Research Highlights

Simple, cost-effective trapped ion qubit technology developed

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Physics professor Mark Saffman, affiliate professor Mikhail Kats and their groups have developed a simplified but ingenious method for trapping atoms of different species to make quantum bits or qubits, they published in Science Advances.

Capturing two types of neutral atoms next to each other, the method creates interleaved grids of cesium and rubidium atoms that can be used as qubits in quantum computing and quantum sensing. The setup is much simpler and cost-effective than previous efforts and is already being used in early-stage quantum devices.

“Other groups have trapped two types of neutral atoms, but their setups are pretty sophisticated, use multiple lasers, and are expensive,” Kats says. “We have demonstrated that you can do this kind of trapping with a single laser and single micro-fabricated mask.”

As quantum computing emerges, there is no clear consensus on which material should be used to make the qubits which are the building blocks of quantum computers. Researchers are looking into qubits made of superconductors, diamond, trapped ions, and other specialized materials. But one relatively scalable qubit candidate is neutral atoms — those, like rubidium and cesium, that have a net zero electrical charge — that can be isolated, or “trapped,” using lasers.

All qubits are sensitive to their environment and need to stay as isolated from the outside world as possible so they maintain their quantum state: external influences can cause them to “decohere” and lose information. However, when the time is right, otherwise well-isolated qubits need to be able to interact with each other and with external inputs.

Trapping two types of neutral atoms next to each other is a promising approach to these seemingly contradictory requirements for components of quantum computers and quantum sensors. To isolate two types of atoms in the same space, the team fabricated a specialized optical mask using ultrathin layers of gold and the semiconductor germanium.

Sending a specific frequency range of laser light through this semitransparent mask divides it into a pattern of bright, dark, and intermediate areas, which interact to form the traps. The researchers filter and demagnify the light pattern before it enters a vacuum cell filled with cesium and rubidium atoms. Rubidium is attracted to the areas with high electromagnetic field, called bright traps. Conversely, the cesium migrates into the dark traps. The result is two sets of neutral atoms in distinct patterns in close proximity to each other.

These interleaved patterns of atoms can then be used for computing; one set of undisturbed atoms is for computation while the other set communicates commands and information with users. The atoms can also be used for sensing, with one set of atoms interacting with and collecting data from the environment while the other set records and processes the signals.

-Jason Daley, College of Engineering

Generating attosecond hard X-ray pulses

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Once only a part of science fiction, lasers are now everyday objects used in research, healthcare and even just for fun. Previously available only in low-energy light, lasers now come in wavelengths from microwaves through X-rays, opening up a range of different downstream applications.

In a study in Nature, a team led by UW–Madison scientists generated the shortest hard X-ray pulses to date through the first demonstration of strong lasing phenomena. The resulting pulses can lead to several potential applications, from quantum X-ray optics to visualizing electron motion inside molecules.

“We have observed strong lasing phenomena in inner-shell X-ray lasing and been able to simulate and calculate how it evolves,” says Uwe Bergmann, physics professor at UW–Madison, and senior author on the study.

The inner-shell X-ray lasing process is similar as it is in optical lasing, just at much shorter wavelengths. Because inner-shell electrons are tightly held, powerful X-ray pulses, like those from X-ray free-electron lasers (XFEL), are required to excite enough of them simultaneously to result in lasing. In turn, the photons they emit in this process are also at X-ray wavelengths. But XFEL pulses are generally “dirty,” with each pulse really being made of several short, intense spikes in time, and a range of spikes with different wavelengths, limiting some of their applications.

“They’re just not clean, beautiful pulses (like visible lasers),” says Thomas Linker, joint postdoctoral researcher at UW–Madison and the Stanford PULSE Institute at SLAC and lead author of the study. “But it’s the only thing we have.”

Here, the researchers tightly focused XFEL pulses onto a sample made of copper or manganese. The input pulse is still dirty, but very short and incredibly powerful: the equivalent of focusing all the sunlight that hits the Earth into one square millimeter. The emitted X-ray photons hit instrumentation that disperses them by wavelength, much like a prism disperses visible light into a rainbow, reflects it based on its angle, then is read by a detector.

Their results show that emitted light contained all of the expected wavelengths, but spatially, it showed a few hotspots instead of the expected smooth signal. Applying a 3D simulation, Linker calculated that the emitted X-rays underwent filamentation, a strong lasing phenomenon.

When they further increased the intensity of the input pulse, they saw another unexpected result: instead of seeing hotspots of one wavelength, they observed spectral broadening and sometimes multiple spectral lines. They ran the simulation on this new data and realized that this result can only be explained by another lasing phenomenon called Rabi cycling, where the pulse is so strong that the sample will cyclically absorb photons and emit them by stimulated emission. They used their simulation to plot the emitted pulse intensity over time and found that their dirty input pulses resulted in extremely short stimulated emission pulses — the shortest hard X-ray pulses observed by anyone to date.

“We have generated hard X-ray pulses, 60 to 100 attoseconds in duration, with these strong lasing phenomena,” Linker says.

An attosecond is one quintillionth of a second, and this extremely short pulse duration is what could drive new, advanced LASER applications. “If you want to see electron dynamics, how they move inside their orbitals, that’s the attosecond timescale,” Linker says.

Adds Bergmann: “There are so many nonlinear technologies and phenomena that the laser community uses now, but very few of those have dared to have been tried with hard X-rays. This work is a step towards pushing the exciting field of real laser science into this powerful hard X-ray regime.”

Vera C. Rubin Observatory celebrates first images, start of 10-year survey

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The first images of the greatest cosmic movie ever made were released by the Vera C. Rubin Observatory this past summer, and one of the “directors” was UW–Madison physics professor Keith Bechtol.

It’s a story a decade in the making for Bechtol, who served in a leadership role as the observatory’s System Verification and Validation Scientist and has been part of the international collaboration since 2016. He and his UW–Madison research group have been key players on a team of thousands of people that brought the observatory to the main stage. In 2025, its state-of-the-art telescope started taking the first images of the night sky.

“Rubin Observatory is a confluence of technology that allows us to map the universe faster than we’ve ever been able to before,” Bechtol says. “It will catalog more stars, galaxies, and Solar System objects during the first year of science operations than all previous telescopes combined. We will chronicle how the universe changes over time.”

Space-based telescopes like Hubble and James Webb typically focus on one spot for a prolonged time. In contrast, the ground-based Rubin Observatory, positioned on a mountaintop in Chile, is quickly scanning the sky, taking an image with its 3.2-billion-pixel camera every 40 seconds and collecting 20 terabytes of data each night. The observatory is running the “Legacy Survey of Space and Time,” capturing the entire southern hemisphere sky every three nights over its anticipated 10-year run.

In his role, Bechtol was one of five technical group leaders who organized the observatory’s commissioning effort — the building, implementation, and testing that happens on the way to a fully operating observatory. Bechtol oversaw the science deliverables of the project.

“I gather the evidence to show that all components of Rubin Observatory are working together to produce the most detailed time-lapse view of the cosmos ever made,” he says. “I’ve been responsible for anticipating things that could go wrong and helping to address those challenges, designing observation plans, rehearsing observatory operations, and implementing tests of increasing sophistication as we built the observatory. It’s been many years of preparation to get to this point.”

In April, Rubin Observatory achieved “first photon.” In June, people across the globe celebrated the release of the first images, including a viewing party in Chamberlin Hall.

Bechtol and his group will use the data to probe fundamental questions related to dark matter, dark energy, and the early universe.

“We’re using the whole universe as a laboratory to ask big, open questions about the nature of matter, energy, space, and time. What is the universe made of? How did the universe begin? How will it end?” Bechtol says. “We use measurements of strong and weak gravitational lensing and the clustering of galaxies to study dark energy, as well as so-called ultrafaint galaxies to learn about dark matter.”

By Sarah Perdue, Department of Physics