Research, teaching and outreach in Physics at UW–Madison
A better understanding of coral skeleton growth suggests ways to restore reefs
Coral reefs are vibrant communities that host a quarter of all species in the ocean and are indirectly crucial to the survival of the rest. But they are slowly dying — some estimates say 30 to 50 percent of reefs have been lost — due to climate change.
In a new study, University of Wisconsin–Madison physicists observed reef-forming corals at the nanoscale and identified how they create their skeletons. The results provide an explanation for how corals are resistant to acidifying oceans caused by rising carbon dioxide levels and suggest that controlling water temperature, not acidity, is crucial to mitigating loss and restoring reefs.
“Coral reefs are currently threatened by climate change. It’s not in the future, it’s in the present,” says Pupa Gilbert, a physics professor at UW–Madison and senior author of the study. “How corals deposit their skeletons is fundamentally important to assess and help their survival.”
Quantum technology experts from around the country will convene virtually on November 11-13 to forge new partnerships amid an exciting year for quantum research.
The third annual Chicago Quantum Summit, hosted by the Chicago Quantum Exchange, will bring together university, government, and industry leaders in the emerging field of quantum information science. The Chicago Quantum Exchange, headquartered at the University of Chicago’s Pritzker School of Molecular Engineering, is a leading national hub for the science and engineering of quantum information and for training tomorrow’s quantum workforce.
This year, the three-day virtual Summit will include presentations and discussions that focus on building collaborations between large-scale quantum research centers, companies, and innovators; fostering a quantum economic ecosystem and growing the quantum startup community; and developing a quantum-ready workforce. It will also include a public event on Nov. 12, featuring a presentation by Scott Aaronson, the David J. Bruton Centennial Professor of Computer Science at The University of Texas at Austin; and a fireside chat with Aaronson and David Awschalom, the director of the Chicago Quantum Exchange.
“The Chicago Quantum Summit will assemble leaders from across the community who are accelerating the development of quantum science and technology,” said Awschalom, who is also the Liew Family Professor in Spintronics and Quantum Information at the UChicago’s Pritzker School of Molecular Engineering and the director of Q-NEXT, a DOE quantum information science center led by Argonne National Laboratory. “This virtual event provides an opportunity to hear perspectives from the broader quantum community, to foster collaboration across large-scale initiatives, to help nurture tomorrow’s quantum engineers, and to develop the quantum economy.”
Speakers include Penny Pritzker, founder and chairman of PSP Partners and former U.S. Secretary of Commerce; Jim Clarke, director of quantum hardware at Intel; and Robert Zimmer, president of the University of Chicago, among others. The summit will also include presentations from leaders of newly announced Department of Energy and National Science Foundation-funded federal centers.
Three of these eight national centers are headquartered in Illinois: Q-NEXT, led by Argonne National Laboratory; the Superconducting Quantum Materials and Systems Center, led by Fermilab; and the Quantum Leap Challenge Institute for Hybrid Quantum Architectures and Networks, which is headquartered at the University of Illinois at Urbana-Champaign.
The recent investments in quantum science by the federal government and commitments by leading technology companies support the emerging quantum ecosystem and the development and translation of new technologies. The Summit session on Nov. 13 will focus on the economic impact of quantum science and technology, opportunities to hear from the investor community, and insights into cultivating quantum startups. Penny Pritzker, who also co-chairs P33, a private sector-led nonprofit dedicated to developing the Chicago region into a leading global tech and innovation hub, will give that day’s opening keynote. A panel discussion on advancing quantum startups will include speakers Christopher Monroe, co-founder and Chief Scientist, IonQ; Chris Savoie, founder and CEO, Zapata Computing; and Jennifer Elliott, co-founder and Vice President of Business Development, QEYnet.
“Quantum science has made significant progress in recent years and there is little doubt now that quantum computers will yield transformative products,” said Monroe. “We’re seeing more and more investment and companies getting into the quantum field, but to truly support early stage quantum companies, we need greater government leadership, additional investment and a supportive ecosystem in which to grow.”
This event is open to quantum-interested leaders, researchers, and trainees across industry, universities, government, and national laboratories. Learn more about the speakers, view the agenda, and register for the live sessions on the 2020 Chicago Quantum Summit event website.
Image credit: Peter Allen
How do astronomers test-drive a telescope?
Graduate student Leslie Taylor helped fine-tune a high-energy gamma-ray telescope this summer. Detecting the Crab Nebula was the “gold standard” for success.
Surprising communication between atoms could improve quantum computing
A group of University of Wisconsin–Madison physicists has identified conditions under which relatively distant atoms communicate with each other in ways that had previously only been seen in atoms closer together — a development that could have applications to quantum computing.
The physicists’ findings, published Oct. 14 in the journal Physical Review A, open up new prospects for generating entangled atoms, the term given to atoms that share information at large distances, which are important for quantum communications and the development of quantum computers.
“Building a quantum computer is very tough, so one approach is that you build smaller modules that can talk to each other,” says Deniz Yavuz, a UW–Madison physics professor and senior author of the study. “This effect we’re seeing could be used to increase the communication between these modules.”
The scenario at hand depends on the interplay between light and the electrons that orbit atoms. An electron that has been hit with a photon of light can be excited to a higher energy state. But electrons loathe excess energy, so they quickly shed it by emitting a photon in a process known as decay. The photons atoms release have less energy than the ones that boosted the electron up — the same phenomenon that causes some chemicals to fluoresce, or some jellyfish to have a green-glowing ring.
“Now, the problem gets very interesting if you have more than one atom,” says Yavuz. “The presence of other atoms modifies the decay of each atom; they talk to each other.”
Chuanhong (Vincent) Liu named to Fall 2020 cohort of the Quantum Information Science and Engineering Network (QISE-NET)
Graduate student Chuanhong (Vincent) Liu (McDermott Group) has had his project awarded funding through QISE-NET, the Quantum Information Science and Engineering Network. Run through the University of Chicago, QISE-NET is open to any student pursuing an advanced degree in any field of quantum science. Liu and other students in his cohort earn up to three years of support, including funding, mentoring and training at annual workshops. All awardees are paired with a mentoring QISE company or national lab, at which they will complete part of their projects. Liu describes his project, below. Cecilia Vollbrecht, a grad student in Chemistry, also earned this honor. Both Liu and Volbrecht are students in the Wisconsin Quantum Institute.
The Single Flux Quantum (SFQ) digital logic family has been proposed as a scalable approach for the control of next-generation multiqubit arrays. With NIST’s strong track record in the field of SFQ digital logic and the expertise of McDermott’s lab in the superconducting qubit area, we expect to achieve high fidelity SFQ-based qubit control. The successful completion of this research program will represent a major step forward in the development of a scalable quantum-classical interface, a critical component of a fully error-corrected fault-tolerant quantum computer.
New study provides understanding of astrophysical plasma dynamics
Stars, solar systems, and even entire galaxies form when astrophysical plasma — the flowing, molten mix of ions and electrons that makes up 99% of the universe — orbits around a dense object and attaches, or accretes, on to it. Physicists have developed models to explain the dynamics of this process, but in the absence of sending probes to developing stars, the experimental confirmation has been hard to come by.
In a study published in Physical Review Letters September 25, University of Wisconsin–Madison physicists recreated an astrophysical plasma in the lab, allowing them to investigate the plasma dynamics that explain the accretion disk formation. They found that electrons, not the momentum-carrying ions, dominate the magnetic field dynamics in less dense plasmas, a broad category that includes nearly all laboratory astrophysical plasma experiments.
Like water swirling around and down an open drain, plasma in an accretion disk spins faster nearer the heavy object in the center than further away. As the plasma falls inward, it loses angular momentum. A basic physics principle says that angular momentum needs to be conserved, so the faster rotating plasma must be transferring its momentum away from the center.
“This is an outstanding problem in astrophysics — how does that angular momentum get transported in an accretion disk?” says Ken Flanagan, a postdoctoral researcher with the department of physics at UW–Madison and lead author of the study.
The simplest explanation is friction, but it was ruled out when the corresponding accretion times, in some cases, would be longer than the age of the universe. A model developed by theoretical physicists posits that turbulence, or the chaotic changes in plasma flow speeds, can explain the phenomenon on a more realistic time scale.
“So ad hoc, astrophysicists say, ‘Okay, there’s this much turbulence and that explains it,’” Flanagan says. “Which is good, but you need to call in the plasma physicists to piece together where that turbulence comes from.”
Flanagan and colleagues, including UW–Madison physics professor Cary Forest, wanted to build off an idea that the turbulence was coming from an intrinsic property of some plasmas known as magnetorotational instability. This instability is seen in plasmas that are flowing fastest near the center and are in the presence of a weak magnetic field.
“And it’s lucky because there are weak magnetic fields all around the universe, and the flow profile in the accretion disks is set by the gravitational force,” Flanagan says. “So, we thought this plasma instability could be responsible for turbulence, and it explains how accretion disks work.”
To investigate if this intrinsic plasma instability explained the observation, the researchers turned to the Big Red Ball (BRB), a three-meter-wide hollow sphere with a 3000 magnets at its inner surface and various probes inside. They activate a plasma by ionizing gas inside the BRB, then applying a current to drive its movement.
Because they had previously been encountering problems in driving very fast flows, they tried a new technique to drive the flow across the entire volume of plasma, as opposed to just the edges. Fortuitously, the BRB had magnetic field probes from a previous experiment still attached, and when they activated the plasma under these conditions, they found that this new flow setup amplified the magnetic field strength with a peak at the center nearly twenty times the baseline strength.
“We didn’t expect to see that at all, because usually in plasma physics the simplest model is to think of plasmas as one fluid with the heavier ions dominating momentum,” Flanagan says. “The results suggested that the plasma is in the Hall regime, which means the electrons and their motion are entirely responsible for the plasma moving around magnetic fields.”
If they were correct in assuming it was the Hall effect that was driving magnetic field amplification, the equations governing magnetic fields and electric currents say that if you drive the current in the opposite direction, the strength of the magnetic field would be canceled out. So, they switched the current and measured the magnetic field strength: it was zero, supporting the Hall regime explanation.
While the results are not directly applicable to the plasma accretion disks around, say, a very dense black hole, they do directly impact the earth-bound experiments that attempt to recreate and study them.
“Nearly all plasma astrophysical experiments operate in the Hall regime, and so this sort of large qualitative effect is something you’re going to have to pay attention to when you make these sorts of flows in laboratory astrophysical plasmas,” Flanagan says. “In that sense, this work has a pretty broad impact for lots of different research areas.”
This research was supported in part by the National Science Foundation (#1518115) and by the U.S. Department of Energy (#DE-SC0018266).
Physics grad students share hands-on physics, art lessons with local fifth graders
UW–Madison physics grad student Aedan Gardill has been illustrating physics concepts with art for years, such as through his Instagram account, where he shares ink drawings. Earlier this year, he applied for a grant from the Madison Arts Commission to create hidden portraits of women in the physical sciences that could only be revealed by using polarized lenses. He also planned to visit local schools to explain the concept behind his art and help students make their own images based on his technique.
By the time Gardill learned he had been awarded the grant, the pandemic was in full force, and his plans had to change. While he could still present his portraits at the Wisconsin Science Festival, school visits were no longer in the cards.
“With the realization this summer that school was going to most likely be online in the fall, I had to rethink how I was going to use the funding from the grant,” Gardill explains. “And that has morphed into providing at-home, hands-on learning experiences that we’ll lead virtually.”
Funding for Gardill’s work is provided by a grant from the Madison Arts Commission, with additional funds from the Wisconsin Arts Board, the Optical Society of America, the International Society for Optics and Photonics, and the UW–Madison Department of Physics, with special thanks to Arts + Literature Laboratory. UW–Madison physics graduate student volunteers include Abby Bishop, Praful Gagrani, Jimena Gonzalez, Ben Harpt, Preston Huft, Brent Mode, Bryan Rubio Perez, Susan Sorensen, and Jessie Thwaites.
The J.J. Sakurai Prize is considered one of the most prestigious annual prizes in the field of theoretical high energy physics. Barger, who joined the UW–Madison faculty in 1965, is a world leader in theoretical particle physics where theory meets experiment. He is one of the founders of collider phenomenology as it is practiced today.
“This prize belongs to the hundreds of students, postdocs, faculty and visiting colleagues who entered the portal of UW–Madison to discover the quarks, leptons and bosons of particle physics,” Barger says. “Only at UW–Madison could this research at the interface of theory and experiment so thrive.”
The techniques that Barger helped develop have been crucial in establishing the experimental foundations of the Standard Model of particle physics and in guiding the search for signals of new physics. His contributions have played a key role in many important milestones in particle physics, including the discovery of the W boson in 1985, the top quark in 1995, and the Higgs boson discovery in 2012.
UW–Madison physics professor Lisa Everett and University of Hawaii professor Xerxes Tata, both phenomenologists, co-nominated Barger for the prize.
“We are thrilled that Vernon Barger has been awarded the 2021 J.J. Sakurai Prize, for which we nominated him for his seminal accomplishments and leadership record in collider physics phenomenology over five decades in the field,” Everett says. “The techniques he has pioneered have and continue to be of pivotal importance for elucidating physics signals at particle colliders, and these contributions are only part of a very long and distinguished research career in theoretical particle physics. He is highly deserving of this honor.”
Robert McDermott elected Fellow of the American Physical Society
Congratulations to Prof. Robert McDermott, who was elected a 2020 Fellow of the American Physical Society! He was elected for seminal contributions to quantum computing with superconducting qubits, including elucidating the origins of decoherence mechanisms, and development of new qubit control and readout methods. He was nominated by the Division of Quantum Information.
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.
Massive halo finally explains stream of gas swirling around the Milky Way
The Large and Small Magellanic Clouds are satellite galaxies of the Milky Way. They are surrounded by a high-velocity gaseous structure called the Magellanic Stream, which consists of gas stripped from both clouds. So far, simulations have been unable to reconcile observations with a complete picture of how the stream was formed. In this Nature week’s issue, numerical simulations carried out at by Scott Lucchini, graduate student at the Physics Department working with Elena D’Onghia, present a model that potentially resolves this conundrum. By embedding the Large Magellanic Cloud in a corona of ionized gas, the researchers were able to simulate the Magellanic Stream accurately and explain its structure. Ellen Zweibel and Chad Bustard are also co-authors of the article.