Eno Elected AAAS Fellow

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

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.

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.

Enhancing Simulations of Curved Space with Qubits

One of the mind-bending ideas that physicists and mathematicians have come up with is that space itself—not just objects in space—can be curved. When space curves (as happens dramatically near a black hole), sizes and directions defy normal intuition. Something as straightforward as defining a straight line requires careful consideration.

Understanding curved spaces is important to expanding our knowledge of the universe, but it is fiendishly difficult to study curved spaces in a lab setting (even using simulations). A previous collaboration between researchers at JQI explored using labyrinthine circuits made of superconducting resonators to simulate the physics of certain curved spaces (see the previous story for additional background information and motivation of this line of research). In particular, the team looked at hyperbolic lattices that represent spaces—called negatively curved spaces(link is external)—that have more space than can fit in our everyday “flat” space. Our three-dimensional world doesn’t even have enough space for a two-dimensional negatively curved space.

Now, in a paper published in the journal Physical Review Letters(link is external) on Jan. 3, 2022, the same collaboration between the groups of Alicia Kollár and Alexey Gorshkov expands the potential applications of the technique to include simulating more intricate physics. They’ve laid a theoretical framework for adding qubits—the basic building blocks of quantum computers—to serve as matter in a curved space made of a circuit full of flowing microwaves. Specifically, they considered the addition of qubits that change between two quantum states when they absorb or release a microwave photon—an individual quantum particle of the microwaves that course through the circuit.(Left image) Microwave photons that create an interaction between pairs of qubits (black dots on the edge) in a hyperbolic space are most likely to travel along the shortest path (dotted line). In both images, the darker colors show where photons are more likely to be found. (Right image) A quantum state formed by a qubit (grey dot containing parallel black lines) and an attached microwave photon that can be found at one of the intersections of the grid representing a curved space. (Credit: Przemyslaw Bienias/JQI)(Left image) Microwave photons that create an interaction between pairs of qubits (black dots on the edge) in a hyperbolic space are most likely to travel along the shortest path (dotted line). In both images, the darker colors show where photons are more likely to be found. (Right image) A quantum state formed by a qubit (grey dot containing parallel black lines) and an attached microwave photon that can be found at one of the intersections of the grid representing a curved space. (Credit: Przemyslaw Bienias/JQI)

“This is a new frontier in tabletop experiments studying effects of curvature on physical phenomena,” says first author Przemyslaw Bienias, a former Joint Quantum Institute (JQI) assistant research scientist who is now working for Amazon Web Services as a Quantum Research Scientist. “Here we have a system where this curvature is huge and it's very exciting to see how it influences the physics.”

For researchers to use these simulations they need a detailed understanding of how the simulations represent a curved space and even more importantly under what situations the simulation fails. In particular, the edges that must exist on the physical circuits used in the simulations must be carefully considered since scientists are often interested in an edgeless, infinite curved space. This is especially important for hyperbolic lattices because they have nearly the same number of sites on the edge of the lattice as inside. So the team identified situations where the circuits should reflect the reality of an infinite curved space despite the circuit’s edge and situations where future researchers will have to interpret results carefully.

The team found that certain properties, like how likely a qubit is to release a photon, shouldn’t be dramatically impacted by the circuit’s edge. But other aspects of the physics, like the proportion of states that photons occupy at a given shared total energy, will be strongly influenced by the edge.

With proper care, this type of simulation will provide a peek into how negatively curved spaces are a foundation for an entirely new world of physics.

“In this paper, we asked the question, ‘What happens when you add qubits to the photons living on those hyperbolic lattices?’” Bienias says. “We are asking, ‘What type of physics emerges there and what type of interactions are possible?’”

The researchers first looked at how the microwaves and a single qubit in the circuit can combine. The team predicts that the size of special quantum states in which a photon is attached to a particular qubit—a bound state—will be limited by the curved space in a way that doesn’t happen in flat space. The right-side image above shows such a state with the darker coloring showing where the photon is most likely to be found around the qubit represented by the grey dot.

They then investigated what happens when there are multiple qubits added to a circuit full of microwaves. The photons traveling between qubits serve as intermediaries and allow the qubits to interact. The team’s analysis suggests that the photons that are causing qubits to interact tend to travel along the shortest path between the two points in the circuit—corresponding to the shortest distance in the simulated curved space. One of these paths through the curved space is shown in the left-side image above. This result matches physicists’ current expectations of such a space and is a promising sign that the simulations will reveal useful results in more complex situations.

Additionally, the researchers predict that the curvature will limit the range of the interactions between qubits similar to the way it limits the size of the individual bound states. Simulations using this setup could allow scientists to explore the behaviors of many particles interacting in a curved space, which is impractical to study using brute numerical calculation.

These results build upon the previous research and provide additional tools for exploring new physics using superconducting circuits to simulate curved space. The inclusion of interactions explored in this paper could aid in using the simulations to investigate the topic called AdS/CFT correspondence that combines theories of quantum gravity and quantum field theories.

“Hyperbolic connectivity is immensely useful in classical computation, underlying, for example, some of the most efficient classical error correcting codes in use today,” Kollár says. “We now know that adding qubits to a hyperbolic resonator lattice will endow the qubits’ interactions with hyperbolic structure, rather than the native flat curvature of the lab. This opens the door to allow us to carry out direct experiments to examine the effect of hyperbolic connectivity on quantum bits and quantum information.”

Original story by Bailey Bedford: https://jqi.umd.edu/news/enhancing-simulations-curved-space-qubits

In addition to Kollár, Gorshkov and Bienias, other co-authors of the paper were Ron Belyansky, a JQI physics graduate student, and Igor Boettcher, a former JQI postdoctoral researcher and current assistant professor at the University of Alberta.