particle.  Since 2020 she is also participating in the development of experiments for a potential new electron-positron collider at CERN (FCC-ee).

Eno’s accolades include selection as an Outstanding Junior Investigator by the U.S. Department of Energy in 1995 and an Alumni Achievement Award from Gettysburg College in 1999. She is a Fellow of the American Physical Society (APS) and a University of Maryland Distinguished Scholar-Teacher.  She has also been cited by the APS as an Outstanding Referee for exceptional work in the assessment of manuscripts.

“Sarah Eno is widely known as a leader in high energy physics, and this recognition from the AAAS befits her extensive career achievements,” said Steve Rolston, chair of the University of Maryland Department of Physics.

The honor of being elected a Fellow of AAAS began in 1874 and is acknowledged with a certificate and rosette, presented at the annual Fellows Forum at the AAAS Annual Meeting, scheduled this year for February 19. In addition to Eno, physics affiliate professor John B. Kogut, entomology chair Leslie Pick and environmental science and technology chair William Bowerman IV were elected. 

Tug-of-War Unlocks Menagerie of Quantum Phases of Matter

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Category: Research News
Published: Tuesday, January 25 2022 02:46
Phases are integral to how we define our world. We navigate through the phases of our lives, from child to teenager to adult, chaperoned along the way by our changing traits and behaviors. Nature, too, undergoes phase changes. Lakes can freeze for the winter, thaw in the spring and lose water to evaporation in the dog days of summer. It’s useful to capture and study the differences that accompany these dramatic shifts.
 

In physics, phases of matter play a key role, and there are more phases than just the familiar solid, liquid and gas. Physicists have built a modest taxonomy of the different phases that matter can inhabit, and they’ve explored the alchemy of how one phase can be converted into another. Now, scientists are discovering new ways to conjure up uniquely quantum phases that may be foundational to quantum computers and other quantum tech of the future.

“There's a whole world here,” says Associate Professor Maissam Barkeshli, a  Fellow of the Joint Quantum Institute and a member of the Condensed Matter Theory Center. “There’s a whole zoo of phases that we could study by having competing processes in random quantum circuits.”In new numerical experiments, quantum particles (black dots), which travel upward through time, are subject to random quantum processes (blue, green and yellow blocks). Depending on the likelihood of the different kinds of processes, the quantum particles ultimately end up in different entanglement phases. This figure shows five examples of randomly chosen processes acting on a small number of particles. (Credit: A. Lavasani/JQI)In new numerical experiments, quantum particles (black dots), which travel upward through time, are subject to random quantum processes (blue, green and yellow blocks). Depending on the likelihood of the different kinds of processes, the quantum particles ultimately end up in different entanglement phases. This figure shows five examples of randomly chosen processes acting on a small number of particles. (Credit: A. Lavasani/JQI)

Often when physicists study phases of matter they examine how a solid slab of metal or a cloud of gas changes as it gets hotter or colder. Sometimes the changes are routine—we’ve all boiled water to cook pasta and frozen it to chill our drinks. Other times the transformations are astonishing, like when certain metals get cold enough to become superconductors(link is external) or a gas heats up and breaks apart into a glowing plasma soup(link is external).

However, changing the temperature is only one way to transmute matter into different phases. Scientists also blast samples with strong electric or magnetic fields or place them in special chambers and dial up the pressure. In these experiments, researchers are hunting for a stark transition in a material’s behavior or a change in the way its atoms are organized.

In a new paper published recently in the journal Physical Review Letters(link is external), Barkeshli and two colleagues continued this tradition of exploring how materials respond to their environment. But instead of looking for changes in conductivity or molecular structure, they focused on changes in a uniquely quantum property: entanglement, or the degree to which quantum particles give up their individuality and become correlated with each other. The amount of entanglement and the distinct way that it spreads out among a group of particles defines different entanglement phases.

In all the entanglement phases studied in the new paper, the particles are fixed in place. They don’t move around and form new links, like what happens when ice melts into water. Instead, transitioning from phase to phase requires a metamorphosis in the way that the particles are entangled with each other—a change that’s invisible if you only pay attention to the local behavior of the particles and their links. To reveal this change, the researchers used a quantity called the topological entanglement entropy, which captures, in a single number, the amount of entanglement present in a collection of particles. Different entanglement phases have different amounts of entanglement entropy, so calculating this number picks out which entanglement phase the particles are in.

The researchers used UMD’s supercomputers to conduct numerical experiments and study the entanglement phases of a grid of quantum particles. They studied which entanglement phase the particles end up in when subjected to a tug-of-war between three competing quantum processes. One process performs a quantum measurement on an individual particle, forcing it to choose between one of two states and removing some entanglement from the grid. Another process, which the researchers were the first to include, is also a quantum measurement, but instead of measuring a single particle it measures four neighboring particles at a time. This, too, removes some entanglement, but it can also spread entanglement in a controlled way. The final process twists and spins the particles around, like what happens when a magnet influences a compass needle. This tends to inject more entanglement into the grid.

On their own, each of the three processes will pull the particles into three different entanglement phases. After many applications of the process that twists the particles around, entanglement will be spread far and wide—all the particles will end up entangled with each other. The single particle measurements have the opposite effect: They remove entanglement and halt its spread. The four-particle measurements, which spread entanglement in a controlled way, lead to an in-between phase.

The researchers began their numerical experiments by preparing all the particles in the same way. Then, they randomly selected both a process and which cluster of particles it was applied to. After many rounds of random applications, they ceased their prodding and calculated the topological entanglement entropy. Over many runs, the researchers also varied the likelihood of selecting the different processes, tuning how often each of the processes gets applied relative to the others. By performing these experiments many times, the researchers constructed a phase diagram—basically a map of how much entanglement is left after many rounds of random quantum nudges.

The results add to an emerging body of work that studies the effects of applying random quantum processes—including a paper published in Nature Physics earlier this year(link is external) by the same team—but the inclusion of the four-particle measurements in the new result produced a richer picture. In addition to some expected features, like three distinct entanglement phases corresponding to the three processes, the researchers found a couple of surprises.

In particular, they found that entanglement spread widely throughout the system using only the two quantum measurement processes, even though neither process would produce that phase on its own. They may have even spotted a stable phase perched between the phase created by the single-particle measurements alone and the phase created by the four-particle measurements alone, an unlikely phenomenon akin to balancing something on the edge of a knife.

But besides creating the phase diagram itself, the authors say that their technique supplies a new way to prepare phases that are already well known. For instance, the phase created by the four-particle measurements is key to quantum error correcting codes and topological quantum computation. One way of preparing this phase would require making the four-particle measurements, interpreting the results of those measurements, and feeding that information back into the quantum computer by performing additional highly controlled quantum procedures. To prepare the same phase with the new technique, the same four-particle measurements still must be made, but they can be done in a random fashion, with other quantum processes interspersed, and there is no need to interpret the results of the measurements—a potential boon for researchers looking to build quantum devices.

“It is a kind of shortcut in the sense that it's a way of realizing something interesting without needing as much control as you thought you needed,” Barkeshli says.

The authors note that the new work also contributes to the growing study of non-equilibrium phases of quantum matter, which includes exotic discoveries like time crystals and many-body localization. These contrast with equilibrium phases of matter in which systems exchange heat with their environment and ultimately share the same temperature, settling down into stable configurations. The key difference between equilibrium and non-equilibrium phases is the continual nudges that the application of random processes provides.

"Our work shows that the peculiar nature of measurements in quantum mechanics could be leveraged into realizing exotic non-equilibrium phases of matter,” says Ali Lavasani, a graduate student in the UMD Department of Physics and the first author of the new paper. “Moreover, this technique might also lead to novel non-equilibrium phases of matter which do not have any counterpart in equilibrium settings, just like driven systems give rise to time crystals that are forbidden in equilibrium systems.”

Original story by Chris Cesare: https://jqi.umd.edu/news/tug-war-unlocks-menagerie-quantum-phases-matter

In addition to Barkeshli and Lavasani, the paper had one additional author: Yahya Alavirad, a former graduate student in physics at the University of Maryland who is now a postdoctoral scholar in physics at the University of California San Diego.

Reference Publication: "Topological Order and Criticality in (2+1)D Monitored Random Quantum Circuits," Ali Lavasani, Yahya Alavirad, Maissam Barkeshli, Phys. Rev. Lett., 127, 235701 (2021)
 
Research Contacts: Maissam Barkeshli This email address is being protected from spambots. You need JavaScript enabled to view it.; Ali Lavasani This email address is being protected from spambots. You need JavaScript enabled to view it.

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