Joint Quantum Institute

Congratulations to Montgomery Blair High School senior Jason Youm! He placed in the top dozen competitors in the physics and astronomy category at the Regeneron International Science and Engineering Fair (ISEF).
The Regeneron ISEF brings together high school students from across the world. The competitors must earn their spot by first succeeding at an affiliated local science fair. In the competition, Youm presented research that he performed during the summer of 2023 under the mentorship of JQI Fellow Alexey Gorshkov and JQI graduate student Joseph Iosue. In his project, Youm performed calculations to help researchers investigate how certain tasks can be performed significantly faster by quantum computers than their traditional counterparts.
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Quantum particles have unique properties that make them powerful tools, but those very same properties can be the bane of researchers. Each quantum particle can inhabit a combination of multiple possibilities, called a quantum superposition, and together they can form intricate webs of connection through quantum entanglement.

These phenomena are the main ingredients of quantum computers, but they also often make it almost impossible to use traditional tools to track a collection of strongly interacting quantum particles for very long. Both human brains and supercomputers, which each operate using non-quantum building blocks, are easily overwhelmed by the rapid proliferation of the resulting interwoven quantum possibilities. In nuclear and particle physics, as well as many other areas, the challenges involved in determining the fate of quantum interactions and following the trajectories of particles often hinder research or force scientists to rely heavily on approximations. To counter this, researchers are actively inventing techniques and developing novel computers and simulations that promise to harness the properties of quantum particles in order to provide a clearer window into the quantum world.

In an article published earlier this year in the journal Physical Review Letters, Ron Belyansky, Zohreh Davoudi, Alexey Gorshkov and their colleagues, proposed a quantum simulation that might be possible to implement soon. They propose using superconducting circuits to simulate a simplified model of collisions between fundamental particles called quarks and mesons (which are themselves made of quarks and antiquarks). In the paper, the group presented the simulation method and discussed what insights the simulations might provide about the creation of particles during energetic collisions.
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Scientists on the hunt for compact and robust sources of multicolored laser light have generated the first topological frequency comb. Their result, which relies on a small silicon nitride chip patterned with hundreds of microscopic rings, will appear in the June 21, 2024 issue of the journal Science.

Light from an ordinary laser shines with a single, sharply defined color—or, equivalently, a single frequency. A frequency comb is like a souped-up laser, but instead of emitting a single frequency of light, a frequency comb shines with many pristine, evenly spaced frequency spikes. The even spacing between the spikes resembles the teeth of a comb, which lends the frequency comb its name.

The earliest frequency combs required bulky equipment to create. More recently researchers have been focused on miniaturizing them into integrated, chip-based platforms. Despite big improvements in shrinking the equipment needed to generate frequency combs, the fundamental ideas haven’t changed. Creating a useful frequency comb requires a stable source of light and a way to disperse that light into the teeth of the comb by taking advantage of optical gain, loss and other effects that emerge when the source of light gets more intense.

In the new work, JQI Fellow Mohammad Hafezi, who is also a Minta Martin professor of electrical and computer engineering and physics at the University of Maryland (UMD), JQI Fellow Kartik Srinivasan, who is also a Fellow of the National Institute of Standards and Technology, and several colleagues have combined two lines of research into a new method for generating frequency combs. One line is attempting to miniaturize the creation of frequency combs using microscopic resonator rings fabricated out of semiconductors. The second involves topological photonics, which uses patterns of repeating structures to create pathways for light that are immune to small imperfections in fabrication.

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Read more: https://jqi.umd.edu/news/new-photonic-chip-spawns-nested-topological-frequency-comb

Image credit: E. Edwards

Congratulations to JQI Fellow Alexey Gorshkov for winning the 2024 IEEE Photonics Society Quantum Electronics Award! He was honored for his research contributions in the areas of understanding, designing, and controlling interacting quantum systems. These topics are essential to the development and operation of technologies like quantum computers, quantum networks and quantum sensors.
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Computing is in a dynamic and exciting period. Quantum computing is taking its first toddling steps toward delivering practical results. Meanwhile, artificial intelligence remains in public conversation as it’s used for everything from producing faked videos, to writing business emails to generating bespoke images from text prompts. Some physicists are exploring the opportunities that arise when the power of machine learning—a widely used approach in AI research—is brought to bear on quantum physics, and two researchers at JQI have presented new mathematical tools that will help researchers use machine learning to study quantum physics. Using these tools, they have identified new opportunities in quantum research where machine learning can be applied.
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Congratulations to the JQI researchers and their colleagues who won the 2023 UMD Quantum Invention of the Year Award! The university presents this annual award to celebrate all the innovative work produced by researchers on the campus. This year JQI researchers and their colleagues have won in the quantum category for a new method for counting particles of light—photons—without destroying them. Non-destructively counting photons has potential uses in quantum computers and quantum networks that store information in quantum states of light.
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The world is a cluttered, noisy place, and the ability to effectively focus is a valuable skill. Researchers at JQI have identified a new way to focus their attention and obtain useful insights into the way information associated with a configuration of interacting particles gets dispersed and effectively lost over time. Their technique focuses on a single feature that describes how various amounts of energy can be held by different configurations a quantum system. The approach provides insight into how a collection of quantum particles can evolve without the researchers having to grapple with the intricacies of the interactions that make the system change over time.
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Read more: https://jqi.umd.edu/news/focused-approach-can-help-untangle-messy-quantum-scrambling-problems

Humanity’s desire to measure time more and more accurately has been a driving force in technological development, and improved clocks and the innovations behind them have repeatedly delivered unexpected applications and scientific discoveries. For instance, when sailors needed high precision timekeeping to better navigate the open seas, it motivated the development of mechanical clocks. And in turn, more accurate clocks allowed better measurements in astronomy and physics. Now, clocks are inescapable parts of daily life, but the demands of GPS, space navigation and other applications are still motivating scientists to push timekeeping to new extremes.

The best clocks ever made are optical atomic clocks. An atomic clock can be accurate enough that it would have to run for 10 million years to be off by even a second. The National Institute of Standards and Technology (NIST) has been central in the long history of developing atomic clocks and pushing the limits of metrology—the science and practice of making measurements. And NIST researchers are continuing that improve all pieces of an atomic clock, including the clockwork. As part of the clockwork improvement effort, JQI Fellow Kartik Srinivasan, who is also a NIST fellow, and his colleagues have been exploring how light is altered as it races repeatedly around a minuscule track on a chip. In an article published on December 13, 2023, in the journal Nature, the researchers describe a new way to use the devices to make precision measurements of light. The new technique might eliminate the need for several large, energy-hungry components in next-generation optical atomic clocks and other metrology tasks.

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Read more: jqi.umd.edu/news/light-synchronization-technique-heralds-bright-new-chapter-small-atomic-clocks

The researchers and engineers studying quantum technologies are exploring uncharted territory. Due to the unintuitive quirks of quantum physics, the terrain isn’t easy to scout, and the path of progress has been littered with wrong turns and dead ends.

Sometimes, though, theorists have streamlined progress by spotting roadblocks in the distance or identifying the rules of the road. For instance, researchers have found several quantum speed limits—called Lieb-Robinson bounds—that are impassable caps on how quickly information can travel through collections of quantum particles. But to make calculating the limits easier, physicists have mostly neglected the influence of disorder. In the real world, disorder can’t always be ignored, so researchers need to understand its potential effects.

JQI researchers are facing down the impact disorder has on speed limits. In an article published in the journal Physical Review X Quantum, they described novel methods for pulling insights from the mess created by disorder and identified new types of quantum speed limits that apply when disorder is present.
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Matter—all the stuff we see around us—can be classified into familiar phases: our chairs are solid, our coffee is liquid, and the oxygen we breathe is a gas. This grouping obscures the nitty gritty details of what each molecule or atom is up to and reduces all that complexity down to a few main features that are most salient in our everyday lives.

But those are not the only properties of matter that matter. Focusing on solids, physicists have found that they can group things according to symmetries. For example, atoms in solids arrange themselves into repeating patterns, forming crystals that can be grouped according to whether they look the same left and right, up and down, rotated about, and more. In the 1980s, physicists discovered a new paradigm: In addition to symmetries, solids can be classified using topology—a field of math that does for geometrical shapes the same kind of thing that symmetries do for crystalline solids. All the shapes without holes (a ball, a pizza) are in the same topological “phase,” while those with one hole (a donut, a coffee mug) are in a different “phase,” and so on with each new hole.

Within physics, topology doesn’t usually refer to the shape a piece of metal is cut into. Rather, the topology of how electrons are arranged inside a crystal provides information about the material’s electrical conductance and other properties. Now, theorists at the Joint Quantum Institute have found that these same crystals hide a richer set of topological phases than previously thought. In two separate works, they revealed a host of possible topological phases that become apparent when two different kinds of defects develop in crystals, or when they study the twirling properties of the electronic arrangement. They published their findings in the journal Physical Review X on July 14, 2023 and in the journal Physical Review Letters in Dec. 2022.

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Read more: https://jqi.umd.edu/news/crystal-imperfections-reveal-rich-new-phases-familiar-matter

Deepening our understanding of the quantum world and developing new tools to peer into it is a very active area of physics research today. In this crowded field full of diverse theoretical ideas and physical tools, JQI Fellow Nathan Schine has managed to carve out a distinctive space for himself and his lab.

Schine’s research program manipulates the interactions between atoms and photons—the particles that make up light—in novel, well-controlled ways in order to simulate other, harder-to-probe quantum phenomena. To coax the photons into new simulation patterns, Schine is using unique arrangements of mirrors to bounce photons around. He is also strategically placing atoms in the photons’ way with the help of precisely controlled laser beams. To boot, the atoms he is using (ytterbium) have a relatively complex structure, giving Schine extra avenues to explore. He has been able to create this unique niche by combining the experimental expertise he gained from graduate school and postdoctoral research with his theoretical big-picture savvy.

Schine, who is also an assistant professor of physics at UMD and a member of the NSF Quantum Leap Challenge Institute for Robust Quantum Simulation, has been slowly homing in on his academic sweet spot for much of his life. Growing up, his interests were broad—they included science and math, but also history and other areas of the humanities. “It wasn't like I knew from an early age that I was going to go be a physicist,” Schine says.

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Read more: https://jqi.umd.edu/news/nathan-schine-twists-photons-and-cools-atoms-unique-quantum-dance

One of the most exciting applications of quantum computers will be to direct their gaze inwards, at the very quantum rules that make them tick. Quantum computers can be used to simulate quantum physics itself, and perhaps even explore realms that don’t exist anywhere in nature.

But even in the absence of a fully functional, large-scale quantum computer, physicists can use a quantum system they can easily control to emulate a more complicated or less accessible one. Ultracold atoms—atoms that are cooled to temperatures just a tad above absolute zero—are a leading platform for quantum simulation. These atoms can be controlled with laser beams and magnetic fields and coaxed into performing a quantum dance routine choreographed by an experimenter. And it’s also straightforward to peer into their quantum nature using high-resolution imaging to extract information after—or while—they complete their steps.

Now, researchers at JQI and the NSF Quantum Leap Challenge Institute for Robust Quantum Simulation (RQS), led by former JQI postdoctoral fellow Mingwu Lu and graduate student Graham Reid, have coached their ultracold atoms to do a new dance, adding to the growing toolkit of quantum simulation. In a pair of studies, they’ve bent their atoms out of shape, winding their quantum mechanical spins around in both space and time before tying them off to create a kind of space-time quantum pretzel.

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One of the biggest achievements of quantum physics was recasting our vision of the atom. Out was the early 1900s model of a solar system in miniature, in which electrons looped around a solid nucleus. Instead, quantum physics showed that electrons live a far more interesting life, meandering around the nucleus in clouds that look like tiny balloons. These balloons are known as atomic orbitals, and they come in all sorts of different shapes—perfectly round, two-lobed, clover-leaf-shaped. The number of lobes in the balloon signifies how much the electron spins about the nucleus.

That’s all well and good for individual atoms, but when atoms come together to form something solid—like a chunk of metal, say—the outermost electrons in the atoms can link arms and lose sight of the nucleus they came from, forming many oversized balloons that span the whole chunk of metal. They stop spinning about their nuclei and flow through the metal to carry electrical currents, shedding the diversity of multi-lobed balloons.

Now, researchers at the Quantum Materials Center (QMC) at the University of Maryland (UMD), in collaboration with theorists at the Condensed Matter Theory Center (CMTC) and JQI, have produced the first experimental evidence that one metal—and likely others in its class—have electrons that manage to preserve a more interesting, multi-lobed structure as they move around in a solid. They experimentally studied the shape of these balloons and found not a uniform surface, but a complex structure. This unusual metal is not only fundamentally interesting, but it could also prove useful for building quantum computers that are resistant to noise. The researchers published their findings recently in the journal Physical Review Research.

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Read more: https://jqi.umd.edu/news/electrons-take-new-shape-inside-unconventional-metal

Taming rays of light and bending them to your will is tricky business. Light travels fast and getting a good chunk of it to stay in one place for a long time requires a lot of skillful coaxing. But the benefits of learning how to hold a moonbeam (or, more likely, a laser beam) in your hand, or on a convenient chip, are enormous. Trapping and controlling light on a chip can enable better lasers, sensors that help self-driving cars “see,” the creation of quantum-entangled pairs of photons that can be used for secure communication, and fundamental studies of the basic interactions between light and atoms—just to name a few.

Of all the moonbeam-holding chip technologies out there, two stand the tallest: the evocatively named whispering gallery mode microrings, which are easy to manufacture and can trap light of many colors very efficiently, and photonic crystals, which are much trickier to make and inject light into but are unrivaled in their ability to confine light of a particular color into a tiny space—resulting in a very large intensity of light for each confined photon.

Recently, a team of researchers at JQI struck upon a clever way to combine whispering gallery modes and photonic crystals in one easily manufacturable device. This hybrid device, which they call a microgear photonic crystal ring, can trap many colors of light while also capturing particular colors in tightly confined, high-intensity bundles. This unique combination of features opens a route to new applications, as well as exciting possibilities for manipulating light in novel ways for basic research.

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Quantum physics is a notorious rule-breaker. For example, it makes the classical laws of thermodynamics, which describe how heat and energy move around, look more like guidelines than ironclad natural laws.

In some experiments, a quantum object can keep its cool despite sitting next to something hot that is steadily releasing energy. It’s similar to reaching into the oven for a hot pan without a mitt and having your hand remain comfortably cool.

For an isolated quantum object, like a single atom, physicists have a good idea why this behavior sometimes happens. But many researchers suspected that any time several quantum objects got together and started bumping into each other the resulting gang of quantum particles would be too disorganized to pull off this particular violation of the laws of thermodynamics.

A new experiment led by David Weld, an associate professor of physics at the University of California, Santa Barbra (UCSB), in collaboration with JQI Fellow Victor Galitski, shows that several interacting quantum particles can also keep their cool—at least for a time. In a new in the journal Nature Physics, Galitski and the researchers at UCSB describe the experiment, which is the first to explore this behavior, called dynamical localization, with interactions included.
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Future quantum computers may pose a threat to the security of online transactions, but the National Institute of Standards and Technology (NIST) is wrapping up a competition to find new ways of safeguarding digital data. Hear all about it in our latest episode of Relatively Certain!

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https://jqi.umd.edu/news/podcast/quantum-safe-algorithms-face-nists-cryptography-showdown

There is a heated race to make quantum computers deliver practical results. But this race isn't just about making better technology—usually defined in terms of having fewer errors and more qubits, which are the basic building blocks that store quantum information. At least for now, the quantum computing race requires grappling with the complex realities of both quantum technologies and difficult problems. To develop quantum computing applications, researchers need to understand a particular quantum technology and a particular challenging problem and then adapt the strengths of the technology to address the intricacies of the problem.

Theoretical nuclear physicist Zohreh Davoudi, an assistant professor of physics at the University of Maryland (UMD) and a member of the Maryland Center for Fundamental Physics, has been working with multiple colleagues at UMD to ensure that the problems that she cares about are among those benefiting from early advances in quantum computing.

Davoudi and JQI Fellow Norbert Linke are collaborating to push the frontier of both the theories and technologies of quantum simulation through research that uses current quantum computers. Their research is intended to illuminate a path toward simulations that can cut through the current blockade of fiendishly complex calculations and deliver new theoretical predictions.

In a new paper in PRX Quantum, Davoudi, Linke and their colleagues have combined theory and experiment to push the boundaries of quantum simulations—testing the limits of both the ion-based quantum computer in Linke’s lab and proposals for simulating quantum fields.
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Elizabeth Bennewitz, a first-year physics graduate student at JQI and the Joint Center for Quantum Information and Computer Science (QuICS), has received a Department of Energy Computational Science Graduate Fellowship. Bennewitz is one of 33 recipients in 2022—the largest number of students this program has ever selected in a year.
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Physicists sometimes come up with crazy stories that sound like science fiction. Some turn out to be true, like how the curvature of space and time described by Einstein was eventually borne out by astronomical measurements. Others linger on as mere possibilities or mathematical curiosities.

In a new paper in Physical Review Research, JQI Fellow Victor Galitski and JQI graduate student Alireza Parhizkar have explored the imaginative possibility that our reality is only one half of a pair of interacting worlds. Their mathematical model may provide a new perspective for looking at fundamental features of reality—including why our universe expands the way it does and how that relates to the most miniscule lengths allowed in quantum mechanics. These topics are crucial to understanding our universe and are part of one of the great mysteries of modern physics.

The pair of scientists stumbled upon this new perspective when they were looking into research on sheets of graphene—single atomic layers of carbon in a repeating hexagonal pattern.
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There is nothing permanent except change. This is perhaps never truer than in the fickle and fluctuating world of quantum mechanics.

The quantum world is in constant flux. The properties of quantum particles flit between discrete, quantized states without any possibility of ever being found in an intermediate state. How quantum states change defies normal intuition and remains the topic of active debate—for both scientists and philosophers.

The rules governing things like billiards balls and the temperature of a gas look very different from the quantum rules governing things like electron collisions and the energy absorbed or released by a single atom. And there is no known sharp, defining line between these two radically different domains of physical laws. Quantum changes are foundational to our universe and understanding them is becoming increasingly important for practical applications of quantum technologies.

In a recent paper, JQI Fellow Alexey Gorshkov, JQI postdoctoral researcher Luis Pedro García-Pintos and their colleagues provide a new perspective for investigating quantum changes. They developed a mathematical description that sorts quantum behaviors in a system into two distinct parts. One piece of their description looks like the behavior of a quantum system that isn’t interacting with anything, and the second piece looks like the familiar behavior of a classical system. Using this perspective, the researchers identified limits on how quickly quantum systems can evolve based on their general features, and they better describe how those changes relate to changes in non-quantum situations.
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Congratulations to Elizabeth Bennewitz, a first-year physics graduate student at JQI and QuICS, who has been named a finalist for a 2022 Hertz Fellowship. Out of more than 650 applicants, Bennewitz is one of 45 finalists with a chance of receiving up to $250,000 in support from the Fannie and John Hertz Foundation.
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Congratulations to JQI Fellow Alicia Kollár on receiving a 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.
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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 Maissam Barkeshli, a JQI Fellow and physicist at the University of Maryland who is also 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.”

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 or a gas heats up and breaks apart into a glowing plasma soup.

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, 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.

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Read more: https://jqi.umd.edu/news/tug-war-unlocks-menagerie-quantum-phases-matter

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.

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. 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—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 on Jan. 3, 2022, the same collaboration between the groups of JQI Fellows Alicia Kollár and Alexey Gorshkov, who is also Fellow of the Joint Center for Quantum Information and Computer Science, 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.
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Read more: https://jqi.umd.edu/news/enhancing-simulations-curved-space-qubits