X(ray) marks the spot in elemental analysis of 15th century printing press methods

a woman (left, bending down) and a man (right, crouched) position an ancient manuscript into a machine

This story was originally published by University Communications

In 15th century Germany, Johannes Gutenberg developed a printing press, a machine that allowed for mass production of texts. It is considered by many to be one of the most significant technological advancements of the last millennium.

Though Gutenberg often receives credit as the inventor of the printing press, sometime earlier, roughly 5,000 miles away, Koreans had already developed a movable-type printing press.

There is no question that East Asians were first. There is also no question that Gutenberg’s invention in Europe had a far greater impact.

“What is not known is whether Gutenberg knew about the Korean printing or not. And if we could shed light on that question, that would be earth shattering,” says Uwe Bergmann, a professor of physics at the University of Wisconsin–Madison who, with UW–Madison physics graduate student Minhal Gardezi, is part of a large, interdisciplinary team that is analyzing historical texts.

He adds: “But even if we don’t, we can learn a lot about early printing methods, and that will already be a big insight.”

These texts include pages from a Gutenberg bible and Confucian texts, and they’re helping investigate these questions. The team includes 15th century Korean texts experts, Gutenberg experts, paper experts, ink experts and many more.

a person, with essentialy just their hands visible, holds a wooden box that is wrapped with a leather tie and has Korean text on the side
One of the leaves scanned was printed by a Korean movable type printing press in 1442. One of the team members from UNESCO, Angelica Noh, traveled with the preserved documents from Korea to SLAC. IMAGE PROVIDED BY MINHAL GARDEZI

How did two physicists end up participating in a seemingly very non-physics cultural heritage project? Bergmann had previously worked on other historical text analyses, where he pioneered the application of a technique known as X-ray fluorescence (XRF) imaging.

In XRF imaging, a powerful machine called a synchrotron sends an intense and very small X-ray beam — about the diameter of a human hair — at a page of text at a 45-degree angle. The beam excites electrons in the atoms that make up the text, requiring another electron to fill in the space left by the first (all matter is made up of atoms, which contain even smaller components called electrons).

The second electron loses energy in the process, and that energy is released as a small flash of light. A detector placed strategically nearby picks up that light, or its X-ray fluorescence, and measures both its intensity and the part of the light spectrum to which it belongs.

“Every single element on the periodic table emits an X-ray fluorescence spectrum that is unique to that atom when hit with a high-energy X-ray. Based on its ‘color,’ we know exactly which element is present,” says Gardezi. “It’s a very high-precision instrument that tells you all the elements that are at every location in a sample.”

With this information, researchers can effectively create an elemental map of the document. By rapidly scanning a page across the X-ray beam, they can create a record of the XRF spectrum at each pixel. One page can produce several million XRF spectra.

This summer, Bergmann and Gardezi were part of a team that used XRF scanning at the SLAC National Accelerator Laboratory in California to produce elemental maps of several large areas from original pages of a first-edition, 42-line Gutenberg Bible (dating back to 1450 to 1455 A.D.) and from Korean texts dating back to the early part of that. century.

They scanned the texts at a rate of around one pixel every 10 milliseconds, then filtered the data by elemental signature, providing high-resolution maps of which elements are present and in what relative quantities.

a three panel image. The top shows a regular photograph of the Korean text, with a dotted white line around two lines of 6 characters. The second panel shows the XRF of those characters, with a blue backround, a yellow-green hue aorund the characters, and red in the characters themmselves. The bottom panel shows a second XRF scan, but here almost the entire panel is blue, except for the circles of the characters, which are red, indicating the element being filtered was only present in the circles of the text.
A photograph of a scanned Korean text. The white dotted box indicates the areas shown in the middle and bottom panels. Each element produces a unique X-ray fluorescence. After scanning the text, the researchers applied filters for the known XRF patterns of different elements and created a color-coded heat-map of their abundance, from lowest (blue) to highest (red). An element found in only small quantities is in the red circles in the bottom part of the image. IMAGE PROVIDED BY MINHAL GARDEZI

In a way, the work is like digging for treasure from an old map — Gardezi says the researchers do not know exactly what they are looking for, but they are most interested in the unexpected.

For example, she recently presented early results of scans to the team, to demonstrate the approach had worked and that the researchers could separate out different elements. It turns out this isn’t what the team found most interesting.

“Instead, these scholars spent 15-to-20 minutes talking about, ‘Why is (this element) present?’ and coming up with hypotheses,” Gardezi says. “As physicists, we wouldn’t even recognize if something is surprising or not. It’s really this interdisciplinary aspect that tells us what to look for, what the smoking gun is.”

As more questions arise based on the elemental analyses, Bergmann and Gardezi will help guide the team to address those questions quantitatively. They are already planning to recreate some early printings in the lab — with known types, papers and inks — then compare these XRF scans with the originals.

The research may never definitively determine if Gutenberg knew about the Korean presses or if he developed his press independently. But without access to the original presses themselves, these texts hold the only clues to understanding the nature of these transformative machines.

“The more you read about it, the more you learn that there is less certainty about several things related to early printing presses,” Bergmann says. “Maybe this technique will allow us to view these prints as a time capsule and gain invaluable insight into this watershed moment in human history.”

Watch Minhal Gardezi show off XRF at SLAC National Accelerator Laboratory.

The UW–Madison efforts in the project are supported by the Overseas Korean Cultural Heritage Foundation.

Coherent light production found in very low optical density atomic clouds

No atom is an island, and scientists have known for decades that groups of atoms form communities that “talk” to each other. But there is still much to learn about how atoms — particularly energetically excited ones — interact in groups.

In a study published in PRX Quantum, physicists from the University of Wisconsin–Madison observed communication between atoms at lower and lower densities. They found that the atoms influence each other at 100 times lower densities than probed before, exhibiting slow decay rates and emitting coherent light.

“It seems that (low-density) groups of excited atoms spontaneously organize to then produce light that is coherent,” says David Gold, a postdoctoral fellow in Deniz Yavuz’s group and lead author of the study. “These findings are pretty interesting from a basic science standpoint, and in terms of quantum computing, the takeaway is that even with very low numbers of atoms, you can see significant amounts of (these effects).”

A well-established property of atoms is found in electron excitation: when a specific wavelength of light hits an atom of a specific element, an electron is excited to a higher orbital level. As that electron decays back to its initial state, a photon of a specific wavelength is emitted. A single atom has a characteristic decay rate for that process. When groups of atoms are studied, their interactions are observed: the initial decay rate is very fast, or superradiant, then transitions to a slower, or subradiant, rate.

A schematic of the experimental setup. (Top) the overall apparatus used. (A) shows the setup for the first part of the experiment, where the researchers were measuring decay rates in lower and lower density clouds. (B) shows the setup for the second part of the paper, with the addition of an interferometer

Though well-established in dense clouds, this group-talk has never been studied in less dense clouds of atoms, which could have impacts on applications such as quantum computing.

In their first set of experiments, Gold and colleagues asked what the decay rate of lower-density clouds looked like. They supercooled the atoms in a cloud, hit them with an excitation laser, and recorded the decay rates as an intensity of emitted light over time. They observed the characteristic subradiance. In this case, they did not always see superradiance, likely due to the reduced number of atoms available to measure.

profile picture of David Gold
David Gold

Next, they asked what happened if they let the cloud expand — or decrease in density — for varying periods of time before repeating their experiment. They found that as the cloud become less and less dense, the amount of subradiance decreased, until eventually a density was reached where the atoms stopped behaving like a group and instead displayed single-atom decay rates.

“The most subradiance that we observed was at around a hundred times lower optical density than it had previously been observed before,” Gold says.

Now that the researchers knew that a less dense cloud still decays subradiantly to a point, they asked if the decay was happening in an isolated manner, or if the atoms were really acting as a group. If acting as a group, the emitted light would be coherent, or more laser-like, with some structure between the atoms.

They used the same experimental setup but added an interferometer, where light is split and recombined before the photons are detected. They first set the baseline interference pattern by moving the mirror closer or further away from the splitter — changing the path length of one of the beams — and mapping the interference pattern of the split light waves that were emitted from the same atom.

If there were no relationship between the two atoms and the light they emit, then they would have expected to see no interference pattern. Instead, they saw that for some distance of mirror displacement, the lightwaves did interfere, indicating that different atoms being measured were nonetheless producing coherent light.

“I think this is the more exciting thing we found: that the light that’s being emitted is coherent and it has more of the properties of a laser than you would expect,” Gold says. “The atoms are influenced by each other and not in a way we would have expected.”

Aside from the interesting physics seen in the study, Gold says the work is also applicable to quantum computing, particularly as those computers grow bigger in the future.

“Even if everything in a quantum computer is running perfectly and the system was completely isolated, there’s still this inherent thing of, well, the atoms just might decay down from [the computational] state,” Gold says.

This work was supported by National Science Foundation (NSF) Grant No. 2016136 for the QLCI center Hybrid Quantum Architectures and Networks.

Detailed analysis of old star provides template for heavy element formation

This story was originally published by University Communications

The fusion furnaces that are the universe’s stars create the elements from helium up to iron. But iron is only number 26 on the periodic table out of well over 100 known elements. So the heavier ones, like gold, lead and uranium, must come from somewhere other than fusion.

Scientists have long known that those heavy elements come from neutron capture, where neutrons are added to an element that make it unstable, then it radioactively decays and its atomic number increases by one. Nearly 70 years ago, they confirmed one site, or event, of a neutron capture method known as the slow, or s-process. The rapid, or r-process, was not confirmed with a site until 2017, when the LIGO/VIRGO collaboration detected a neutron star merger.

“With a neutron star merger, the neutron stars are ripped apart and they throw out neutrons, and you can build lots of heavy elements out of these neutron stars,” says Jim Lawler, a professor of physics at the University of Wisconsin–Madison. “The mystery arises when we look at the total r-process inventory of our home galaxy: Can we explain all that with neutron star mergers or are there additional sites?”

In a new study led by astronomers from the University of Michigan, Lawler and colleagues identified the elemental composition of HD 222925, a Milky Way star located over 1400 lightyears from earth. Their analysis confirmed that the star was rich in r-process elements, and they were able to identify and calculate the relative abundance of each element. They also found that the star is iron- and metal-poor, a proxy for age that indicates HD 222925 is relatively old and provides information about early star formation.

“We were able to determine a complete r-process abundance pattern for what we think is probably one event that happened early in the beginning of the universe,” Lawler says. “So that r-process template now can be used to screen various models of the nuclear physics that produce the r-process and see if the models for all sites are physically correct.”

At UW–Madison, Lawler and scientist Elizabeth Denhartog contributed the spectroscopic analysis that identified the elements in the star. Every element has a unique electromagnetic spectrum that can be separated into spectral lines using a diffraction grating — just like a prism separates white light into a rainbow. HD 222925 is a relatively bright star, meaning it provided stronger spectra to analyze. It was also identified by the Hubble Space Telescope, providing access to data in the ultraviolet range that is normally blocked by the ozone layer and undetectable by telescopes on Earth.

For the full story, read more on the University of Michigan’s news site.


Researchers aim X-rays at century-old plant secretions for insight into Aboriginal Australian cultural heritage

This story was originally published by David Krause at SLAC

For tens of thousands of years, Aboriginal Australians have created some of the world’s most striking artworks. Today their work continues long lines of ancestral traditions, stories of the past and connections to current cultural landscapes, which is why researchers are keen on better understanding and preserving the cultural heritage within.

close up of a tall, narrow, spiky brown plant
Secretions called exudate cover parts of the spike of a Xanthorrhoea plant — colloquially called “grass tree” or “yakka” — used in aboriginal art. PHOTO COURTESY FLINDERS UNIVERSITY, SOUTH AUSTRALIA

In particular, knowing the chemical composition of pigments and binders that Aboriginal Australian artists employ could allow archaeological scientists and art conservators to identify these materials in important cultural heritage objects. Now, researchers are turning to X-ray science to help reveal the composition of the materials used in Aboriginal Australian cultural heritage – starting with the analysis of century-old samples of plant secretions, or exudates.

Aboriginal Australians continue to use plant exudates, such as resins and gums, to create rock and bark paintings and for practical applications, such as hafting stone points to handles. But just what these plant materials are made of is not well known.

Therefore, scientists from six universities and laboratories around the world turned to high-energy X-rays at the Stanford Synchrotron Radiation Lightsource (SSRL) at the Department of Energy’s SLAC National Accelerator Laboratory and the synchrotron SOLEIL in France. The team aimed X-rays at ten well-preserved plant exudate samples from the native Australian genera EucalyptusCallitrisXanthorrhoea and Acacia. The samples had been collected more than a century ago and held in various institutions in South Australia.

The results of their study were clearer and more profound than expected.

“We got the breakthrough data we had hoped for,” says Uwe Bergmann, physicist at the University of Wisconsin–Madison and former SLAC scientist who develops new X-ray methods. “For the first time, we were able to see the molecular structure of a well-preserved collection of native Australian plant samples, which might allow us to discover their existence in other important cultural heritage objects.”

Researchers today published their results in the Proceedings of the National Academy of Sciences.

Profile picture of Uwe Bergmann
Uwe Bergmann

Looking below the surface

Over time, the surface of plant exudates can change as the materials age. Even if these changes are just nanometers thick, they can still block the view underneath it.

“We had to see into the bulk of the material beneath this top layer or we’d have no new information about the plant exudates,” SSRL Lead Scientist Dimosthenis Sokaras says.

Conventionally, molecules with carbon and oxygen are studied with lower-energy, so-called “soft” X-rays, that would not be able to penetrate through the debris layer. For this study, researchers sent high-energy X-ray photons, called “hard” X-rays, into the sample. The photons squeezed past foggy top layers and into the sample’s elemental arrangements beneath. Hard X-rays don’t get stuck in the surface, whereas soft X-rays do, Sokaras says.

Once inside, the high-energy photons scattered off of the plant exudate’s elements and were captured by a large array of perfectly aligned, silicon crystals at SSRL. The crystals filtered out only the scattered X-rays of one specific wavelength and funneled them into a small detector, kind of like how a kitchen sink funnels water drops down its drain.

Next, the team matched the wavelength difference between the incident and scattered photons to the energy levels of a plant exudate’s carbon and oxygen, providing the detailed molecular information about the unique Australian samples.

5 brown glass jars with pigment samples outside of them
Century-old plant exudate samples in amber jars. Researchers mapped the chemistries of these samples using high-energy photons, knowledge that will help study and preserve the work of aboriginal artists who used plant material. PHOTO COURTESY FLINDERS UNIVERSITY, SOUTH AUSTRALIA

A path for the future

Understanding the chemistries of each plant exudate will allow for a better understanding of identification and conservation approaches of Aboriginal Australian art and tools, Rafaella Georgiou, a physicist at Synchrotron SOLEIL, said.

“Now we can go ahead and study other organic materials of cultural importance using this powerful X-ray technique,” she says.

Researchers hope that people who work in cultural heritage analysis will see this powerful synchrotron radiation technique as a valuable method for determining the chemistries of their samples.

“We want to reach out to that scientific community and say, ‘Look, if you want to learn something about your cultural heritage samples, you can come to synchrotrons like SSRL,’” Bergmann says.

SSRL is a DOE Office of Science user facility. In addition to SSRL, parts of this research were carried out at SOLEIL in France and three CNRS laboratories (PPSM, IPANEMA, IMPMC). The University of Pisa, the Université Paris-Saclay, the University of Melbourne, Flinders University, the Australian Synchrotron International Synchrotron Access Program, and other organizations also supported this research.

Congratulations to Professor Lawler on his retirement!

After 42 years on the UW–Madison faculty, Jim Lawler, the Arthur and Aurelia Schawlow Professor of Physics, has announced his retirement. Lawler is an atomic, molecular & optical physicist with a focus developing and applying laser spectroscopic techniques for determining accurate absolute atomic transition probabilities. His retirement is official as of May 22.

“What we’ve really done gradually over four-plus decades is make atomic spectroscopy more quantitative so that people can use it to really learn the detailed physics and chemistry of the remote universe,” Lawler says.

Lawler received his MS (’74) and PhD (’78) from this department, studying with now-professor emeritus Wilmer Anderson. In the two years after earning his doctorate, he was a research associate at Stanford University, and returned to UW–Madison as an assistant professor in 1980.

“There was a little bit of a disadvantage to come back to a place where I had recently been as a student,” Lawler says. “But I knew I would get extremely good graduate students and I would have access to a lot of infrastructure, and that combination really drew me back.”

He had extremely good graduate students and postdocs. Lawler supervised 26 PhD students and 10 terminal MS students. Those students and postdocs have gone on to prestigious National Research Council Fellowships, group lead positions at major companies, and tenured professorships, amongst many others.

Lawler served as department chair from 1994-1997. He also accumulated numerous awards and honors over his distinguished career. He is a fellow of the American Physical Society, the Optical Society of America, the U.K. Institute of Physics, and in 2020 he was elected a Legacy Fellow of the inaugural class of American Astronomical Society Fellows. He won the 1992 W. P. Allis Prize of the American Physical Society and the 1995 Penning Award from the International Union of Pure and Applied Physics for research in plasma physics, the two highest National and International Awards in the field of Low Temperature Plasma Physics. In 2017, he won Laboratory Astrophysics Prize of the American Astronomical Society for research in spectroscopy.

Longtime collaborator Blair Savage, UW–Madison professor emeritus of astronomy, says:

“Jim’s work in laboratory astrophysics provided extremely important atomic ultraviolet transition probabilities in support of the Hubble Space Telescope programs to determine elemental abundances of gaseous matter in the interstellar medium from three different ultraviolet spectrographs over the 32-year history of the space observatory. They included the Goddard High Resolution Spectrograph, the Space Telescope Imaging Spectrograph and the Cosmic Origins Spectrograph.”

And Wilmer Anderson, Lawler’s doctoral advisor, says:

“He was a very good graduate student, and he of course has turned out to be a really great scientist and colleague. His lifetime measurements on atomic physics played a key role in understanding the neutron star collisions. I’m sorry to see him retiring but I’m sure that he will leave a legacy behind that’s really fantastic. It’s going to be a big loss to the department not to have him around.”

Lawler has collaborated with his AMO colleagues over the years, but in more of an intellectual capacity than in research. As he notes, much of AMO is headed in the quantum information and quantum computing direction, with public and private funding helping to drive it. Still, he does not see AMO headed solely in the quantum direction.

“Decades from now the currently Hot areas of physics will be less glamorous, but those stars are still going to be light years away,” Lawler says. “I think the connection of astronomy and spectroscopy — the way we learn about the physics and chemistry of the remote universe — is strong enough that it will survive. And helping make spectroscopy in astronomy more quantitative is what we’ve done that will have some lasting significance.”


Alex Levchenko awarded NSF condensed matter and materials theory grant

Congrats to Alex Levchenko on his funded NSF proposal, Electronic phases and transport in quantum matter at strong coupling. It was funded through the Division of Materials Research, condensed matter and materials theory program.

According to the non-technical summary:

This award supports theoretical research on quantum materials where the strong electron-electron interaction leads to unique transport, thermodynamic and magnetic properties. The research agenda addresses both fundamental physics of electronic interactions in complex materials and practical physics of mesoscopic devices relevant for applications in the domain of quantum science with micro and nanostructures.

The conversion of heat into electricity in solid state systems is governed by thermoelectric effects. The thermoelectric transport in quantum materials and devices is at the heart of various modern electronics applications. Over the last decade, transport measurements in atomically thin two-dimensional materials, such as graphene composed of a single layer of carbon atoms, provided overwhelming evidence that the flow of electrons in such systems exhibits hydrodynamic behavior that resembles the flow of a viscous fluid. These advances pushed the limits of hydrodynamics, providing new perspectives on old fundamental problems and opening doors for completely new discoveries of emergent physics phenomena. This project is, in part, devoted to new research on thermoelectric resistance of such systems as they are subjected to magnetic fields. The PI will also extend these studies to other forms of low-temperature electronic behavior in solids such as superconductivity, where electrons flow without any resistance, and magnetism, as well as their coexistence.

This award also supports the PI’s educational and outreach activities. The project places significant emphasis on training graduate and undergraduate students by engaging them in research in a highly collaborative environment with a postdoctoral scholar and colleagues from other groups. The PI will reach out to the public and high-school student audiences through (i) collaboration with the USA Physics Olympiad team to foster new generation of physicists and train high-school students for international scholastic competition and (ii) public education via entertaining Wonders of Physics shows. The PI will also be involved in the scientific coordination of a physics summer school as well as organization of international conferences and workshops.

Fringe benefits: new technique makes x-rays more laser-like

Detecting a chemical change is often easy: colors may change, heat may be released, or something may smell different. Seeing reactions at the molecular level is not quite so easy, but knowing exactly when and how chemical bonds form or atoms move around is crucial to understanding chemical processes.

animated gif showing atomic-level structural changes taking place during the chemical reaction
X-ray pulses allow researchers to create real-time movies of chemical reactions at the molecular scale (click on image to see animation)

In a new study published March 15 in Proceedings of the National Academy of Sciences, University of Wisconsin–Madison physics professor Uwe Bergmann and his collaborators have turned ultrafast x-ray pulses into something more akin to an optical laser, with cleaner, directional pulses. Their work may lead to visualizing chemical reactions faster than ever at the atomic scale.

“This work is the first step to do with x-rays the same kind of [techniques] which you do with regular lasers,” says Bergmann, the study’s senior author. “We have opened a time window for looking at chemical processes with attosecond [one billionth of one billionth of a second] precision. It’s a new frontier.”

Profile picture of Uwe Bergmann
Uwe Bergmann

Around a decade ago, researchers began using powerful x-ray free-electron lasers, which allow them to make ultrafast movies of molecular changes in real time on the femtosecond scale (one thousand times slower than an attosecond). Compared to visible lasers, which provide clean, single-wavelength beams of light, x-ray lasers are somewhat dirty: they contain multiple wavelengths of light of randomly varying intensity.

“What all scientists have done, and are still doing, is that you just adapt to what you get and then you design your experiments around them,” Bergmann says. “That also means that certain experiments, which in the optical laser regime are now standard, have not been possible.”

Bergmann and his colleagues somewhat accidentally discovered a way to make x-rays more like an optical laser. In their experimental setup, they shine intense but dirty x-ray pulses at a manganese sample. When these pulses hit a manganese atom, a lower-level electron is ejected and the hole it leaves is rapidly filled by a higher-level electron. The energy difference is emitted as a photon of a characteristic color. Very intense pulses can create enough of these holes. An emitted photon can effectively stimulate the emission of another one, leading to an avalanche of stimulated X-ray emission, mostly in the forward direction towards their detector.

Every so often, the detector that captures these stimulated emissions showed something they were not expecting: strong fringes, the characteristic pattern that results from constructively and destructively interfering signals. The fringes suggested that they had observed two x-ray emission pulses, separated by only a few femtoseconds.

“We were confused,” Bergmann says. “How did such a pair of x-ray pulses come about?”

After many discussions, calculations, and simulations, the team ruled out many possible explanations, until they finally realized what had happened: occasionally, two of the many spikes in the dirty pulses were much stronger than the rest of them. When these strong spikes occurred a few femtoseconds apart, and each had enough intensity, a clean pair of stimulated x-ray emission pulses emerged.

depiction of the experiment: a pulse of x-rays is shown as jagged white peaks. that pulse travels through the sample, represented as a thin square, where the signals are stimulated into larger, unidirectional peaks, shown as a red and yellow taller peaks. those peaks are streched out length-wise by the monochromator such that they now overlap. The result is a rainbow-colored splotch representing intensity of the measured signal. The splotch looks like a comb, which are the fringes.
Two strong x-ray pulses hit the manganese sample, are stretched through the monochromator, and overlap, leading to the characteristic fringes.

Before these two pulses reach the detector, they first travel through a monochromator — essentially a prism that stretches light, much like how white light passing through a clear prism is stretched into a rainbow. These stretched pulses then overlap timewise, and those frequencies that are in phase with each other can add up to become more intense or cancel each other out into dark troughs. Hence, the fringes.

“At times, each signal is rather clean and of similar strength, and one obtains very strong interference fringes,” Bergmann says. “We know that the fringe spacings are directly related to the time difference of the two pulses, and because we can measure them very precisely, we can obtain their time difference with extreme, attosecond precision.”

Currently, these pulse pairs are generated very rarely, Bergmann and his collaborators will work with the accelerator scientists to find ways to manipulate the ‘dirty’ pulses and enhance the chance of producing the pairs. They are optimistic that their work opens the door to new applications of such x-ray pulse pairs — the types of techniques that are used commonly with visible laser light.

“We’re trying to move nonlinear laser optics into the x-ray regime,” Bergmann says. “In the x-ray regime, you can probe certain phenomena that you just cannot optically access. X-ray wavelengths are comparable to the distances between atoms, and we can knock out lower-level electrons to get element specificity with them.”

Bergmann’s contribution to this research was funded in part by the U.S. Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory (DE-AC02-76SF00515). Other authors were supported by various funding as described in the study.

Ultraprecise atomic clock poised for new physics discoveries

University of Wisconsin–Madison physicists have made one of the highest performance atomic clocks ever, they announced Feb. 16 in the journal Nature.

Their instrument, known as an optical lattice atomic clock, can measure differences in time to a precision equivalent to losing just one second every 300 billion years and is the first example of a “multiplexed” optical clock, where six separate clocks can exist in the same environment. Its design allows the team to test ways to search for gravitational waves, attempt to detect dark matter, and discover new physics with clocks.

optical video of a ball of strontium atoms being mutliplexed into 6 separate, smaller spheres of atoms, like pearls along a string
From one sphere of supercooled strontium atoms, Kolkowitz’s group multiplexes them into six separate spheres, each of which can be used as an atomic clock.

“Optical lattice clocks are already the best clocks in the world, and here we get this level of performance that no one has seen before,” says Shimon Kolkowitz, a UW–Madison physics professor and senior author of the study. “We’re working to both improve their performance and to develop emerging applications that are enabled by this improved performance.”

Atomic clocks are so precise because they take advantage of a fundamental property of atoms: when an electron changes energy levels, it absorbs or emits light with a frequency that is identical for all atoms of a particular element. Optical atomic clocks keep time by using a laser that is tuned to precisely match this frequency, and they require some of the world’s most sophisticated lasers to keep accurate time.

By comparison, Kolkowitz’s group has “a relatively lousy laser,” he says, so they knew that any clock they built would not be the most accurate or precise on its own. But they also knew that many downstream applications of optical clocks will require portable, commercially available lasers like theirs. Designing a clock that could use average lasers would be a boon.

Read the full story

Shimon Kolkowitz one of four UW professors awarded Sloan Fellowship

Four University of Wisconsin–Madison professors, including assistant professor of physics Shimon Kolkowitz, have been named to Sloan Research Fellowships — competitive, prestigious awards given to promising researchers in the early stages of their careers.

“Today’s Sloan Research Fellows represent the scientific leaders of tomorrow,” says Adam F. Falk, president of the Alfred P. Sloan Foundation, which has awarded the fellowships since 1955. “As formidable young scholars, they are already shaping the research agenda within their respective fields—and their trailblazing won’t end here.”

Kolkowitz, an assistant professor of physics, builds some of the most precise clocks in the world by trapping ultracold atoms of strontium — clocks so accurate they could be used to test fundamental theories of physics and search for dark matter.

UW–Madison’s other 2022 Sloan Fellows are Tatyana Shcherbina (math), Zachary K. Wickens (chemistry) and Andrew Zimmer (math).

The UW–Madison professors are among 118 researchers from the United States and Canada honored by the New York-based philanthropic foundation. The four new fellows join 110 UW–Madison researchers honored in the past.

Each fellow receives $75,000 in research funding from the foundation, which awards Sloan Research Fellowships in eight scientific and technical fields: chemistry, computer science, economics, mathematics, computational and evolutionary molecular biology, neuroscience, ocean sciences and physics.

Shimon Kolkowitz earns NSF CAREER award

profile photo of Shimon Kolkowitz
Shimon Kolkowitz

Shimon Kolkowitz has already developed one of the most precise atomic clocks ever. Now, the UW­­–Madison physics professor has been awarded a Faculty Early Career Development (CAREER) award from the National Science Foundation (NSF) to use his atomic clocks to potentially answer some big questions about the physics of our universe.

The five-year, $800,000 in total award will cover research expenses, graduate student support, and outreach projects based on the research.

“I am honored and proud to receive an NSF CAREER award, which will help my research group expand our experimental efforts and build upon our recent results,” Kolkowitz says. “This award will support research into new ways to harness the remarkable precision of optical atomic clocks for exciting physics applications such as searching for dark matter and detecting gravitational waves.”

optical video of a ball of strontium atoms being mutliplexed into 6 separate, smaller spheres of atoms, like pearls along a string
From one sphere of supercooled strontium atoms, Kolkowitz’s group multiplexes them into six separate spheres, each of which can be used as an atomic clock.

Atomic clocks are so precise because they take advantage of the natural vibration frequencies of atoms, which are identical for all atoms of a particular element. Kolkowitz and his research group have developed atomic clocks that can detect the difference in these frequencies between two clocks that would only disagree with each other by one second after 300 billion years, the tiniest detectable frequency changes to date. These clocks, then, can measure effects that shifts their frequency by only 0.00000000000000001%, opening the possibility of using them in the search for new physics.

A significant advancement in Kolkowitz’s clocks is that they are multiplexed, with six or more separate clocks in one

vacuum chamber, effectively placing each clock in the same environment. Mutliplexing means that comparisons between the clocks, and not their individual accuracy, is what matters — and allows the group to use commercially available, robust and portable lasers in their measurements. Though the clocks are not yet ready to be used to detect gravitational waves, Kolkowitz says the current setup “looks a bit like how you would eventually do that,” and will allow him to test out and demonstrate the concept.

In the spirit of the Wisconsin Idea and the NSF’s “broader impacts” to benefit society beyond scientific merit, with this award, Kolkowitz will focus efforts on quantum science outreach with pre-college students.

“We’ll be developing new demos and hands-on activities designed to introduce K-12 students to modern physics concepts,” Kolkowitz says. “We’ll use these activities to engage students at live shows and interactive events as part of The Wonders of Physics outreach program, with an emphasis on reaching rural and Native American communities in Wisconsin.”

NSF established these awards to help scientists and engineers develop simultaneously their contributions to research and education early in their careers. CAREER funds are awarded by the federal agency to junior-level faculty at colleges and universities.