Ott Elected Foreign Member of the Academia Europaea

Professor Ed Ott has been elected a foreign member of the Academia Europaea for his outstanding achievements and international scholarship as a researcher. He is globally known for his pioneering contributions in nonlinear dynamics and chaos theory.

Ott is a University of Maryland Distinguished University Professor and holder of the Yuen Sang and Yu Yuen Kit So Endowed Professorship in nonlinear dynamics. He received the 2014 Julius Edgar Lilienfeld Prize of the American Physical Society, and in 2017, the Lewis Fry Richardson Medal of the European Geosciences Union. Also in 2017, he was selected for the Jürgen Moser Lecture, sponsored by the Society for Industrial and Applied Mathematics (SIAM).  

Ott is a Fellow of the Society for Industrial and Applied Mathematics, the American Physical Society and the Institute of Electrical and Electronics Engineers. He received his B.S. in Electrical Engineering at The Cooper Union and his M.S. and Ph.D. in Electrophysics from Polytechnic Institute, then enjoyed a postdoctoral fellowship at the Department of Applied Mathematics and Theoretical Physics of Cambridge University. Returning stateside, he joined the Electrical Engineering faculty at Cornell. He left Ithaca in 1979 to join the Department of Physics and Department of Electrical Engineering on this campus. He is a member of the Institute for Research in Electronics and Applied Physics (IREAP), and has held appointments at the Naval Research Lab and what is now the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara.

The Academia Europaea fosters excellence in scholarship in the humanities, law, social and hard sciences.  

Lila Snow, 1927 - 2020

Lila Snow, a noted local artist and television host, died on July 13. She was the wife of George Snow, a UMD professor of high energy physics from 1958 to 1992.

Lila, a native New Yorker, earned a degree in chemistry from Brooklyn College and studied art at the Corcoran School, American University and the University of Maryland.

In 1972, Lila and George co-taught the first Women’s Studies course on this campus. After her husband’s death in 2000, Lila established the George A. Snow Memorial Award, to acknowledge the paucity of women in the field of physics and encourage greater participation. The award has highlighted exceptional efforts within the department, including outreach, mentoring and innovation.

In 2016, Lila donated two original artworks, Particle Picture and Scienza, for display near the high energy group’s offices in the Physical Sciences Complex.

Other creations grace the permanent collections of Radford University, the American Association for the Advancement of Science, the American University Museum and the Philadelphia Museum of Judaica, as well as locations in Argentina, Italy and Japan.

She hosted The Art Scene on Montgomery Municipal Cable Television for two decades.

The sculpture Bradford near the UMD chemistry building, created by Lila Katzen, was donated to the UMD campus by George and Lila Snow.

In addition to art, Lila was interested in languages, and studied in Geneva, Paris, Rome, Bologna and Sendai. As a child, she was a double dutch jump rope champion; as an adult, a standup comedian at varied venues including physics conferences, nightclubs and the National Museum of Women in the Arts.  She penned a memoir, With A Name Like Tuchmacher..., and in 2003 received a Lifetime Achievement Award from Brooklyn College.

Lila is survived by Zachary Snow, of Rhinebeck, N.Y.; Andrew Snow of Chevy Chase, and Sara Snow of Vancouver, British Columbia; eight grandchildren; and three great-grandchildren.

Gifts in support of Washington artists can be made in her memory to the American University Museum. Please note “In memory of Lila Snow” in the correspondence.


Scientists See Train of Photons in a New Light

Flashlight beams don’t clash together like lightsabers because individual units of light—photons—generally don’t interact with each other. Two beams don’t even flicker when they cross paths.

But by using matter as an intermediary, scientists have unlocked a rich world of photon interactions. In these early days of exploring the resulting possibilities, researchers are tackling topics like producing indistinguishable single photons and investigating how even just three photons form into basic molecules of light. The ability to harness these exotic behaviors of light is expected to lead to advances in areas such as quantum computing and precision measurement.

In a paper recently published in Physical Review Research, Adjunct Associate Professor Alexey Gorshkov, Joint Quantum Institute (JQI) postdoctoral researcher Przemyslaw Bienias, and their colleagues describe an experiment that investigates how to extract a train of single photons from a laser packed with many photons.

In the experiment, the researchers examined how photons in a laser beam can interact through atomic intermediaries so that most photons are dissipated—scattered out of the beam—and only a single photon is transmitted at a time. They also developed an improved model that makes better predictions for more intense levels of light than previous research focused on (greater intensity is expected to be required for practical applications). The new results reveal details about the work to be done to conquer the complexities of interacting photons.A cloud of Rydberg atoms can scatter most light to whittle a laser down to train of individual photons. But photons can get re-absorbed within the larger control beam making things more complicated. (Credit: Przemyslaw Bienias, University of Maryland)A cloud of Rydberg atoms can scatter most light to whittle a laser down to train of individual photons. But photons can get re-absorbed within the larger control beam making things more complicated. (Credit: Przemyslaw Bienias, University of Maryland)

“Until recently, it was basically too difficult to study anything other than a few of these interacting photons because even when we have two or three things get extremely complicated,” says Gorshkov, whi is also a physicist at the National Institute of Standards and Technology and Fellow of the Joint Center for Quantum Information and Computer Science. “The hope with this experiment was that dissipation would somehow simplify the problem, and it sort of did.”

Trains, Blockades and Water Slides

To create the interactions, the researchers needed atoms that are sensitive to the electromagnetic influence of individual photons. Counterintuitively, the right tool for the job is a cloud of electrically neutral atoms. But not just any neutral atoms; these specific atoms—known as Rydberg atoms—have an electron with so much energy that it stays far from the center of the atom.

The atoms become photon intermediaries when these electrons are pushed to their extreme, remaining just barely tethered to the atom. With the lone, negatively charged electron so far out, the central electrons and protons are left contributing a counterbalancing positive charge. And when stretched out, these opposite charges make the atom sensitive to the influence of passing photons and other atoms. In the experiment, the interactions between these sensitive atoms and photons is tailored to turn a laser beam that is packed with photons into a well-spaced train.

The cloud of Rydberg atoms is kind of like a lifeguard at a water park. Instead of children rushing down a slide dangerously close together, only one is allowed to pass at a time. The lifeguard ensures the kids go down the slide as a steady, evenly spaced train and not in a crowded rush.

Unlike a lifeguard, the Rydberg atoms can’t keep the photons waiting in line. Instead they let one through and turn away the rest for a while. The interactions in the cloud of atoms form a blockade around each transmitted photon that scatters other photons aside, ensuring its solitary journey.

To achieve the effect, the researchers used Rydberg atoms and a pair of lasers to orchestrate a quantum mechanical balancing act. They selected the frequency of the first laser so that its photons would be absorbed by the atoms and scattered in a new direction. But this is the laser that is whittled down into the photon train, and they needed a way to let individual photons through.

That’s were the second laser comes in. It creates another possible photon absorption that quantum mechanically interferes with the first and allows a single photon to pass unabsorbed. When that single photon gets through, it disturbs the state of the nearby atoms, upsetting the delicate balance achieved with the two lasers and blocking the passage of any photons crowding too closely behind.

Ideally, if this process is efficient and the stream of photons is steady enough, it should produce a stream of individual photons each following just behind the blockade of the previous. But if the laser is not intense enough, it is like a slow day at the waterpark, when there is not always a kid eagerly awaiting their turn. In the new experiment, the researchers focused on what happens when they crowed many photons into the beam.

Model (Photon) Trains

Gorshkov and Bienias’s colleagues performed the experiment, and the team compared their results to two previous models of the blockade effect. Their measurements of the transmitted light matched the models when the number of photons was low, but as the researchers pushed the intensity to higher levels, the results and the models’ predictions started looking very different. It looked like something was building up over time and interfering with the predicted, desired formation of well-defined photon trains.

The team determined that the models failed to account for an important detail: the knock-on effects of the scattered photons. Just because those photons weren’t transmitted, doesn’t mean they could be ignored. The team suspected the models were being thrown off by some of the scattered light interacting with Rydberg atoms outside of the laser beam. These additional interactions would put the atoms into new states, which the scientists call pollutants, that would interfere with the efficient creation of a single photon train.

The researchers modified one of their models to capture the important effects of the pollutants without keeping track of every interaction in the larger cloud of atoms. While this simplified model is called a “toy model,” it is really a practical tool that will help researchers push the technique to greater heights in their larger effort to understand photon interactions. The model helped the researchers explain the behavior of the transmitted light that the older models failed to capture. It also provides a useful way to think about the physics that is preventing an ideal single photon train and might be useful in judging how effectively future experiments prevent the undesirable affects—perhaps by using cloud of atoms with different shapes.

“We are quite optimistic when it comes to removing the pollutants or trying to create less of them,” says Bienias. “It will be more experimentally challenging, but we believe it is possible.”

Original story by Bailey Bedford:

In addition to Bienias and Gorshkov, James Douglas, a Co-founder at MEETOPTICS; Asaf Paris-Mandoki, a physics researcher at Instituto de Física, Universidad Nacional Autónoma de México; JQI postdoctoral researcher Paraj Titum; Ivan Mirgorodskiy; Christoph Tresp, a research and development employee at TOPTICA Photonics; Emil Zeuthen, a physics professor at the Niels Bohr Institute; Michael J. Gullans, a former JQI postdoctoral researcher and current associate scholar at Princeton University; Marco Manzoni, a data scientist at Big Blue Analytics; Sebastian Hofferberth, a professor of physics at the University of Southern Denmark; and Darrick Chang, a professor at the Institut de Ciencies Fotoniques, were also co-authors of the paper.

Reference Publication
Research Contact
Przemyslaw Bienias: This email address is being protected from spambots. You need JavaScript enabled to view it.
(link sends e-mail)

Media Contact
Bailey Bedford: This email address is being protected from spambots. You need JavaScript enabled to view it.

(link sends e-mail)

Quantum Simulation Stars Light in the Role of Sound

Inside a material, such as an insulator, semiconductor or superconductor, a complex drama unfolds that determines the physical properties. Physicists work to observe these scenes and recreate the script that the actors—electrons, atoms and other particles—play out. It is no surprise that electrons are most frequently the stars in the stories behind electrical properties. But there is an important supporting actor that usually doesn’t get a fair share of the limelight.

This underrecognized actor in the electronic theater is sound, or more specifically the quantum mechanical excitations that carry sound and heat. Scientists treat these quantized vibrations as quantum mechanical particles called phonons(link is external). Similar to how photons are quantum particles of light, phonons are quantum particles of sound and other vibrations in a solid. Phonons are always pushing and pulling on electrons, atoms or molecules and producing new interactions between them.

The role that phonons play in the drama can be tricky for researchers to suss out. And sometimes when physicists identify an interesting story to study, they can’t easily find a material with all the requisite properties or of sufficient chemical purity.lCigar shaped clouds of atoms (pink) are levitated in a chamber where an experiment uses light to recreate behavior that normally is mediated by quantum particles of sound. (Credit: Yudan Guo, Stanford)Cigar shaped clouds of atoms (pink) are levitated in a chamber where an experiment uses light to recreate behavior that normally is mediated by quantum particles of sound. (Credit: Yudan Guo, Stanford)

To help overcome the challenges of working directly with phonons in physical materials, Professor Victor Galitski,  Joint Quantum Institute (JQI) postdoctoral researcher Colin Rylands and their colleagues have cast photons in the role of phonons in a classic story of phonon-driven physics. In a paper published recently in Physical Review Letters(link is external), the team proposes an experiment to demonstrate photons adequacy as an understudy and describes the setup to make the show work.

“The key idea came from an interdisciplinary collaboration that led to the realization that seemingly unrelated electron-phonon systems and neutral atoms coupled to light may share the exact same mathematical description,” says Galitski. “This new approach promises to deliver a treasure trove of exciting phenomena that can be transplanted from material physics to light-matter cavity systems and vice versa."

The Stage

Galitski and colleagues propose using a very carefully designed mirrored chamber—like coauthor Benjamin Lev has in his lab at Stanford University—as the stage where photons can take on the role of phonons. This type of chamber, called an optical cavity, is designed to hold light for a long time by bouncing it between the highly-reflective walls.

“We made cavities where if you stick your head in there—of course it's only a centimeter wide—you would see yourself 50,000 times,” says Lev. “Our mirrors are very highly polished and so the reflections don't rapidly decay away and get lost.”

In an optical cavity, the bouncing light can hold a cloud of atoms in a pattern that mimics the lattice of atoms in a solid. But if a cavity is too simple and can only contain a single light pattern—a mode—the lattice is frozen in place. The light has to be able to take on many modes to simulate the natural distortions of phonons in the material.

To create more dynamic stories with phonons, the team suggests using multimode confocal cavities. “Multimode confocal” basically means the chamber is shaped with unforgiving precision so that it can contain many distinct spatial distributions of light.

“If it were just a normal single-mode cavity—two curved mirrors spaced at some arbitrary distance from one another— it would only be a Gaussian shape that could bounce back and forth and would be kind of boring; your face would be really distorted,” says Lev. “But if you stick your face in our cavities, your face wouldn’t look too different—it looks a little different, but not too different. You can support most of the different shapes of the waveform of your face, and that will bounce back and forth.”

Mirrors with a green tint can be seen inside a small experimental cavity.Mirrors with a green tint can be seen inside a small experimental cavity.

View of the cavity mirrors that serve as a stage for quantum simulations where light takes on the role of sound. (Credit: LevLab, Stanford)

The variety of light distributions that these special cavities can harbor, along with the fact that the photons can interact with one atom and then get reflected back to a different atom, allows the researchers to create many different interactions in order to cast the light as phonons.

“It's that profile of light in the cavity which is playing the role of the phonons,” says Jonathan Keeling, a coauthor of the paper and a physicist at the University of St Andrews. “So the equivalent of the lattice distorting in one place is that this light is more intense in this place and less intense in another place.”

The Script

In the paper, the team proposes the first experiment to perform with these multimode confocal cavities—the first play to premier on the new stage. It’s a classic of condensed matter physics: the Peierls transition. The transition occurs in one-dimensional chains of particles with an attractive force between them. The attractive force leads the particles to pair up so that they form a density wave—two close particles and a space followed by two close particles and a space, on and on. Even a tiny pull between particles creates an instability that pulls them into pairs instead of distributing randomly.

In certain materials, the attractive pull from phonons is known to trigger a dramatic electrical effect through the Peierls transition. The creation of the density wave makes it harder for electrons to move through a material—resulting in a sudden transition from conductor to insulator.

“The Peierls transition is mathematically very similar to, but less well known than, superconductivity,” says Rylands. “And, like in superconducting systems, or many other systems that you would study in a solid-state lab, all these different phases of matter are driven by the interactions between phonons and the electrons.”

To recast the phonons as light the team has to also recast the electrons in the 1D material as cigar shaped clouds of atoms levitated in the chamber, as shown in the image above. But in this case, they don’t have a sudden cut off of an electrical current to conveniently signal that the transition occurred like in the traditional experiments with solids. Instead, they predicted what the light exiting the cavity should look like if the transition occurs.

Opening Night

The authors say that the proposed experiment will debut in cavities in Lev’s lab.

“It’s kind of nice when you have an experimentalist on a theory paper—you can hold the theorists’ feet to the fire and say, ‘Well, you know, that sounds great, but you can't actually do that,’” says Lev. “And here we made sure that you can do everything in there. So really, it's a quite literal roadmap to what we're going to do in the near future.”

If this experiment lines up with their predictions, it will give them confidence in the system’s ability to reveal new physics through other simulations.

There is competition for which shows will get the chance to take central stage, since there are many different scripts of physical situations that researchers can use the cavities to explore. The technique has promise for creating new phases of matter, investigating dynamic quantum mechanical situations, and understanding materials better. The cavities as stages for quantum simulations put researchers in the director’s chair for many quantum shows.

Original story by Bailey Bedford: 

A note from the researchers: The JQI and Stanford collaborators are especially grateful for support from the US Army Research Office, and discussions with Dr. Paul Baker at US-ARO, that made this work possible.

In addition to Galitski, Rylands, Lev and Keeling, Stanford graduate student Yudan Guo was also a co-author of the paper.

Research Contact
Colin Rylands: This email address is being protected from spambots. You need JavaScript enabled to view it.
(link sends e-mail)

Media Contact
Bailey Bedford: This email address is being protected from spambots. You need JavaScript enabled to view it.

(link sends e-mail)