The Royal Swedish Academy of Sciences on Tuesday awarded the 2025 jointly to , and , “for the discovery of macroscopic quantum mechanical tunneling and energy quantization in an electric circuit.”

Clarke, a professor emeritus of physics at the University of California, Berkeley, collaborates with the at the 91̽��. ADMX scans for evidence of dark matter from beneath the Seattle campus, in a cold dark box surrounded by a powerful magnetic field. The experiment is managed by the U.S. Department of Energy’s and it hinges on technology designed by Clarke.

“I was elated upon hearing the news about John. Simply elated,” said , a 91̽��professor emeritus of physics and lead scientist at ADMX.

The three laureates were recognized for that captured two quantum mechanical properties at the visible scale. Clarke’s brainchild, which caught Rosenberg’s attention 25 years ago, is a Superconducting Quantum Interference Device, or SQUID, which can make ultrasensitive measurements.

“John Clarke first got involved with ADMX around 2000,” Rosenberg recalled. “To this day, he remains a much-loved ADMX collaborator.”

The relationship began when ADMX organized a workshop at Lawrence Berkeley Laboratory to brainstorm solutions to a technical issue the researchers had encountered. The way the experiment searches for dark matter is akin to a radio searching for a station, but instead of music, it is looking for axions — the particles theorized to make up dark matter.

Detecting axions requires amplifying very, very quiet microwaves. At the time, the group only had access to noisy electronic amplifiers, which were drowning out the very signal they sought to capture. At the workshop, Clarke presented a SQUID amplifier as a potential solution.

“We considered all kinds of alternative technologies, but none fit the bill,” Rosenberg said. “The SQUID amplifiers were indeed the breakthrough we needed.”

Clarke joined ADMX and brought the amplifiers with him. , a 91̽��professor of physics and co-spokesperson for ADMX, was a postdoc at the time.

“The SQUID amplifiers gave us the sensitivity necessary to do a search,” Rybka said. “We’ve been operating for years and years and have only explored a fraction of the space, but we couldn’t have even started without these amplifiers.”

ADMX is still using an iteration of Clarke’s original amplifier, improved upon by his students over the years. Still, the “big transition,” was moving to the SQUID amplifier, and that is just one example of how this technology can revolutionize an experiment.

“The laureates moved the field of particle physics from classical measurement to quantum sensing,” Rybka said. “It makes stuff that used to just be on the blackboard — quantum mechanics — experimentally accessible and even useful. In my opinion, you wouldn’t have modern quantum computers without the work done by this group.”

The humble neutrino, an elusive subatomic particle that passes effortlessly through normal matter, plays an outsized role among the particles that comprise our universe. To fully explain how our universe came to be, scientists need to know its mass.

But, as it turns out, the neutrino avoids being weighed.

In a published Sept. 6 in Physical Review Letters, an international team of researchers in the United States, Germany and France reported that a distinctive strategy they have used shows real promise to be the first approach to measure the mass of the neutrino. Once fully scaled up, their collaboration — — could also reveal how neutrinos influenced the early evolution of the universe as we know it.

“Project 8 is an entirely new approach to trying to solve this outstanding, fundamental problem in physics — the mass of the neutrino — and we really think it is on course to answer this question and so much more,” said co-author and Project 8 scientist , a 91̽�� assistant professor of physics.

In 2022, , a separate collaboration based in Germany, set a new upper limit for the neutrino’s mass — a decades-long endeavor that 91̽��researchers helped lead. But KATRIN is eventually expected to reach the limits of how much it can narrow the range of the neutrino’s mass, leaving scientists around the world asking, “What’s next?”

Project 8 scientists believe their approach might be the answer. Their work focuses on a well-characterized phenomenon called beta decay. Many radioactive variants of elements undergo this process. Project 8 hinges on using the beta decay of tritium — a rare, radioactive variant of hydrogen — to calculate the mass of the neutrino.

When tritium undergoes beta decay, it generates a helium ion, an electron and a neutrino. Rather than try to detect the neutrino, which passes through most detector technology, the research team has instead focused on measuring the free electron generated during beta decay. These electrons carry away most — but not all — of the energy released by beta decay. And that “missing” energy is made up of the neutrino’s mass and motion.

“The neutrino is incredibly light,” said co-author Talia Weiss, a Project 8 scientist and graduate student at Yale University. “It’s more than 500,000 times lighter than an electron. So, when neutrinos and electrons are created at the same time, the neutrino mass has only a tiny effect on the electron’s motion. We want to see that small effect. So, we need a super-precise method to measure how fast the electrons are zipping around.”

In their recent paper, Project 8 scientists showed that they can use a new technique — cyclotron radiation emission spectroscopy, or CRES — to reliably track and record beta decay. According to their results, CRES could be used to calculate neutrino properties, including its mass.

“In principle, with technology developments and scale up, we have a realistic shot at getting into the range necessary to pin down the neutrino mass,” said co-author Brent VanDevender, a Project 8 scientist at the , a U.S. Department of Energy facility.

Physicists Joe Formaggio and Ben Monreal first conceived of CRES more than a decade ago at the Massachusetts Institute of Technology. An international team rallied around the idea and formed Project 8 to convert their vision into a practical tool. CRES captures the microwave radiation emitted from newborn electrons as they spiral around in a magnetic field.

Project 8 scientists spent years figuring out how to accurately tease out the electron signals from background noise. Weiss and Christine Claessens — a 91̽��postdoctoral researcher who worked on Project 8 as a doctoral student at the University of Mainz in Germany — performed the two final analyses that placed limits on the neutrino mass using CRES data. This is the first time that tritium beta decays have been measured, and an upper limit placed on the neutrino mass, with the CRES technique.

The CRES detector, built and housed at the UW, measures that crucial electron energy with the potential to scale up beyond any existing technology. Novitski said that scalability is what sets Project 8 apart.

“Nobody else is doing this,” Novitski said. “We’re not taking an existing technique and trying to tweak it a little bit. We’re kind of in the Wild West.”

In their most recent experiment, the team tracked 3,770 tritium beta decay events over an 82-day trial window in a sample cell the size of a pea. The sample cell is cryogenically cooled and placed in a magnetic field that traps the emerging electrons long enough for the system’s recording antennas to register a microwave signal.

A subset of Project 8 researchers have also developed a suite of specialized software — each named after insects, like Katydid and Dragonfly — to convert raw data into signals that can be analyzed. And project engineers have had to design and build the hardware and detectors that make Project 8 come together.

“We do have engineers who are crucial to the effort,” Novitski said. “It’s kind of out there from an engineer’s point of view. Experimental physics is at the boundary of physics and engineering. You have to get particularly adventurous engineers and practical-minded physicists to collaborate, to make these things come into being, because this stuff is not in the textbooks.”

Now that the team has shown their experimental system works using molecules of tritium, they’re working on designs for scaling up the experiment from the pea-size sample chamber to one a thousand times larger to capture more beta decay events. They’re also developing an experimental set-up to produce, cool and trap individual atoms of tritium — no easy feat since tritium, like its more abundant cousin hydrogen, prefers to bind to other atoms and form molecules.

Meeting these goals, and scaling up the whole apparatus, will be the critical steps to reaching and ultimately exceeding the sensitivity achieved by the KATRIN experiment.

“This will be a years-long effort. But one that we think will finally give us this small answer — the mass of this tiny neutrino — with huge implications,” said co-author and Project 8 scientist , a 91̽��professor of physics.

Other 91̽��co-authors include current and former graduate students Ali Ashtari Esfahani, Jeremy Hartse and Eris Machado; , emeritus research professor of physics; and , professor emeritus of physics. Project 8 is funded by the U.S. Department of Energy, the National Science Foundation, the German Research Foundation and internal investments by collaborating institutions.

For more information, contact Novitski at en37@uw.edu.

Adapted from a by the Pacific Northwest National Laboratory.

Forty years ago, scientists theorized a new kind of low-mass particle that could solve one of the enduring mysteries of nature: what dark matter is made of. Now a new chapter in the search for that particle has begun.

This week, the (ADMX) unveiled a new result, in the journal , that places it in a category of one: it is the world’s first and only experiment to have achieved the necessary sensitivity to “hear” the telltale signs of dark matter axions. This technological breakthrough is the result of more than 30 years of research and development, with the latest piece of the puzzle coming in the form of a quantum-enabled device that allows ADMX to listen for axions more closely than any experiment ever built.

ADMX is based at the 91̽�� and managed by the U.S. Department of Energy’s . This new result, the first from the second-generation run of ADMX, sets limits on a small range of frequencies where axions may be hiding, and sets the stage for a wider search in the coming years.

“This result signals the start of the true hunt for axions,” said Fermilab’s Andrew Sonnenschein, the operations manager for ADMX. “If dark matter axions exist within the frequency band we will be probing for the next few years, then it’s only a matter of time before we find them.”

One theory suggests that the dark matter that holds galaxies together might be made up of a vast number of low-mass particles, which are almost invisible to detection as they stream through the cosmos. Efforts in the 1980s to find this particle, named the axion by theorist Frank Wilczek, currently of the Massachusetts Institute of Technology, were unsuccessful, showing that their detection would be extremely challenging.

ADMX is an axion haloscope — essentially a large, low-noise, radio receiver, which scientists tune to different frequencies and listen to find the axion signal frequency. Axions almost never interact with matter, but with the aid of a strong magnetic field and a cold, dark, properly tuned, reflective box, ADMX can “hear” photons created when axions convert into electromagnetic waves inside the detector.

“If you think of an AM radio, it’s exactly like that,” said , co-spokesperson for ADMX and assistant professor of physics at the 91̽��. “We’ve built a radio that looks for a radio station, but we don’t know its frequency. We turn the knob slowly while listening. Ideally we will hear a tone when the frequency is right.”

This detection method, which might make the “invisible axion” visible, was invented by Pierre Sikivie of the University of Florida in 1983, as was the notion that galactic halos could be made of axions. Pioneering experiments and analyses by a collaboration of Fermilab, the University of Rochester and the U.S. Department of Energy’s Brookhaven National Laboratory, as well as scientists at the University of Florida, demonstrated the practicality of the experiment. This led to the construction in the late 1990s of a large-scale detector at the U.S. Department of Energy’s Lawrence Livermore National Laboratory that is the basis of the current ADMX.

It was only recently, however, that the ADMX team has been able to deploy superconducting quantum amplifiers to their full potential enabling the experiment to reach unprecedented sensitivity. Previous runs of ADMX were stymied by background noise generated by thermal radiation and the machine’s own electronics.

Fixing thermal radiation noise is easy: a refrigeration system cools the detector down to 0.1 Kelvin (roughly -460 degrees Fahrenheit). But eliminating the noise from electronics proved more difficult. The first runs of ADMX used standard transistor amplifiers. Then, the researchers connected with John Clarke, a professor at the University of California Berkeley, who developed a quantum-limited amplifier for the experiment. This much quieter technology, combined with the refrigeration unit, reduces the noise by a significant enough level that the signal, should ADMX discover one, will come through loud and clear.

“The initial versions of this experiment, with transistor-based amplifiers would have taken hundreds of years to scan the most likely range of axion masses. With the new superconducting detectors we can search the same range on timescales of only a few years,” said Gianpaolo Carosi, co-spokesperson for ADMX and scientist at Lawrence Livermore National Laboratory.

“This result plants a flag,” said , professor of physics at the 91̽�� and chief scientist for ADMX. “It tells the world that we have the sensitivity, and have a very good shot at finding the axion. No new technology is needed. We don’t need a miracle anymore, we just need the time.”

ADMX will now test millions of frequencies at this level of sensitivity. If axions are found, it would be a major discovery that could explain not only dark matter, but other lingering mysteries of the universe. If ADMX does not find axions, that may force theorists to devise new solutions to those riddles.

“A discovery could come at any time over the next few years,” said scientist Aaron Chou of Fermilab. “It’s been a long road getting to this point, but we’re about to begin the most exciting time in this ongoing search for axions.”

The ADMX collaboration includes scientists at Fermilab, the 91̽��, Lawrence Livermore National Laboratory, Pacific Northwest National Laboratory, Los Alamos National Laboratory, the National Radio Astronomy Observatory, the University of California at Berkeley, the University of Chicago, the University of Florida and the University of Sheffield. This research is supported by the U.S. Department of Energy Office of Science, the Heising-Simons Foundation and research and development programs at the U.S. DOE’s Lawrence Livermore National Laboratory and the U.S. DOE’s Pacific Northwest National Laboratory.

###

For more information, contact Sonnenschein at 630-840-2883 or sonnenschein@fnal.gov and Rybka at 206-543-2797 or grybka@uw.edu.

This is a joint  by Fermilab and the 91̽��.

A paper published this month in shows that 91̽��researchers and collaborators have managed to detect the radiation flung off by a single electron, a key step in their new strategy to pin down the neutrino’s mass.

The ultimate goal is to measure the weight of the neutrino. Scientists used to think the subatomic particle had no mass, but results starting in 1998 turned that idea on its head.

“Neutrino mass not being zero is the only definitive example where a prediction of the standard model of particle physics has been contradicted by data,” said co-author , a 91̽��professor of physics.

The 91̽��scientists are part of , a group of six institutions that seeks to measure the mass of the neutrino. Collaborators on the new study are at the Massachusetts Institute of Technology; the Pacific Northwest National Laboratory; the University of California, Santa Barbara; the National Radio Astronomy Observatory in Virginia; and the Karlsruhe Institute of Technology in Germany.

The new paper shows they were able to track electrons from radioactive decay inside an apparatus on the 91̽��campus for several milliseconds, long enough to make a rough measurement of a single electron’s energy without disturbing it. Next will be relating that electron’s energy to the neutrino’s mass.

“We want to know the mass of the neutrino because we want to understand how the enormous skeins and clusters of galaxies formed from the uniform early universe,” Robertson said.

Measuring the neutrino’s mass could also help explain the physics of very-high-energy reactions and help develop a new of particle physics, he added.

The core of the apparatus, located in the UW’s physics building, is a low-pressure gas cell about the size of an espresso cup inside a strong 1-tesla magnet. The cell contains a small amount of metastable krypton-83 gas, a radioactive isotope that spews out electrons as its nucleus undergoes radioactive decay. These ejected electrons are then forced into a circular orbit by the magnetic field and emit cyclotron radiation, the electromagnetic waves emitted by charged particles as they move through a magnetic field. A detector measures the waves’ frequency, around 25 billion cycles per second, to gauge the electron’s energy.

Neutrinos also are created in . Their existence, first predicted by theoretical physicist Wolfgang Pauli in 1930, is needed to ensure that beta decay conserves energy and angular momentum. This experiment aims to measure the energies of the electrons emitted in beta decay and compare them to the total energy of the reaction. If the neutrino has mass, the ejected electron cannot have an energy equal to the total amount, since (according to Einstein’s famous equation, E=mc², relating energy and mass) some of this energy must have been used to make the neutrino.

The mass of the unseen neutrino can therefore be measured by carefully tallying the energy of the emitted electron to figure out how much energy is missing.

The current detector only has a resolution of about 15 electron volts, which is too imprecise to measure the neutrino’s mass. The 91̽��team is now working to build a bigger apparatus and better precision for the energy measurements. Robertson believes the ultimate precision could be as low as 0.04 electron volts, much lower than any existing method. But he says it will take years to get there.

The researchers have named the new technique cyclotron radiation emission spectroscopy, or CRES.

“In addition to being a step on the path to measuring the neutrino mass, I’m excited that we’ve made a new tool for measuring radioisotope decay energies in general,” said , a 91̽��research assistant professor of physics. “It is my hope that the CRES technique ends up having even broader applications. We’re exploring both ideas for testing fundamental physics and more practical applications.”

Many of the collaborators on this project met through the , a particle detector in a Canadian mine that collected some of the first measurements to show that the neutrino does have mass.

Rybka is also involved in a 91̽��experiment using microwave radiation to find an , a hypothesized subatomic particle that would be a component of dark matter, a form of matter that cannot be detected but is thought to make up most of the mass of the universe.

Other 91̽��scientists among the 27 authors who contributed to the paper are professor , research professor , research scientists and , doctoral students and , affiliate professor , and former staff member Natasha Woods.

The research was funded by the U.S. Department of Energy, the National Science Foundation and the Pacific Northwest National Laboratory.

###

For more information, contact Robertson at rghr@uw.edu or 206-616-2745 and Rybka at grybka@uw.edu or 206-543-2540. To tour the lab, contact Fertl at mfertl@uw.edu or 206-543-9134.

Parts of this article were adapted from a on the American Physical Society website.