Shimon Kolkowitz awarded two grants to push optical atomic clocks past the standard quantum limit

a metalilc chamber with a blue glowing orb of illuminated atoms in the center

Optical atomic clocks are already the gold standard for precision timekeeping, keeping time so accurately that they would only lose one second every 14 billion years. Still, they could be made to be even more precise if they could be pushed past the current limits imposed on them by quantum mechanics.

With two new grants from the U.S. Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, UW–Madison physics professor Shimon Kolkowitz proposes to introduce quantum entanglement — where atoms interact with each other even when physically distant — to optical atomic clocks. The improved clocks would allow researchers to ask questions about fundamental physics, and they have applications in improving quantum computing and GPS.

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. These clocks operate at or near the standard quantum limit, a fundamental limit on performance imposed on clocks where the atoms are all independent of each other. The only way to push the clocks past that limit is to achieve entangled states, strange quantum states where the atoms are no longer independent and they become intertwined.

a cartoon showing the atoms in their pancakes as described in the text“That turns out to be hard for a number of reasons. Entanglement requires these atoms to interact with each other, but a good clock requires them not to interact with each other or anything else,” Kolkowitz says. “So, you need to engineer a situation where you can make the atoms interact strongly, but you can also switch those interactions off. And those are some of the same requirements that are necessary for quantum computing.”

Kolkowitz is already building an optical atomic clock in his lab, albeit one that is not yet using entangled states. To make the clock, they first laser-cool strontium atoms to one millionth of one degree Celsius above absolute zero, then load the atoms into an optical lattice. In the lattice, the atoms are separated into what is effectively a tiny stack of pancakes — each atom can move around within their own flat disk, but they cannot jump into another pancake.

Though the atoms’ are stuck in their own pancake, they can interact with each other if their electrons are highly excited. This type of atom, known as Rydberg atoms, becomes close to one million times larger than an unexcited counterpart because the excited electron can be microns away from the nucleus.

“It’s kind of crazy that a single atom can be that big, and when you make them that much bigger, they interact much more strongly with each other than they do in their ground states,” Kolkowitz says. “Basically it means you can go from the atoms not interacting at all to interacting very strongly. That’s exactly what you want for quantum computing, and it’s what you want for this atomic clock.”

With the two ARO grants, Kolkowitz expects to generate Rydberg atoms in his lab’s atomic clock. One of the grants, a Defense University Research Instrumentation Program (DURIP), will fund the specialized UV laser that generates the high energy photons needed to excite the atoms into the highly excited Rydberg states. The second grant will fund personnel and other supplies. Kolkowitz will collaborate with UW–Madison physics professor Mark Saffman, who, along with physics professor Thad Walker, pioneered the use of Rydberg atoms for quantum computing.

In addition to being useful for developing new approaches to ask questions about fundamental physics in his research lab, these ultraprecise atomic clocks are of interest to the Department of Defense for atomic clock-based technologies such as GPS, and because they can be used to precisely map Earth’s gravity.

Scientists Say Farewell to Daya Bay Site

The Daya Bay Reactor Neutrino Experiment collaboration – which made a precise measurement of an important neutrino property eight years ago, setting the stage for a new round of experiments and discoveries about these hard-to-study particles – has finished taking data. Though the experiment is formally shutting down, the collaboration will continue to analyze its complete dataset to improve upon the precision of findings based on earlier measurements.

The detectors for the Daya Bay experiment were built at UW–Madison by the Physical Sciences Laboratory, and detailed in a 2012 news release.

Says PSL’s Jeff Cherwinka, U.S. chief project engineer for Daya Bay:

The University of Wisconsin Physics Department and the Physical Sciences Lab were very involved in the design, fabrication and installation of the anti-neutrino detectors for the Daya Bay Experiment.  It was a great opportunity for faculty, staff, and students to participate in an important scientific measurement, while learning about another country and culture.  There were many trips and man years of effort in China by UW physicists, engineers and technicians to construct the experiment and many more for operations and data taking.  This international collaboration took a lot of effort, and in the end produced great results.

The chief experimentalist at UW–Madison was Karsten Heeger who has since left for Yale. At present, Prof. Baha Balantekin is the only one remaining at UW–Madison in the Daya Bay Collaboration.

A completion ceremony will be held Friday, December 11from 7:30-8:3opm CST. Video stream options and the full story can be found at Berkeley Lab’s website.

Researchers awarded Department of Energy Quantum Information Science Grant

Three UW–Madison physics professors and their colleagues have been awarded a U.S. Department of Energy (DOE) High Energy Physics Quantum Information Science award for an interdisciplinary collaboration between theoretical and experimental physicists and experts on quantum algorithms.

The grant, entitled “Detection of dark matter and neutrinos enhanced through quantum information,” will bring a total of $2.3 million directly to UW-Madison. Physics faculty include principal investigator Baha Balantekin as well as Mark Saffman, and Sue Coppersmith. Collaborators on the grant include Kim Palladino at the University of Oxford, Peter Love at Tufts University, and Calvin Johnson at San Diego State University.

With the funding, the researchers plan to use a quantum simulator to calculate the detector response to dark matter particles and neutrinos. The simulator to be used is an array of 121 neutral atom qubits currently being developed by Saffman’s group. Much of the research plan is to understand and mitigate the behavior of the neutral atom array so that high accuracy and precision calculations can be performed. The primary goal of this project is to apply lessons from the quantum information theory in high energy physics, while a secondary goal is to contribute to the development of quantum information theory itself.

Pupa Gilbert elected Fellow of the Mineralogical Society of America

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Proflie photo of Pupa Gilbert

Congrats to Prof. Pupa Gilbert on her election as a Fellow of the Mineralogical Society of America! Members who have contributed significantly to the advancement of mineralogy, crystallography, geochemistry, petrology, or allied sciences and whose scientific contribution utilized mineralogical studies or data, may be designated as Fellows upon proper accreditation by the Committee on Nomination for Fellows and election by the Council. The number of fellows elected each year cannot exceed 0.5% of MSA membership.

Fellows newly elected in 2020 are Jeffrey Catalano, Sylvie Demouchy, Pupa Gilbert, Jun-ichi Kimura, Othmar Muntener, Marc Norman, Alison Pawley, Mark Rivers, Ian Swainson, and Takashi Yoshino.

Full list of MSA Fellows

Mark Friesen promoted to Distinguished Scientist

profile photo of Mark Friesen
profile photo of Mark Friesen
Mark Friesen

Congratulations to Mark Friesen on his promotion to Distinguished Scientist! The distinguished title is the highest title available to an academic staff member at UW–Madison.

Friesen joined the physics department in 2004 as an associate scientist, and has been with UW–Madison since 1998, when he began a postdoc in the Materials Sciences and Engineering department. His main research effort at UW–Madison has been related to silicon quantum dot quantum computing, in collaboration with physics professors Mark Eriksson, Sue Coppersmith, Bob Joynt, Maxim Vavilov, and others.

Friesen says his most important achievement in the department is serving as a research advisor: In 16 years with UW–Madison physics, he has advised or co-advised six postdocs, 11 Ph.D. theses, four current Ph.D. students, two M.S. theses, and several undergraduate research projects. He also has 123 peer-reviewed publications and five U.S. patents, and serves as a consultant for ColdQuanta, a quantum computing company.

“Mark is known around the world for his expertise in semiconductor-based quantum computing,” Mark Eriksson says. “He is especially well known for his calculations on how the band structure in silicon interacts with interfaces to determine the quantum states for electrons in silicon-based quantum devices.”

Congrats, Mark Friesen, on this well-deserved honor!

Welcome, Professor Uwe Bergmann!

profile image of Uwe Bergmann
profile photo of Uwe Bergmann
Uwe Bergmann

From bird feathers that allow for perfectly efficient flight to the bacterial enzyme that fixes nitrogen to help plants grow, nature has had a lot of time to figure things out. “There are so many things we need to be learning how to do from nature, because our methods are still much inferior to those!” says UW–Madison’s newest physics professor, Uwe Bergmann, the Martin L. Perl Professor in Ultrafast X-ray Science. “I think we are going in this direction of learning more and more from nature and using this knowledge to run our world sustainably, but still in a modern way. And that theme brings physicists and many other domains together.”

Bergmann is a physicist who develops and applies x-ray techniques to chemical, biological, engineering, and even archaeological research questions, trying to understand at the atomic level what nature has perfected over a few billion years. Prior to joining the Department on December 1, Bergmann was a Scientist at SLAC. Here, he will focus his research program on continuing to develop and apply novel x-ray techniques. To welcome Bergmann, we sat down for a (virtual) interview.

What is an overview of your research?

My research is developing and applying x-ray methods to solve problems. And these problems can be uncovering hidden writings in ancient books or the chemical elements buried in fossils to reveal the color in the original animal; studying photosynthetic water splitting to understanding the structure of liquid water; and making movies of a molecule carrying out specific work.

What techniques do you use in your research?

I use mainly x-ray techniques, and we do x-ray spectroscopy and sometimes also x-ray scattering and diffraction. The basic difference is that diffraction and scattering looks at the geometric structure — where are the atoms? — and spectroscopy looks at the chemical structure — where are the electrons? Recently we have been using powerful new x-ray lasers, where you can make ultrafast movies showing how chemical bonds are changing in real time. I also use x-ray fluorescence, which is a very powerful imaging technique for creating elemental maps showing the chemical composition of fossils for example.

Once your lab is up and running in Madison, what big projects will you focus on first?

I want to set up a new ultrafast x-UV laser system, able to making these molecular movies with femtosecond resolution. We want to make movies of fast chemical reactions and structural changes; when you expose a material to a light pulse and then watch how the atoms and electrons rearrange after the pulse. This is important for the next generation of advanced materials and a famous example is the water splitting reaction in plants to make O2. We still do not exactly know the mechanism of how these two water molecules are brought in, split up, and forced to make the bond to form O2.

In our latest project with x-ray fluorescence imaging we have scanned more than 50 pages of an ancient parchment book containing the work of the famous Greek physician, Galen of Pergamon. This so-called palimpsest contains a Syriac translation with his work including ‘On Simple Drugs’, which had been erased and overwritten with hymns in the Middle Ages, and catalogued as a new find at Saint Catherine’s Monastery in 1975. Scholars are interested in this translation as it gives information of how Galen’s work originally written in Greek spread east, were it became very popular in the Arab world. Using powerful synchrotron x-rays, we found that you can actually bring out this erased and overwritten text. And scholars can now read it! Key to this success was our new scanning system that records the whole x-ray fluorescence spectrum at each pixel of the image, and our collaborators’ ability to apply advanced machine learning algorithms to enhance the faint traces of overwritten text.

Another exciting project we are working on is an x-ray laser oscillator. There are currently five very big hard x-ray free electron lasers around the world, but they operate in a single pass, which means they are not very stable. Our idea is to use a train of pulses from one of these big x-ray lasers — those are the not-so-clean pulses — to pump our gain medium. After the first pulse creates amplified spontaneous emission, we guide the emitted beam through a cavity made of four mirrors back to the same gain medium to meet up with the next pump pulse from the train. Doing this again and again and again, lets us crank up the beam until we have a perfect, clean and stable x-ray laser pulse, and at the point we will send it out of the cavity. This is similar to how most optical lasers work. We described the idea in PNAS earlier this year, and now we have a lot of work ahead to turn it into reality.

What attracted you to UW–Madison?

For some time, I have been thinking whether it would be possible one day to combine my research activities with teaching at a university. The ultrafast x-ray science chair in the Physics Department was a perfect opportunity and an excellent fit to the research I have been pursuing my entire career. Still, it wasn’t until my visit to Madison, experiencing the wonderful interaction with the students, faculty and staff, and feeling the energy on this beautiful campus, that I fell in love with the idea of joining UW–Madison.

What is your favorite element and/or elementary particle?

Manganese is my favorite element, just because I have been spending so many years studying it and it has so many amazing properties. It’s chemically very important as it has all these different oxidation states, ranging from +2 to +7. And it’s at the heart of the tiny little machine driven by sun light that nature uses to split water into oxygen, which I think is the most important reaction on the planet. Without that reaction there would only be primitive bacterial life on earth. For the elementary particle, I feel almost ashamed but of course it has to be the electron, because it does all the work. Nuclei hardly notice any chemical change, but electrons do all the bonding, all the rearrangements that make the world run; they are the worker bees of nature.

What hobbies/other interests do you have?

I love nature, animals, music, and outdoor activities, especially in and around water.