Alex Levchenko, Mark Rzchowski elected Fellows of the American Physical Society

images shows two profile pictures, Alex Levchenko on the left and Mark Rzchowski on the right.

Congratulations to Profs. Alex Levchenko and Mark Rzchowski, who were elected 2022 Fellows of the American Physical Society!

Levchenko was elected for “broad contributions to the theory of quantum transport in mesoscopic, topological, and superconducting systems.” He was nominated by the Division of Condensed Matter Physics.

Rzchowski was elected for “pioneering discoveries and understanding of physical principles governing correlated complex materials and interfaces, including superconductors, correlated oxide systems multiferroic systems, and spin currents in noncollinear antiferromagnets.” He was nominated by the Division of Materials Physics.

APS Fellowship is a distinct honor signifying recognition by one’s professional peers for outstanding contributions to physics. Each year, no more than one half of one percent of the Society’s membership is recognized by this honor.

See the full list of 2022 honorees at the APS Fellows archive.

Margaret Fortman awarded Google quantum computing fellowship

This post was adapted from a story posted by the UW–Madison Graduate School

Two UW–Madison graduate students, including physics grad student Margaret Fortman, have been awarded 2022 Google Fellowships to pursue cutting-edge research. Fortman received the 2022 Google Fellowship in Quantum Computing, one of only four awarded.

profile picture of Margaret Fortman
Margaret Fortman

Google created the PhD Fellowship Program to recognize outstanding graduate students doing exceptional and innovative research in areas relevant to computer science and related fields. The fellowship attracts highly competitive applicants from around the world.

“These awards have been presented to exemplary PhD students in computer science and related fields,” Google said in its announcement. “We have given these students unique fellowships to acknowledge their contributions to their areas of specialty and provide funding for their education and research. We look forward to working closely with them as they continue to become leaders in their respective fields.”

The program begins in July when students are connected to a mentor from Google Research. The fellowship covers full tuition, fees, and a stipend for the academic year. Fellows are also encouraged to attend Google’s annual Global Fellowship Summit in the summer.

Fortman works to diagnose noise interference in quantum bits

Fortman, whose PhD research in Victor Brar’s group specializes in quantum computing, will use the fellowship support to develop a diagnostic tool to probe the source of noise in superconducting quantum bits, or qubits.

Quantum computing has the potential to solve problems that are difficult for standard computers, Fortman said, but the field has challenges to solve first.

“The leading candidate we have for making a quantum computer right now is superconducting qubits,” Fortman said. “But those are currently facing unavoidable noise that we get in those devices, which can actually come from the qubit material itself.”

Fortman works with a low-temperature ultra-high vacuum scanning tunneling microscope on the UW–Madison campus to develop a microscopic understanding of the origins of noise in qubits. She fabricates superconductors to examine under the microscope to identify the source of the noise, and hopefully be able to develop a solution for that interference.

In her time as a graduate student at UW–Madison, Fortman said she has enjoyed collaborating with colleagues in her lab and across campus.

“It’s pretty cool to be somewhere where world-renowned research is happening and to be involved with that,” she said. “My PI and I work in collaborations with other PIs at the university and they’re all doing very important research, and so it’s really cool to be a part of that.”

Fortman is excited to have a mentor at Google through the PhD Fellowship, having been paired with someone who has a similar disciplinary background and who is a research scientist with Google Quantum AI.

“He can be a resource in debugging some parts of my project, as well as general mentorship and advice on being a PhD student, and advice for future career goals,” Fortman said.

The second UW–Madison student who earned this honor is computer sciences PhD student Shashank Rajput, who received the 2022 Google Fellowship in Machine Learning.

Cross-institutional collaboration leads to new control over quantum dot qubits

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This story was originally published by the Chicago Quantum Exchange

Qubits are the building blocks of quantum computers, which have the potential to revolutionize many fields of research by solving problems that classical computers can’t.

But creating qubits that have the perfect quality necessary for quantum computing can be challenging.

Researchers at the University of Wisconsin–Madison, HRL Laboratories LLC, and University of New South Wales (UNSW) collaborated on a project to better control silicon quantum dot qubits, allowing for higher-quality fabrication and use in wider applications.

All three institutions are affiliated with the Chicago Quantum Exchange. The work was published in Physical Review Letters, and the lead author, J. P. Dodson, has recently transitioned from UW–Madison to HRL.

“Consistency is the thing we’re after here,” says Mark Friesen, Distinguished Scientist of Physics at UW–Madison and author on the paper.  “Our claim is that there is actually hope to create a very uniform array of dots that can be used as qubits.”

Sensitive quantum states

While classical computer bits use electric circuits to represent two possible values (0 and 1), qubits use two quantum states to represent 0 and 1, which allows them to take advantage of quantum phenomena like superposition to do powerful calculations.

Qubits can be constructed in different ways. One way to build a qubit is by fabricating a quantum dot, or a very, very small cage for electrons, formed within a silicon crystal. Unlike qubits made of single atoms, which are all naturally identical, quantum dot qubits are man-made—allowing researchers to customize them to different applications.

But one common wrench in the metaphorical gears of these silicon qubits is competition between different kinds of quantum states. Most qubits use “spin states” to represent 0 and 1, which rely on a uniquely quantum property called spin. But if the qubit has other kinds of quantum states with similar energies, those other states can interfere, making it difficult for scientists to effectively use the qubit.

In silicon quantum dots, the states that most often compete with the ones needed for computing are “valley states,” named for their locations on an energy graph—they exist in the “valleys” of the graph.

To have the most effective quantum dot qubit, the valley states of the dot must be controlled such that they do not interfere with the quantum information-carrying spin states. But the valley states are extremely sensitive; the quantum dots sit on a flat surface, and if there is even one extra atom on the surface underneath the quantum dot, the energies of the valley states change.

The study’s authors say these kinds of single-atom defects are pretty much “unavoidable,” so they found a way to control the valley states even in the presence of defects. By manipulating the voltage across the dot, the researchers found they could physically move the dot around the surface it sits on.

“The gate voltages allow you to move the dot across the interface it sits on by a few nanometers, and by doing that, you change its position relative to atomic-scale features,” says Mark Eriksson, John Bardeen Professor and chair of the UW–Madison physics department, who worked on the project. “That changes the energies of valley states in a controllable way.

“The take home message of this paper,” he says, “is that the energies of the valley states are not determined forever once you make a quantum dot. We can tune them, and that allows us to make better qubits that are going to make for better quantum computers.”

Building on academic and industry expertise

The host materials for the quantum dots are “grown” with precise layer composition. The process is extremely technical, and Friesen notes that Lisa Edge at HRL Laboratories is a world expert.

“It requires many decades of knowledge to be able to grow these devices properly,” says Friesen. “We have several years of collaborating with HRL, and they’re very good at making really high-quality materials available to us.”

The work also benefitted from the knowledge of Susan Coppersmith, a theorist previously at UW–Madison who moved to UNSW in 2018. Eriksson says the collaborative nature of the research was crucial to its success.

“This work, which gives us a lot of new knowledge about how to precisely control these qubits, could not have been done without our partners at HRL and UNSW,” says Eriksson. “There’s a strong sense of community in quantum science and technology, and that is really pushing the field forward.”

Victor Brar awarded prestigious Sloan Fellowship

University of Wisconsin–Madison physics professor Victor Brar has been named a 2021 Sloan Research Fellow, a competitive award given to researchers in the early stages of their careers.

Victor Brar

“A Sloan Research Fellow is a rising star, plain and simple,” says Adam F. Falk, president of the Alfred P. Sloan Foundation. “To receive a Fellowship is to be told by the scientific community that your achievements as a young scholar are already driving the research frontier.”

Brar’s research focuses on developing new microscopy techniques to look at quantum systems in ways that current microscopes cannot. Applying these techniques to study defects in materials — where a perfect crystal lattice is disrupted by one or more anomalous atoms — could lead to improvements in quantum computer performance or the discovery of new Physics.

“Everyone in the world is trying to make a quantum computer, but we don’t really have good diagnostics for what all the quantum systems are inside of a material,” Brar says. “One goal with this microscope is to figure out what’s in a material that could interfere with a quantum computer.”

Additionally, Brar hopes that by applying this technique to complex materials, new particles may be identified and studied. For example, many particle physics discoveries, such as the Higgs boson and the positron, have been first theorized based on materials science research and repurposed into high energy physics experiments.

“At CERN, for example, they try to get to higher and higher energies to see particles, and at some point CERN just can’t get high enough,” Brar explains. “But in a material, you can get analogous particles for what CERN scientists are looking for but at much lower energies. There are particles that we’ve never seen outside of a material, but we can see them in a material, and those are the kinds of things that we’d ideally like to study.”

Images of quantum defects embedded in the atomic lattice of tungsten diselenide (credit: Victor Brar)

The technique that Brar is developing combines optical and electron microscopy, two methods he worked on as a graduate student and post-doc. By bringing them together now, he hopes that his unique method will bring significant advances to his field — and that the Sloan Fellowship indicates that other scientists agree.

“The Sloan award has a history behind it, and they have a track record of funding good science,” Brar says. “So, it means a lot to be recognized by Sloan and I hope it will help when we start to try to make our case for why this method is important.”

The Sloan Research Fellowship is open to early-career scientists in one of eight fields, including physics. More than 1000 researchers are nominated each year for 128 fellowship slots. Winners receive a two-year, $75,000 fellowship which can be spent to advance the fellow’s research.

“Prof. Victor Brar winning the Sloan Foundation Fellowship is a very welcome recognition,” says Sridhara Dasu, chair of the UW–Madison physics department. “For decades now, the Sloan Fellowship is a highly sought-after honor amongst young scientists, and it is wonderful to note that our enthusiasm and confidence in Prof. Brar’s research prowess is recognized by an international panel selecting the Sloan Fellows.”