Quantum Computing

Welcome, Prof. Josiah Sinclair!

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Josiah Sinclair

When he was younger, UW–Madison assistant professor of physics Josiah Sinclair wanted to be a scientist-inventor when he grew up. In high school, he would ask questions in biology and chemistry classes that his teachers said were really physics questions. So, when he began his undergrad at Calvin University, he majored in physics, believing that experimental physics would be at the intersection of his interests. In the end, it was quantum physics that really fascinated him, motivating him to complete a PhD in experimental quantum optics and atomic physics at the University of Toronto. He says, “The ethos of my PhD group was this idea that with modern technology, maybe we can invent an apparatus that can reproduce the essential elements of this or that classic thought experiment and learn something new.” After completing a postdoc at MIT, Sinclair joined the UW–Madison physics department as an assistant professor in August, where he will tinker in the lab as an experimental quantum physicist, and just maybe invent a new kind of neutral atom quantum computer.

Please give an overview of your research.

There’s a global race underway to build a quantum computer—a machine that operates according to the laws of quantum mechanics and uses an entirely different, more powerful kind of logic to solve certain problems exponentially faster than any classical computer can. Quantum computers won’t solve all problems, but there’s strong confidence they’ll solve some very important ones. Moreover, as we build them, we’re likely to discover new applications we can’t yet imagine.

The approach my group focuses on uses arrays of single neutral atoms as qubits. Right now, the central challenge in practical quantum computing is how to scale up quantum processors without compromising their quality. Today’s atom-array quantum computers are remarkable, hand-built systems that have reached hundreds or even thousands of qubits in recent years—a truly impressive feat and possible in part due to pioneering work done right here in Madison. However, as these systems grow larger, we’re hitting fundamental size limits that call for new strategies.

My lab is working to develop modular interconnects for neutral-atom quantum computers. Instead of trying to build a single massive machine, we aim to link multiple smaller systems together using single photons traveling through optical fibers. The challenge is that single photons are easily misplaced, so to make this work, we need to develop the most efficient atom–photon interfaces ever built—pushing the limits of our ability to control the interaction between one atom and one photon.

Once we get these quantum links working, we’ll have realized the essential building block for a truly scalable quantum computer and maybe someday the quantum internet. Beyond computing, these technologies could also enable new kinds of distributed quantum sensors, where multiple quantum systems work together to detect extremely faint signals spread across a large area, like photons arriving from distant planets.

What are the one or two main projects your new group will work on?

Our main focus will be to build two neutral atom quantum processors in adjacent rooms and link them together with an optical fiber. This project will teach us how to integrate highly efficient photonic interfaces—such as optical cavities—with atom arrays, and how to precisely control the interactions between atoms and photons. Step by step, we aim to demonstrate atom-photon entanglement and eventually send quantum information back and forth through the fiber.

We’re collaborating with a new company called CavilinQ, a Harvard spin-out supported by Argonne National Lab, to integrate a new cavity design with the geometry we want to explore for atom-photon coupling. Because we intend to iterate rapidly on the cavity design, our setup will be built on a precision translation stage, allowing us to easily slide the system in and out and swap out cavity components.

Another project in the lab will focus on developing a new kind of cold-atom quantum sensor. Most current sensors rely on magneto-optical traps, which require bulky electromagnets and impose constraints that limit performance. We plan to explore magnetic-field-free trapping techniques that could lead to simpler, more compact, and ultimately higher-performance quantum sensors.

What attracted you to Madison and the university?

Well, for me professionally, Madison’s a powerhouse in atomic physics and quantum computing. There are groups here that have been highly influential since the beginning in developing neutral atoms as a platform for quantum information science. So there’s a strong atomic physics community here that has incredible overlap with my research interests, and a thriving broader quantum information community as well. Some people work best in isolation, but that is not who I am, so the prospects of joining this vibrant collaborative environment was very appealing to me.

I also really enjoyed all my interactions with the members of the search committee and other faculty here both during my interview and subsequent visits. On the personal side, my wife’s family is all in the Chicago area, so the prospects of being so close to one side of the family were very appealing. We have a 18-month-old daughter, and when we visited, we just had such a positive impression of Madison as a place to have a family and to grow up.

What is your favorite element and/or elementary particle?

It’s rubidium. I worked with it in my PhD, I worked with it in my postdoc, and I will work with it again. It’s simple. It has one electron in the outer valence shell, which makes it easy to work with. It was one of the first atoms to be laser cooled and one of the first to be Bose condensed, but I think it still has some tricks for us up its sleeve. I believe the first quantum computers are going to be built out of rubidium atoms. Some people (and companies) think we will need a more complicated atom, like strontium or ytterbium, but I think we already have the atom we need—we just need to figure out how to make it work.

What hobbies and interests do you have?

In the last year: spending time with my eighteen-month-old daughter. It’s been a special time. I also enjoy photography. I do some photography of research labs, but mostly I do adventure photography. I don’t think of myself as a particularly talented photographer, my specialty is more being willing to lug a heavy camera up a mountain. I also really enjoy cycling, rock climbing, reading, and traveling.

 

 

Matt Otten earns Air Force Young Investigator Research Program award

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Matt Otten has won an Air Force Young Investigator Research Program (YIP) award, offered through the Air Force Office of Scientific Research.

The program intends to support early-career scientists and engineers who show exceptional ability and promise for conducting basic research. Nearly 40 awards were expected to be made in this cycle.

The three-year, $450,000 award will fund a postdoctoral fellow in Otten’s group, who will work on quantum characterization, verification, and validation (QCVV) of quantum computers. QCVV asks if a quantum computer is working and what the device’s limitations are, in an effort to engineer a better system in future iterations.

With any quantum computer, researchers input different tasks and calculations under different conditions, then receive back some classical data that describes the quantum state. Otten describes what happens between input and output as “a black box.”

“Our work is trying to open that black box and put in physics,” Otten says. “And we’re starting from a good place: we already have good models of what those qubits do and how they’re supposed to behave, and we can fit the parameters of the model to the observations of the data.”

Otten’s group will collaborate with experimentalists on their quantum computers. If the data fit the model, it suggests that the quantum computer is behaving as predicted and that the researchers understand the full process. But if the date do not — and given that a major impediment to quantum computing has been understanding and controlling errors, this scenario is more likely — then the researchers will need to determine why.

“That’s the goal of the research, to develop the techniques so that we can tie the errors that we see in the data to a physical source for that error, and then we can give feedback to the experimentalists,” Otten says. “And maybe they can tell me what went wrong without doing this complicated QCVV, but as we build bigger and bigger systems, this problem becomes harder to solve.”

U.S. Cyber Command visit highlights UW–Madison’s leadership in cyber research and education

a group of people walks through a room with equipment

UW–Madison plays a leading role as a research and education partner for national cybersecurity. It reinforced this commitment recently by welcoming to campus a delegation from the United States Cyber Command (USCYBERCOM), which is responsible for the Department of Defense’s cyberspace capabilities.

Read the full article at: https://news.wisc.edu/u-s-cyber-command-visit-highlights-uw-madisons-leadership-in-cyber-research-and-education/

Welcome, Prof. Britton Plourde!

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Britton Plourde (credit: Isabelle Delfosse, L&S)

Condensed matter experimentalist Britton Plourde received his bachelor’s in physics and music performance from the University of Michigan. He then went to grad school at UIUC, earning a PhD in physics and a master’s in music performance. He completed a postdoc at UC-Berkeley, then began as an assistant professor of physics at Syracuse University in 2005, moving up the ranks to full professor there. In Fall 2024, Plourde joined the UW–Madison physics department as a full professor. He is joining the department on a half-time appointment; for the other half, he will be working at Qolab, a quantum computing startup company based in Madison.

 Please give an overview of your research.

I work on superconducting quantum circuits. We make microfabricated superconducting circuits that have what are called Josephson tunnel junctions in them. And one of the biggest things we use these for is making qubits. We study all of the various physics related to how qubits work, what limits their performance, and ways to make them perform better so you could eventually build a practical, large-scale quantum computer. My research is similar to Robert McDermott’s and Roman Kuzmin’s.

What are the first one or two projects that you will have your group working on or continuing to work on when you arrive in Madison?

The company I’m working with, Qolab, is focused on building a quantum computer. My academic research lab at the university will be focused on fundamental physics related to operation of qubits, including the individual components of qubits like the Josephson junctions and to different processes that limit the performance of qubits. At the same time, the company is really focused on the technology of fabricating lots of qubits in a uniform, reproducible way and building them into a quantum computer.

In my group, a significant focus is going to be on understanding quasiparticles in superconducting qubits and how they impact the behavior of those qubits. Quasiparticles are electronic excitations above the superconducting ground state. The superconducting ground state is important because it doesn’t have any dissipation. But these quasiparticles are dissipative, and they can degrade the performance of a superconducting circuit. There are various things that can generate the quasiparticles, but one of them is radioactivity: background radiation from radioactive contaminants in the lab or from cosmic rays. My group is going to continue spending time on understanding the physics of those processes and coming up with ways to try to mitigate their effects to make qubits that are more immune to quasiparticles.

We’re also hoping to study quasiparticle physics in qubits for the completely opposite reason: instead of trying to mitigate the effects of quasiparticles to make better qubits, it’s to amplify the effects of quasiparticles to make better detectors, potentially to detect dark matter particles. Robert and I are co-principal investigators with some particle physics collaborators on two Department of Energy proposals for this work that we recently submitted. This work hasn’t been funded yet, but if it is, it is going to be a new and interesting research direction in both of our groups.

What attracted you to Madison and the university?

It’s a great department. I’ve known it for a long time because I collaborated with Robert almost as long as he’s been there. I’ve visited a lot over the years, and I like the area and the city. The university has made an impressive investment in quantum information science, and they’re a real leader in that area and have research strengths across multiple different qubit technologies, both experimentally and with a strong team of theorists working on different aspects of quantum information science and condensed matter. It’s really a powerhouse place, so I’m excited to join. University leadership has also been very supportive of the startup, they’re strongly encouraging of the entrepreneurial direction of faculty, and that’s not the case at a lot of other places.

What is your favorite element and/or elementary particle?

My favorite element has to be aluminum. That’s the superconductor we use the most. The same aluminum that you could use to wrap a hot dog at a baseball game to keep it warm, you can instead cool it down to below one degree Kelvin and it becomes a superconductor. And it makes great Josephson junctions for qubits.

What hobbies and interests do you have?

Well, I’m still a musician, I’m a flutist. I don’t really make money on it anymore, but I was a professional musician for a while. For the last three years of grad school, I had a job in a professional orchestra. I do still play occasionally, and I’ll have to see how much time I have when we get to Madison. My wife is a professional musician. She’s an oboist and she’ll be working part time in the School of Music developing a new monthly recital series.

Welcome, Professor Ben Woods!

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Ben Woods

Condensed matter theorist Ben Woods joined the department as an assistant professor this fall. Originally from a small town in North Dakota, Woods studied physics at the University of North Dakota and earned a PhD in physics from West Virginia University. He first came to UW–Madison for a postdoc with Mark Friesen in 2021, and now moves into his faculty role.

Please give an overview of your research.

I primarily work in two main areas of condensed matter theory and quantum information science. The first area is the theory of semiconductor quantum dots, with applications towards building and operating quantum computers based on spin qubits. Quantum dots can be thought of as artificial atoms in which electrons are trapped and manipulated within a semiconductor, such as silicon, by metallic gates that sit on top of the semiconductor. An electron in the quantum dot forms the basis for a type of qubit called a spin qubit, where the quantum information is stored in the spin of the electron. I investigate how we can build higher quality spin qubits. One aspect of this is analyzing and designing single and two qubit gates such that their efficiency and noise resiliency can be improved. Another aspect is studying the materials and design of quantum dot devices to optimize certain properties, such as how the qubits respond to an external magnetic field. I am also interested in quantum dot arrays as a platform for quantum simulation. Here the idea is to engineer the interactions between the quantum dots to emulate a quantum system of interest.

The other area I work in is semiconductor-superconductor heterostructures. Here, you’re trying to combine desirable properties of both types of materials to create interesting devices that would otherwise be impossible. I study semiconductor-superconductor heterostructures that can give rise to exotic particles known as Majorana zero modes, which form the basis for topological qubits. These qubits are immune to certain error sources that more conventional types of qubits are not. I am trying to understand the effects of disorder on these heterostructures and develop new schemes in which Majorana zero modes can be realized.

What are one or two of the main projects your group will work on first?

One initial project will focus on designing a new qubit architecture for quantum dot spin qubits. In the most conventional type of spin qubit, you have a single electron spin that is manipulated by jiggling it with an electric field back and forth within a single quantum dot. It turns out, however, that these qubits can be manipulated more efficiently if you can hop electrons between multiple quantum dots. Specifically, I’ve devised new schemes involving three dots in a triangular geometry in which single-qubit gates can be performed quite efficiently. These ideas work in principle, but now it’s a matter of quantitatively studying how noise resilient the scheme is and how finely tuned the system parameters need to be for things to go as planned.

A second initial project is more towards quantum simulation using quantum dot arrays. The project will focus on studying magnetism in quantum dot arrays. In other words, asking how the spins of the quantum dot electrons organize due to their mutual interaction. One interesting wrinkle in these quantum dot arrays based on silicon is that there is a valley degree of freedom in addition to the usual spin degree of freedom. The project involves understanding the effects on the magnetic ordering due to this additional valley degree of freedom. Specifically, I am interested in how fluctuations in the valley degree of freedom from one dot to the next can impact magnetic ordering.

What attracted you to Madison and the university?

There were two main reasons. First, my wife had gotten a residency as an anesthesiologist at the UW hospital. So that was an obvious motivation. Second, one of my grad school advisors knew Mark Eriksson and Mark Friesen and thought it’d be a natural fit for me to work with them as a postdoc. Since moving here, my family has enjoyed Madison, and I really like the physics department. The people are very friendly and collaborative. I am incredibly happy to be able to stay in Madison and at the UW physics department.

What is your favorite element and/ or elementary particle?

It has to be silicon, right? It’s the material I think about every day. And the world economy is largely based on stuff made with silicon. So that’s pretty cool?

What hobbies and interests do you have?

I like to play guitar, read, watch sports, and spend time with my family and friends. I have two kids, three years and six months old, who I like to spend most of my free time on.

Mark Eriksson named Steenbock Professor

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This story was originally published by the Office of the Vice Chancellor for Research

Mark Eriksson, professor of physics, and Mikhail Feldman, professor of mathematics, have been named recipients of UW–Madison Steenbock Professorships.

“This professorship is among the most prestigious and important professorships for researchers at the UW–Madison,” says Cynthia Czajkowski, interim vice chancellor for research. “This recognition is accompanied by discretionary funds to provide recipients the freedom to explore innovative research directions and to explore new approaches to their research areas.”

In the early 1980s, Evelyn Steenbock initiated a program to endow a series of professorships in the natural sciences in honor of her late husband, Harry Steenbock, emeritus professor of biochemistry.

Harry Steenbock (1886-1967) developed an inexpensive method of enriching foods with Vitamin D. His discovery led to the eradication of rickets, the bone-deforming deficiency disease, throughout most of the world. He is also renowned for his discovery of the conversion of carotenes to vitamin A.

Steenbock assigned his patents for advances in human and animal nutrition to the Wisconsin Alumni Research Foundation (WARF), and accumulated royalties from Steenbock’s patents supplied about half the funds for the Steenbock Memorial Library construction on campus. Steenbock Memorial Library is a primary resource library for the students, faculty and research staff at the UW­–Madison.

The Steenbock Professorship provides research funds to recipients annually for 10 years and honors those faculty who have made major contributions to the advancement of knowledge, primarily through their research endeavors at UW­–Madison, but also as a result of their teaching and service activities.

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Mark Eriksson

Eriksson, awarded the Steenbock Professorship in the Physical Sciences, was recently chair of the Department of Physics. He joined the UW–Madison physics faculty in 1999 and is a world-leading expert in the development of quantum information systems using solid-state quantum dot qubits.

As department chair, Eriksson promoted the Wisconsin Idea by supporting the department’s role in connecting with audiences all around the state of Wisconsin, including restarting The Wonders of Physics Traveling Show.

Eriksson received a bachelor’s degree in physics and mathematics from UW–Madison in 1992, received his PhD from Harvard University and was a postdoctoral member of technical staff at Bell Labs.

His research has focused on quantum computing, semiconductor quantum dots and nanoscience. He leads a team dedicated to developing spin qubits in gate-defined silicon quantum dots with the goal of enabling quantum computers, which manipulate information coherently, to be built using many of the materials and fabrication methods that are the foundation of modern, classical integrated circuits.

Eriksson is widely recognized for engaging collaborative partnerships with industry, government leaders and other university research institutions to tackle some of the greatest challenges in quantum information science and technology. Last year, the Eriksson group announced its partnership with Intel and HRL Laboratories as part of the LPS Qubit Collaboratory (LQC) national Quantum Information Science Research Center hosted at the Laboratory for Physical Sciences at the University of Maryland, College Park to collaborate on research in advanced computer technologies.

“I intend to use the award to explore new opportunities in silicon-based quantum computing, including new ideas for connecting qubits to each other across large distances, and the use of near-atomic-scale metamaterials to endow semiconductors with properties even better suited to quantum computing than those available today,” Eriksson says.