Connecting the Quantum Dots

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Category: Department News

Published: Wednesday, January 29 2025 01:40

Physics Ph.D. student Anantha Rao tests ways to build bigger and better quantum computers.

Anantha Rao grew up in Bengaluru, a city known as India’s tech hub due to its bustling startup culture and many international IT corporations. While many of Rao’s peers pursued engineering and related subjects, Rao’s love of science and knack for solving mathematical problems nudged him in a different direction.

“Everyone around me was an engineer or wanted to be one, and that is one thing I did not want to be,” Rao said. “I had this rebellious nature of going against the crowd, but I also wanted to solve fundamental problems in the basic sciences for the love of it—not for immediate applications.”

Rao discovered his calling after winning a high school physics competition. As a prize, he received a book written by Richard Feynman, a theoretical physicist who laid the groundwork for the field of quantum computing more than 40 years ago, and the field’s endless applications captivated Rao.

“Quantum computing has applications in studying how drug molecules bind to receptors or decrypting credit card transactions. You could study models of how the universe was created or see how the first molecule came into the picture,” Rao said. “Using ideas from quantum mechanics and computer science, you can also build better quantum computers, which is the problem that I’m looking at today.”

Now a Ph.D. student in the University of Maryland’s Department of Physics and Joint Center for Quantum Information and Computer Science (QuICS), Rao probes the fundamental physics that could power the next generation of quantum computers. He said he’s grateful for the chance to pursue that challenge in the “Capital of Quantum” at UMD.

“UMD is one of the top schools in the world for quantum information, especially theory,” Rao said. “Ten years ago, if someone told me that I'd be here now, I would feel like it is a dream.”

Tackling malaria with tech

Before moving to the United States, Rao was a full-time physics student and part-time entrepreneur in India. While Rao was enrolled in a combined bachelor’s and master’s program at the Indian Institute of Science Education and Research Pune, he cofounded a startup to develop diagnostic tools for diseases like malaria, a mosquito-borne infection that kills an estimated 608,000 people per year, according to the U.S. Centers for Disease Control and Prevention.

The software he developed, dubbed Deep Learning for Malaria Detection (DeleMa Detect), relied on artificial intelligence (AI) to search patients’ blood smear images for the signs and stages of malaria infection. This technology is packed into a small, portable device, reducing the need for lab tests that can be costly and inaccessible in many parts of the world.

Rao’s startup received a $50,000 grant and won top prize at the International Genetically Engineered Machine (iGEM) 2021 Startup Showcase. Rao has since moved on to other projects but said his early entrepreneurial experience taught him lessons about project leadership and collaboration that he applies to his research every day.

“I learned a lot about AI during my brief stint with entrepreneurship, and that’s something I've been working on lately—using AI to solve problems in physics,” Rao said. “My main motivation now is: What are the toughest problems out there and how can I solve them?Rao at TU Delft.

Since joining UMD’s physics Ph.D. program in 2023, he has been working to identify—and answer—those questions, one at a time.

The making of MAViS

One of Rao’s biggest ongoing projects is a collaboration between UMD, the National Institute of Standards and Technology and Delft University of Technology in the Netherlands. He has been leading the Modular Autonomous Virtualization System for Two-Dimensional Semiconductor Quantum Dot Arrays (MAViS) project, which aims to advance research that could lead to bigger and better quantum dot-based quantum computers.

Central to this concept are quantum dots, tiny semiconductor particles that serve as the building blocks of some quantum computers. These quantum computers operate at temperatures close to absolute zero, or −273.15 degrees Celsius—conditions that prompt the chips to engage in quantum mechanical behavior.

“The chips in your phone and chips in your laptop are made up of semiconductors, and similarly, we have quantum computers made out of semiconductors, except they operate at the coldest temperatures in the universe,” Rao explained. “The problem is you can't control them very well and you have a lot of unwanted interactions coming in.

To control each quantum dot, voltages must be applied to electrodes in their vicinity. Isolating this task can be tricky, though, because quantum dots are spaced just a few nanometers apart.

“What MAViS offers is a way to independently control each quantum dot in a very scalable and efficient way. This is a process called virtualization,” Rao explained. “Most importantly, it’s completely automatic. You press a button and MAViS solves a lot of equations faster than any human.”

By finding ways to offset unwanted interactions, which can introduce errors, researchers can make quantum computers run more efficiently and accurately. MAViS also uses “a little bit of AI” to enable corrections in real-time, Rao said.

Rao and his collaborators have seen encouraging results after testing MAViS on some of the world’s largest quantum dot devices in the Netherlands. MAViS successfully enabled researchers to operate and more efficiently control quantum dots, which in turn helps them control qubits—the fundamental building blocks of quantum computers.

Rao explained that one of the benefits of MAViS is that it works quickly and could free up time for researchers to focus on deeper tasks.

“We were able to do a task in about four hours that would have taken a month or two months of human effort,” Rao said. “Without MAViS, a lot of people with doctorate degrees would have needed to stare at computer screens and analyze complicated images to solve this problem. Now, researchers can automatically ‘virtualize’ their quantum dots and perform interesting experiments.”

Aside from his research with MAViS, Rao said his research on semiconductor qubits has also revealed some unusual physics, including elusive crystals made entirely of electrons.

“Another question in my research is: If you have these semiconductor quantum dots or quantum computers, what is some interesting physics that one could study in one dimension or two dimensions?” Rao said. “We've found evidence that exotic phases of matter—something called Wigner crystals—could be found in these devices.”

Giving back

As Rao dives deeper into quantum physics, he continually seeks ways to share his knowledge. MAViS and many of Rao’s past research projects involve open-source code so that the community at large can benefit.

“Since undergrad, I’ve wanted to give back to the community as I’ve learned things, and one way is through open-source projects and mentoring other students,” said Rao, who also worked as a teaching assistant and served on graduate student committees at UMD. “We hope to eventually make MAViS open source so that people anywhere in the world can build better, scalable quantum-dot quantum computers.”

After Rao graduates, he hopes to find a job that will enable him to keep tackling the big questions in quantum physics, whether that’s in academia or private industry.

“My pursuit is the best research and the best science that I can do today, and I believe that approach will give me the right opportunity in an academic lab or industry lab,” Rao said. “There are a lot of problems to solve in quantum, and I’m working toward solving them one at a time.”

Written by Emily Nunez; published March, 2025

Zohreh Davoudi Awarded Presidential Early Career Award for Scientists and Engineers

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Category: Department News

Published: Thursday, January 16 2025 00:01

Zohreh Davoudi, an associate professor of physics at the University of Maryland and Maryland Center for Fundamental Physics, received the Presidential Early Career Award for Scientists and Engineers. The award, which was established in 1996 to recognize young professionals who have demonstrated exceptional potential for leadership in their fields, is the highest honor the U.S. government bestows on early-career scientists and engineers.Zohreh Davoudi

Davoudi, who is also a Fellow of the Joint Center for Quantum Information and Computer Science and the Associate Director for Education at the NSF Quantum Leap Challenge Institute for Robust Quantum Simulation, is one of 398 scientists and engineers nationwide to be acknowledged by President Biden.

“I am truly honored by this recognition,” Davoudi says. “This award signifies that the President and the U.S. government appreciate the important role scientists and engineers play in advancing society. I am excited to continue exploring the frontiers of nuclear physics and quantum information science using advanced classical- and quantum-computational methods and to continue building a community of amazing junior and senior collaborators who share the same or similar goals.”

Davoudi’s research focuses on strongly interacting quantum systems and investigates how elementary particles, like quarks and gluons, come together and form the matter that makes up our world. Her work to understand the foundations of matter includes developing theoretical frameworks and applying cutting-edge tools, like quantum simulations, to studying problems in nuclear and high-energy physics. Ultimately, she hopes to describe the evolution of mater into steady states that occurred in the early universe and that happens at a smaller scale in the aftermath of high-energy particle collisions, like those in experiments at the Large Hadron Collider.

Davoudi has also been acknowledged by other awards, including a Simons Emmy Noether Faculty Research Fellowship, an Alfred P. Sloan Fellowship, a Department of Energy's Early Career Award and a Kenneth Wilson Award in Lattice Gauge Theory.

“Zohreh is an exceptionally agile physicist and an expert in nuclear theory,” says Steve Rolston, a professor and chair of the Department of Physics at the University of Maryland. “She has embraced the new world of quantum computing and is now a leader in figuring out how to use quantum computation to solve challenging nuclear and high-energy physics problems.”

Original story by Bailey Bedford

Next Gen Retroreflectors Launch to the Moon

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Category: Department News

Published: Wednesday, January 15 2025 14:02

On January 15, 2025, a precision prism reflector devised by UMD physicists once again headed to the moon, continuing a tradition begun in 1969, when the Apollo 11 crew positioned still-functioning Lunar Laser Ranging Retroreflectors (LLRR). The new lunar lander reached the Moon on March 2, 2025, and the next day successfully communicated with French Lunar Laser Ranging Observatory at Grasse, France. A single 10 cm diameter corner cube retroreflector. Credit: Doug Currie

One of the physicists responsible for the original retroreflectors, Doug Currie, is the PI for the current version, Next Generation Lunar Retroreflectors (NGLR).  Using intense, brief lasers pulses, scientists on Earth will reflect light off the instrument, allowing measurements of the earth-moon distance to within 1 mm of accuracy. Such precision will allow better understanding of the moon’s liquid corA SpaceX Falcon 9 rocket carrying Firefly Aerospace’s Blue Ghost Mission One lander on January 15, 2024. Credit: NASA/Frank Michauxe and of general relativity.

Currie’s proposal was accepted as part of NASA’s Commercial Lunar Payload Services (CLPS) project, utilizing partnerships with private industry to facilitate space launches.  Blue Ghost Mission 1 by Firefly Aerospace launched at 1:11 a.m. on January 15 aboard a SpaceX Falcon 9 rocket from NASA’ Kennedy Space Center in Florida, with NGLR-1 and nine other experiments. 

Currie’s storied career and the preparation for the NGLR were detailed in the September 2024 issue of Terp magazine.

He was a UMD Assistant Professor, working with LLRR PI Professor Carroll Alley, at the time of the historic first venture of humans to the moon. In 2019, he was interviewed on the 50^th anniversary of Apollo 11, and was also selected for further work on retroreflectors. While the Apollo 11 retroreflectors were an array of small precision mirrors, the NGLR-1 is is a single 10 cm diameter corner cube retroreflector.

In addition to Currie, the UMD team on NGLR-1 included co-PI Drew Baden, deputy PI Dennis Wellnitz, Project Manager Ruth Chiang Carter and researchers Martin Peckerar, Chensheng Wu and Laila Wise.

Liftoff occurs at 43:01.

Twisted Light Gives Electrons a Spinning Kick

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Category: Research News

Published: Saturday, November 30 2024 01:00

It’s hard to tell when you’re catching some rays at the beach, but light packs a punch. Not only does a beam of light carry energy, it can also carry momentum. This includes linear momentum, which is what makes a speeding train hard to stop, and orbital angular momentum, which is what the earth carries as it revolves around the sun.

In a new paper, scientists seeking better methods for controlling the quantum interactions between light and matter demonstrated a novel way to use light to give electrons a spinning kick. They reported the results of their experiment, which shows that a light beam can reliably transfer orbital angular momentum to itinerant electrons in graphene, on Nov. 26, 2024, in the journal Nature Photonics.

Having tight control over the way that light and matter interact is an essential requirement for applications like quantum computing or quantum sensing. In particular, scientists have been interested in coaxing electrons to respond to some of the more exotic shapes that light beams can assume. For example, light carrying orbital angular momentum swirls around its axis as it travels. When viewed head-on, a light beam with orbital angular momentum contains a dark spot in the middle, a vortex opened up by the beam’s corkscrew character.In a new experiment, light beams carrying orbital angular momentum caused electrons in graphene to gain (blue beam) and lose (red beam) angular momentum, transporting them across the sample and generating a current that researchers measured. (Credit: Mahmoud Jalali Mehrabad/JQI)

“The interaction of light that has orbital angular momentum with matter has been thought about since the 90s or so,” says Deric Session, a postdoctoral researcher at JQI and the University of Maryland (UMD) who is the lead author of the new paper. “But there have been very few experiments actually demonstrating the transfer.”

Part of the challenge has been a size mismatch. In order for electrons to feel a tug from a light beam carrying momentum, they have to experience the way that the beam changes as it passes by. In many cases, the length over which a light beam changes dwarfs the size of the matter that researchers are interested in manipulating, making it especially challenging to pick out electrons as targets.

For instance, atoms and their orbiting electrons—mainstays of quantum physics experiments and favorite targets for precise manipulation—are roughly 1,000 times smaller than the light beams that researchers use to interact with them. Light travels as repeating waves of electric and magnetic fields, and the length that a light beam travels before it repeats is called the wavelength. In addition to being an important characteristic size, the wavelength of light also determines the amount of energy carried by individual particles of light called photons. Only photons that carry particular amounts of energy can interact with atoms, and those photons tend to have wavelengths much bigger than the atoms themselves. So while atoms as a whole will happily absorb energy and momentum from these photons, the wavelength is too big for the internal pieces of the atom—the nucleus and the electrons—to notice any relative difference. This makes it very difficult to transfer orbital angular momentum solely to an atom’s electrons.

One way to overcome this difficulty is to shrink the wavelength of light. But that increases the energy carried by each photon, ruling out atoms as reliable targets. In the new experiment, the researchers, who included JQI Fellows Mohammad Hafezi and Nathan Schine, JQI Co-Director Jay Sau and JQI Adjunct Fellow Glenn Solomon, pursued an alternate approach: Instead of shrinking the wavelength of the light, they puffed up electrons to make them occupy more space.

Electrons bound to the nucleus of an atom can only roam so far before they are liberated from the atom and useless for experiments. But in conductive materials, electrons have more latitude to travel far and wide while remaining under control. The researchers turned to graphene, a flat material that is one of the best known electrical conductors, in search of a way to make electrons take up more space.

By cooling a sample of graphene down to just 4 degrees above absolute zero and subjecting it to a strong magnetic field, electrons that are ordinarily free to move around become trapped in loops called cyclotron orbits. As the field gets stronger, the orbits become tighter and tighter until many circulating electrons are packed in so tightly that no more can fit. Although the orbits are tight, they are still much larger than the electron orbitals in atoms—the perfect recipe for getting them to notice light carrying orbital angular momentum.

The researchers used a sample of graphene wired up with electrodes for their experiments. One electrode was in the middle of the sample, and another made a ring around the outer edges. Earlier theoretical work, developed in 2021 by former JQI and UMD graduate student Bin Cao and three other authors of the new paper, suggested that electrons circulating in such a sample could gain angular momentum in chunks from incoming light, increase the size of their orbits and eventually get absorbed by the electrodes.

“The idea is that you can change the size of the cyclotron orbits by adding or subtracting orbital angular momentum from the electrons, thus effectively moving them across the sample and creating a current,” Session says.

In the new paper, the research team reported observing a robust current that survived under a wide range of experimental conditions. They hit their graphene sample with light carrying orbital angular momentum that circulated clockwise and observed the current flowing in one direction. Then they hit it with light carrying counterclockwise orbital angular momentum and found that the direction of the current flipped. They flipped the direction of the applied magnetic field and observed the current flip directions, too—an expected finding since changing the magnetic field direction also swaps the direction electrons flow in their cyclotron orbits. They changed the voltage across the inner and outer electrodes and continued to see the same difference between currents generated by clockwise and counterclockwise vortex light. They also tested sending circularly polarized light, which carries an intrinsic angular momentum, at the sample, and they found that it barely generated any current. In all cases, the signal was clear: The current only appeared in the presence of light carrying orbital angular momentum, and the direction of the current was correlated with whether the light carried momentum that spun clockwise or counterclockwise.

The result was the culmination of several years of work, which included some false starts with sample fabrication and difficulties collecting enough good data from the experiment.

“I spent over a year just trying to make graphene samples with this kind of geometry,” Session says. Ultimately, Session and the team reached out to a group they had worked with before, led by Roman Sordan, a physicist at the Polytechnic University of Milan in Italy and an expert at preparing graphene samples. “They were able to come through and make the samples that we used,” says Session.

Once they had samples that worked well, they still had trouble aligning their twisted light with the sample to observe the current.

“The signal we were looking at was not quite consistent,” says Mahmoud Jalali Mehrabad, a postdoctoral researcher at JQI and UMD and a co-author of the paper. “Then one day, with Deric, we started to do this spatial sweep. And we kind of mapped the sample with really high accuracy. Once we did that—once we nailed down the very peak, optimized position for the beam—everything started to make sense.” Within a week or so, they had collected all the data they needed and could pick out all the signals of the current’s dependence on the orbital angular momentum of the beam.

Mehrabad says that, in addition to demonstrating a new method for controlling matter with light, the technique might also enable fundamentally new measurements of electrons in quantum materials. Specially prepared light beams, combined with interference measurements, could be used as a microscope that can image the spatial extent of electrons—a direct measurement of the quantum nature of electrons in a material.

“Being able to measure these spatial degrees of freedom of free electrons is an important part of measuring the coherence properties of electrons in a controllable manner—and manipulating them,” Mehrabad says. “Not only do you detect, but you also control. That’s like the holy grail of all this.”

Original story: https://jqi.umd.edu/news/twisted-light-gives-electrons-spinning-kick

In addition to Session, Hafezi, Schine, Sau, Solomon, Cao, Sordan and Mehrabad, the paper had several other authors: Nikil Paithankar, a graduate student at the Polytechnic University of Milan in Italy; Tobias Grass, a former JQI postdoctoral researcher who is now a research fellow at the Donostia International Physics Center in Donostia, Spain; Christian Eckhardt, a graduate student at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany; Daniel Gustavo Suárez Forero, a former JQI postdoctoral researcher who will be starting as an assistant professor of physics at the University of Maryland, Baltimore County in 2025; Kevin Li, a former JQI and UMD undergraduate student; Mohammad Alam, a former JQI and UMD undergraduate student who now works at IonQ; and Kenji Watanabe and Takashi Taniguchi, both researchers at the National Institute for Materials Science in Tsukuba, Japan.

This work was supported by ONR N00014-20-1-2325, AFOSR FA95502010223, ARO W911NF1920181, MURI FA9550-19-1-0399, FA9550-22-1-0339, NSF IMOD DMR-2019444, ARL W911NF1920181, Simons and Minta Martin foundations, and EU Horizon 2020 project Graphene Flagship Core 3 (grant agreement ID 881603). Tobias Grass acknowledges funding by BBVA Foundation (Beca Leonardo a Investigadores en Fisica 2023) and Gipuzkoa Provincial Council (QUAN-000021-01).