Precision Measurement

Jun Ye Elected to the American Academy of Arts and Sciences

Steven Burrows — Thu, 23 Apr 2026 04:14:02 +0000

Jun Ye Elected to the American Academy of Arts and Sciences Steven Burrows Wed, 04/22/2026 - 22:14

Steven Burrows / JILA Science Communications Manager

JILA Fellow Jun Ye has been elected a Member of the American Academy of Arts and Sciences, one of the nation’s oldest and most prestigious honorary societies. His election recognizes his extraordinary contributions to physics and quantum science, including pioneering advances in optical atomic clocks, precision measurement, and quantum many-body physics.

Founded in 1780, the American Academy of Arts and Sciences honors excellence across the sciences, humanities, arts, and public affairs, and brings leaders together to address issues of national and global importance. Academy members span centuries of achievement, from early U.S. founders such as John Adams and Benjamin Franklin to generations of influential scientists, scholars, and public leaders. Today, the Academy includes more than 250 Nobel and Pulitzer Prize recipients.

Ye, who is also a professor of physics at the University of Colorado Boulder and a physicist at the National Institute of Standards and Technology (NIST), will be formally welcomed at the Academy’s 2026 Induction Weekend this October in Cambridge, Massachusetts. His election reflects the high regard in which he is held by peers across the physics community and underscores JILA’s enduring leadership in fundamental and applied quantum research.

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Jun Ye Elected Corresponding Member of the Austrian Academy of Sciences

Steven Burrows — Mon, 20 Apr 2026 18:11:48 +0000

Jun Ye Elected Corresponding Member of the Austrian Academy of Sciences Steven Burrows Mon, 04/20/2026 - 12:11

Steven Burrows / JILA Science Communications Manager

JILA Fellow Jun Ye has been elected a corresponding member abroad of the Austrian Academy of Sciences (Österreichische Akademie der Wissenschaften, OeAW), recognizing his internationally influential contributions to physics and quantum science. Election to the OeAW honors scholars whose work has had a profound impact well beyond Austria and reflects exceptional standing within the global research community.

Founded in 1847, the Austrian Academy of Sciences is the country’s leading non-university research institution and a prestigious learned society spanning the natural sciences, humanities, and social sciences. Election as a corresponding member abroad is reserved for distinguished scientists based outside Austria whose research excellence and leadership have shaped their field internationally.

Ye is widely recognized for pioneering advances in optical atomic clocks, precision measurement, and quantum many-body science. His work has set new benchmarks for timekeeping accuracy and has broad implications for fundamental physics, quantum technologies, and geodesy.

As part of the Academy’s 2026 elections, Ye has formally accepted the honor and will be welcomed at official OeAW events in Vienna later this year, including a ceremonial session for newly elected members. His election further highlights JILA’s strong tradition of international scientific leadership and collaboration.

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An Atomic Clock That Stays Cool and Can Rock and Roll Without Losing Time

Steven Burrows — Thu, 09 Apr 2026 15:07:45 +0000

An Atomic Clock That Stays Cool and Can Rock and Roll Without Losing Time Steven Burrows Thu, 04/09/2026 - 09:07

Bailey Bedford / Freelance Science Communicator

A new proposal shows how guiding atoms through a controlled loop of low-energy states using an additional atomic state and a second color of light can eliminate the heating that has long hindered superradiant atomic clocks. The design also makes the laser more robust to vibrations, as coordinated interactions among atoms help keep them synchronized even when the cavity is disturbed.

In popular culture, lasers are often portrayed as portable blasters that superheat whatever they hit. Some lasers do deliver tremendous amounts of energy in reality, but for scientists and engineers, lasers often need to do more than deliver just raw power. They need to deliver a very precise frequency—color—of light.

Precise lasers open many opportunities for experiments and technologies, notably atomic clocks, which offer the most precise timekeeping in the world. Atomic clocks are used in experiments, such as searches for dark matter, and they also make possible everyday technologies, like GPS. Currently, the most precise lasers, and therefore the most precise atomic clocks, are bulky and can be disrupted by small vibrations or changes in temperature, which limits their applications.

In an article published April 9, 2026, in the journal Physical Review Letters, JILA graduate student Jarrod Reilly proposed a new laser design that may allow for greater precision while making lasers more compact and robust. The design was developed along with JILA Fellows Murray Holland and John Cooper, as well as Simon Jäger—who was formerly a JILA postdoctoral researcher and is now an international collaborator at the University of Bonn in Germany. It builds on prior research they and their colleagues at JILA have performed, and their analysis indicated that it solves multiple problems that have limited past experiments. The improvements suggest a way that future atomic clocks can be both more precise and more convenient.

“Time and frequency are the two physical quantities that humans can measure the best,” Holland says. “This high sensitivity allows us to make measurements that are incredibly precise. Pushing it further opens up new domains where we could look farther than we've ever been able to look before.”

The new design is for a type of laser called a superradiant laser, and having a reliable superradiant laser is necessary to create a new type of compact atomic clock called an active atomic clock. Superradiant lasers that could enable active atomic clocks were first proposed by JILA researchers in 2009, and JILA researchers continue to refine the technology. Active atomic clocks use similar principles to standard atomic clocks but include some important tweaks.

Both traditional and active atomic clocks take advantage of the fact that atoms have quantum states which researchers can link together using light. Light comes in quantum packets that each carry a certain amount of energy that corresponds to its frequency—how quickly the light waves oscillate. An atom can be pushed from its initial state into a higher-energy state by hitting it with light of the right frequency. An atom with extra energy will sometimes release light to return to a lower-energy state. The consistent waves of light associated with a particular transition between chosen high- and low-energy atomic states can play a role similar to the steady swinging of a pendulum in a grandfather clock.

Traditional atomic clocks shine a laser on atoms and monitor when the atoms interact with the light at the correct frequency. An active atomic clock, instead, uses many atoms releasing light to create a laser with the desired frequency.

Making an active atomic clock requires getting all the atoms to work together to produce the superradiant laser. If too few atoms emit light at a time, nothing will be observed, and if different atoms simultaneously emit light in the wrong way, the resulting wave that is generated may lose coherence and become unusable.

To coordinate atoms, researchers put them in a special cavity where light bounces between two mirrors. The cavity maintains the frequency of light needed to interact with the atoms and encourages them to synchronize. The process resembles performers coordinating their dance steps by all listening to the same music.

In 2012, Holland collaborated with JILA Fellow James Thompson and demonstrated in experiments that superradiant lasers worked. But there was a hiccup: The process only worked for short periods at a time, and the laser ended up as a series of pulses, which couldn’t be used directly as an active atomic clock. The chamber coordinated the atoms releasing the desired frequency of light. However, when the atoms were put into the chosen energetic state, each atom emitted a small amount of extra light without any coordination. This unpredictable emission resulted in random motion that heated the atoms and eventually disrupted the synchronization needed for superradiance.

The new proposal suggests a method to eliminate the heating. Reilly, who is the first author of the paper, realized the atoms could be guided throughout the entire process and avoid the heating. Reilly observed that utilizing an additional state in the atom allows an experiment to use a different color of light to direct atoms through the troublesome step.

To make it work, he had to select an atom with two very similar states when the atom has as little energy as possible. Researchers can supply light to move the atoms between the two low-energy states. Then, placing the atoms in that additional low-energy state allows a second color of light to be introduced into a cavity that coordinates how the atoms move to the selected energetic state.

Now, the atoms are guided through more than the single dance step of producing the desired frequency. The experiment directs the atoms through a full loop of states, with a scientist controlling where all the energy goes. Each step is carefully managed, and the extra energy is predictably directed away from the atoms, where it can be easily handled.

The group used ideas from particle physics to develop a simulation of the quantum process that Reilly had identified. The simulation showed that the process should eliminate the heating that had previously prevented the creation of active atomic clocks using superradiant lasers.

“This heating rate should be so low that it would be easily manageable in a real apparatus,” Holland says.

But they went beyond eliminating the heating problem. They also discovered that the new design made the laser less sensitive to the shaking of the chamber than prior methods. The atoms didn’t just interact with the light in the cavity but with each other, like performers who can hear each other singing to the music. The new controlled transitions and extra light bouncing back and forth in the cavity should help the atoms interact and remain coordinated. If the cavity is slightly disrupted, it is like the music temporarily cutting out or being distorted, but the singing helps keep the performers coordinated nonetheless.

With increased coordination, the atoms should depend largely on synchronization with each other and less on the cavity, so shaking the cavity shouldn’t have much effect. The researchers used the simulation to show that there are certain ways to set up the experiment in which the frequency of the laser is not sensitive to vibrations of the cavity’s mirrors at all.

“What they're measuring in a clock is that frequency,” Reilly says. “The big-game-changer is that it becomes completely insensitive to vibrations, which people have spent 20 years trying to overcome. You could jump up and down next to the experiment, and in a regular clock, you'd see the color change, but you can jump up and down next to our clock and not see the color change. It should stay stable.”

The researchers also used their simulations to show that even when individual atoms fall out of sync with the others, it shouldn’t disrupt the superradiance—a known problem with some previous methods.

The team says they hope to see the proposal realized in an experiment, and they also want to combine their idea with another concept for the next generation of clocks: nuclear clocks. Nuclear clocks are similar to atomic clocks but use the quantum states of nuclei. The researchers believe their new superradiance technique could solve a lingering issue with nuclear clocks and provide a path to a new generation of unprecedentedly accurate timepieces.

Researchers at JILA propose a new superradiant laser design for next-generation “active” atomic clocks that eliminates atom-heating and vibration sensitivity, two major obstacles that have limited precision and practicality. By carefully guiding atoms through a controlled loop of quantum states, the approach could enable compact, robust atomic—and potentially nuclear—clocks that maintain extreme accuracy even under physical disturbances.

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JILA Graduate Student Anya Grafov Selected as Global Recipient of 2026 Zonta International Women in STEM Award

Steven Burrows — Mon, 06 Apr 2026 16:05:38 +0000

JILA Graduate Student Anya Grafov Selected as Global Recipient of 2026 Zonta International Women in STEM Award Steven Burrows Mon, 04/06/2026 - 10:05

Steven Burrows / JILA Science Communications Manager

Anya Grafov, a graduate student in the Kapteyn‑Murnane Group at JILA, has been selected as one of the global recipients of the 2026 Zonta International Women in STEM Award, an international honor that recognizes exceptional early‑career women for their achievements and leadership in science, technology, engineering, and mathematics. Grafov was nominated through the Zonta Foothills Club of Boulder County and is one of 16 awardees selected worldwide.

“I am incredibly honored to share that I have been selected as one of the global recipients of the 2026 Zonta International Women in STEM Award,” Grafov said. “This recognition is a major milestone in my journey as a physicist.”

The Zonta Women in STEM Award celebrates women between the ages of 18 and 35 whose work demonstrates innovation, technical excellence, and meaningful contributions to advancing knowledge in STEM fields. International awardees each receive a $10,000 award and a complimentary one‑year supporting membership in Zonta International, reflecting Zonta’s mission to inspire future generations and foster inclusivity and diversity in STEM.

The award comes as Grafov enters the final stages of writing her doctoral thesis in ultrafast magnetism. She emphasized that the recognition extends beyond research alone. “More importantly, it reinforces my dedication to amplifying underrepresented voices and building spaces where every student can feel like they truly belong,” she said.

Reflecting on her experiences in physics, Grafov highlighted the importance of supportive research environments. “Having often navigated the isolation of being one of the only women in a male‑dominated field, I understand firsthand the importance of building inclusive communities,” she said.

Grafov expressed gratitude to Zonta International, the Zonta Foothills Club of Boulder County, and Zonta District 12, as well as to her mentors. “I am so proud to represent the physics community and look forward to connecting with the other recipients to create a more equitable future in STEM,” she said.

JILA graduate student Anya Grafov, a member of the Kapteyn‑Murnane Group, has been selected as one of just 16 global recipients of the 2026 Zonta International Women in STEM Award, which recognizes exceptional early‑career women advancing research and innovation in STEM fields worldwide. The award honors Grafov’s work in ultrafast magnetism and her commitment to fostering more inclusive and equitable scientific communities.

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New proposal for using quantum error correction in metrology

Steven Burrows — Sun, 22 Mar 2026 18:16:31 +0000

New proposal for using quantum error correction in metrology Steven Burrows Sun, 03/22/2026 - 12:16

In quantum metrology, it has been considered for some time whether quantum error correction can be used to enhance precision measurements. Here, the primary challenge is devising codes ad protocols that correct noise while not correcting the unknown signal being sensed. In this collaboration with the Pichler, we identify some promising conditions for leveraging quantum error correction for enhanced sensing, even when signal and noise couple identically to sensor qubits.

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Micromechanical membranes can be quiet frequency sensors even at high amplitude

Cindy Regal — Sat, 21 Mar 2026 18:09:09 +0000

Micromechanical membranes can be quiet frequency sensors even at high amplitude Cindy Regal Sat, 03/21/2026 - 12:09

In our work published in NanoLetters, we develop an experimentally straightforward method to evade this tradeoff. Using a patterned, trampoline-shaped membrane, we find that dual-mechanical-mode operation can bring these sensors to a thermally-limited frequency stability. By measuring and correcting for frequency noise arising at high amplitude, we maintain this high stability when operating beyond the linear regime, opening new opportunities for membrane frequency sensing.

Drum-like membrane resonators are intriguing for precision sensing because their resonance frequencies can be sensitive to a variety of parameters of interest, from mass to thermal radiation. The quest for improved sensitivity in tensioned membranes faces a tradeoff in which a high amplitude of mechanical motion improves signal-to-noise, but too high of a drive (beyond the so-called critical amplitude) introduces nonlinear effects.

In our work published in NanoLetters, we develop an experimentally straightforward method to evade this tradeoff. Using a patterned, trampoline-shaped membrane, we find that dual-mechanical-mode operation can bring these sensors to a thermally-limited frequency stability. By measuring and correcting for frequency noise arising at high amplitude, we maintain this high stability when operating beyond the linear regime, opening new opportunities for membrane frequency sensing.

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New 'vacuum ultraviolet' laser may improve nanotechnology, power nuclear clocks

Steven Burrows — Mon, 16 Mar 2026 17:52:31 +0000

New 'vacuum ultraviolet' laser may improve nanotechnology, power nuclear clocks Steven Burrows Mon, 03/16/2026 - 11:52

Daniel Strain / ��Ҵ�ý�ƽ�� Strategic Communications

Physicists at ��Ҵ�ý�ƽ�� have demonstrated a new kind of vacuum ultraviolet laser that could one day allow scientists to observe phenomena currently out of reach for the most powerful microscopes.

The new laser could allow researchers to follow fuel molecules in real time as they undergo combustion, spot incredibly small defects in nanoelectronics, track time with unprecedented precision and more.

The JILA team will present its preliminary findings on March 17 and March 19 at the American Physical Society Global Physics Summit in Denver.

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Breaking The Laser Stability Record Using New Crystalline Mirrors

Steven Burrows — Wed, 18 Feb 2026 15:25:03 +0000

Breaking The Laser Stability Record Using New Crystalline Mirrors Steven Burrows Wed, 02/18/2026 - 08:25

Bailey Bedford / Freelance Science Communicator

A Crystalline Coated 6cm Silicon Cavity. Image credit: Steven Burrows / JILA

In a mirror maze, finding yourself between two mirrors is designed to leave you disoriented and feeling a little unstable. In contrast, getting caught between two mirrors can be incredibly stabilizing for laser light. Scientists make lasers with incredibly stable frequencies by using optical cavities, which are mirrored chambers where light bounces back and forth hundreds of thousands of times.

Researchers at JILA have a long history of improving laser technologies and working with optical cavities. While pushing the limits of laser stability and precision, they have found a plethora of potential disturbances that they have to address to maintain stable frequencies. A tiny vibration, such as from a shaking pump in the lab, can negatively impact the operation of an optical cavity if unchecked.

A team of researchers, led by JILA and National Institute of Standards and Technology Fellow and University of Colorado Boulder Physics professor Jun Ye, has been pushing the limits of stable laser technology for more than two decades, and the team has seen signs that the natural motion of atoms that make up the mirror coatings limit their performance. Overcoming this effect and improving the stability of lasers could unlock new opportunities for experiments, like gravitational wave detectors, and improved technologies, like better atomic clocks.

So, the researchers sought an improved mirror coating. In recent experiments, Ye and his group have collaborated with a team led by Thomas Legero and Uwe Sterr at the Physikalisch-Technische Bundesanstalt in Germany; together, the researchers have tested a new style of crystalline mirror coating expected to mitigate the negative impact of the ways atoms collectively move in the mirror’s structure. In an article published in the journal Physical Review Letters on Jan. 20, 2026, they described the experiment and the unparalleled stability the new coatings allowed them to achieve.

“So far, it had never been demonstrated that these coatings can support superior performance at the state-of-the-art level,” says Dahyeon Lee, a JILA postdoctoral researcher and first author of the article. “This work actually shows that these crystalline coatings give you four times better performance than traditional mirror coatings, while at the same time demonstrating the lowest instability of all optical cavities.”

Optical cavities are so useful in making precision lasers because light wants to naturally fall into certain frequencies when it is trapped between two reflective walls. A particular distance between two mirrors will support certain frequencies while discouraging others. But any vibration of the mirrors or any stretching or contracting of the chamber can interfere with the process and prevent the light from settling precisely into a specific frequency.

Members of Ye’s lab have long ago addressed the most obvious disruptions—like the vibrations of the cooling system that is necessary to keep the cavity working optimally. By using excellent equipment and being vigilant about tamping down vibrations, they have reached a point where things normally run so smoothly that they can see signs of their performance being impaired by the collective motion of all the atoms making up the mirror coating used in the cavity. Inside any solid object, atoms aren’t perfectly still, but depending on the structure of the material, they can all coordinate their motion in particular ways. Certain disturbances of a laser can be dealt with just by averaging the laser’s frequency for a certain amount of time, but the collective movement of the atoms in the mirrors couldn’t be dealt with so easily.

“This is a very special experiment where you can think about both engineering and physics,” says Zoey Hu, a JILA graduate student and author of the article. “What we're really doing here sounds like a simple thing—you're just keeping two mirrors as stable as possible with respect to each other. But when it comes to doing just that one simple thing, there are actually so many little details you have to think about and address.”

To address the collective atomic motion, one of the details the team has considered is how atoms behave in different materials. The new crystalline mirror coatings are made of aluminum, gallium and arsenic and have a structure that keeps the atoms locked more tightly in place than the atoms in the established coatings, which are made from silicon dioxide and tantalum pentoxide and have a more amorphous structure. The strict crystalline structure of the new coatings means the atom’s collective motion experiences less natural loss of energy and fewer random fluctuations in their motion, which should improve the stability of the frequency in experiments.

To show that the coatings were competitive with existing state-of-the-art technologies, the group had to put in some work, including installing the mirror coatings in a high-quality silicon cavity, cooling the cavity down to its frigid optimal temperature (17 K) and ensuring that the system operated smoothly. All their efforts paid off, and the system delivered a more stable frequency than the established coatings could. The coatings require some additional effort to work with, but the results show that the effort can deliver increased stability when the need arises.

“With this technology, and because we already have some other nice cavities, we can show better performance than you could get from any other laser in the world,” says Ben Lewis, a JILA postdoctoral researcher and author of the article. “The crystalline coatings are harder to work with. They're more finicky. But if you want to push and get better performance, they're one of the ways that you can.”

Lewis went on to say that the frequency is tied to the average distance the light travels between reflections and that the stability of their laser frequency averaged over a period of 10 seconds translates into knowing the length of the light’s journey to less than 1 percent of the width of a proton.

Since the coatings produced such great results, the group combined them with another technique that is known to be useful in increasing the stability of a laser frequency when another laser at the same frequency is available. They performed a process, called optical frequency averaging, where two cavities are simultaneously used and the frequency is averaged together. The other cavity used conventional coatings, but its length is more than three times longer, which is an alternative approach to increasing a cavity’s frequency stability. They demonstrated that the technique could increase the resulting frequency stability even further.

The group also shared data they collected that showed how the frequencies of four cryogenic silicon cavities have slowly changed over time. These cavities, located at either JILA or PTB, achieve the best performance currently possible for stable lasers. The frequency observed for each cavity naturally drifts after it is assembled, but over time, the drifting slows down. The data showed the changes of two cavities with the new mirror coatings and two with the established coatings. The exact role the coatings play in producing the drift remains a mystery, but the new data provides clues and indicates that the cavities with new coatings stabilized more quickly than the more established coatings.

While the group has already set a new record for laser frequency stability with the setup, the team is optimistic that the approaches used in these experiments will deliver even better results in the future. They are continuing to observe the cavity with the new coatings to see how it behaves in the long run and to use the cavity in new experiments, including applying it to keeping time.

“We know these cavities are stable and may be much better than the traditional way of doing timekeeping,” Lee says. “We're trying to reimagine how timekeeping can be done in the future by using these silicon cavities as a stable ticking machine.”

JILA researchers, working with collaborators in Germany, demonstrated that new crystalline mirror coatings dramatically reduce atomic-level noise in optical cavities, enabling lasers with record‑breaking frequency stability. By outperforming traditional coatings by a factor of four, these mirrors open the door to more precise experiments and future advances in technologies such as atomic clocks and gravitational‑wave detection.

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Nuclear Clockwork: Experiments Highlight Reproducibility of Nuclear Transition Frequency

Steven Burrows — Fri, 06 Feb 2026 18:32:10 +0000

Nuclear Clockwork: Experiments Highlight Reproducibility of Nuclear Transition Frequency Steven Burrows Fri, 02/06/2026 - 11:32

Artistic representation of a ²²⁹Th nucleus hosted inside a CaF2 crystal experiencing a local electric field gradient. The ²²⁹Th nuclear electric quadrupole moment interacts with the electric field, leading to split energy levels. Image credit: Steven Burrows / JILA

To be useful, clocks need to be consistent. Imagine two spies who synchronize their watches; they rely on them agreeing days or months later, even if one of them must take a frigid hike through arctic tundra. In many experiments, scientists similarly require that their clock is accurate to a tiny sliver of a second and that it will work the same as their colleague’s clock on the other side of the world.

Currently, when keeping time really counts, scientists and engineers turn to atomic clocks. Atomic clocks use the physics that governs the interactions between electrons and light. They can be so accurate that they could run for tens of billions of years without getting off by a second. These clocks have been used for research, such as experiments studying quantum many-body physics and relativity, and have enabled technologies, including GPS. But scientists are not satisfied. Researchers are exploring the potential of nuclear clocks to use the same principles to deliver even more precise results or to fit into an even smaller device.

JILA has been a leader in atomic clock and nuclear clock research, and in 2024 a team of researchers, led by JILA and National Institute of Standards and Technology Fellow and University of Colorado Boulder Physics professor Jun Ye, reported crucial research where they measured the first high-resolution spectrum of the nuclear transition of thorium and determined the absolute frequency of the transition. Ye and other scientists hope these transitions of thorium nuclei will be the ticking hearts of future nuclear clocks. However, there is still a lot for scientists to learn before nuclear clocks have a chance at becoming the gold standard for precision time keeping. For instance, researchers need to understand how nuclear transitions respond to things like changes in temperature, make sure that nuclear clocks can be made with a shared reproducible frequency and determine if they remain reliable over extended periods of time.

In new experiments, Ye and his colleagues have looked at crystals containing thorium to better understand how they might be used in nuclear clocks, including testing three crystal samples many times over the course of a year to check if their properties unexpectedly fluctuated over that time. In an article published in the journal Nature on January 28, 2026, they described the stability of three crystals observed over the course of multiple months, how the crystals responded to temperature changes, and how the different concentrations of thorium in each crystal affected their properties. The results revealed that the crystals have a promising stability and reproducibility and provided insights into future experiments and how similar crystals might be incorporated into high quality clocks.

“Checking frequency reproducibility, both between different host crystals and over an extended period of time, is the first step towards a systematic evaluation of the performance of the nuclear clock,” says Ye.

The group studied three crystals fabricated by Thorsten Schumm’s lab at the Technical University of Vienna. Each crystal was made of calcium fluoride but with some of the calcium atoms replaced with thorium atoms. The crystals each contained different concentrations of thorium. When the thorium atoms are in their lowest energy quantum state, Ye’s group can observe how they interact with particular frequencies of light to make their nucleus jump to higher energy states. They found that there are five transitions that they can trigger with slightly different frequencies of light. The frequencies of these transitions are critical to using thorium in a nuclear clock.

“It’s critical that Thorsten’s lab has provided three different Thorium-doped crystals, which allowed us to study the line width broadening mechanisms and the level of line center reproducibility,” says Ooi.

These interactions and frequencies follow essentially the same physics as the transitions of atoms used in atomic clocks. However, the states of the nucleus are less sensitive to fluctuations of the electric and magnetic fields around them than the states of atoms. Additionally, the nuclear states can be used even when the atoms are embedded in a crystal, unlike the states used for atomic clocks; this difference allows a nuclear clock using a crystal to have a clearer signal by using many more of the relevant atoms while perhaps also being packaged in a smaller device.

Ye’s lab previously studied how one of these crystals behaved at three different temperatures. In the new article, they continued to look at that crystal along with two others with lower concentrations of thorium.

The researchers observed that over the course of the year the properties of the first crystal were stable. The two additional crystals demonstrated the same frequency as the first and also delivered reproducible results when repeated measurements were made months apart. The fluctuations the team observed were stable to around a tenth of a trillionth of the frequency of the measured transition and are limited by the experiment’s measurement precision. These results are promising for researchers to be able to use such crystals to fabricate reliable clocks.

“We are able to show that even over the span of almost a year, we can measure the nuclear transition frequency in these crystals over and over again, and they're very consistent,” says Tian Ooi, a graduate student at JILA and first author of the paper.
The team did find some variations in the crystals’ performances based on the concentration of thorium. While the thorium all interacted with light of the same wavelength, how precisely they responded to the specific frequency varied. The state’s transition will sometimes respond to nearby frequencies and the group defines this extended range of interaction frequencies as the “line width” of the transition.

The group found that the line widths were considerably wider than theoretical calculations had predicted and that they depended on the thorium concentration with greater amounts of thorium producing broader line widths. The researchers propose that the broadening of the width may be caused by the substitution of thorium creating a subtle microstrain in the crystal’s structure that influences the nuclear transitions by making the electric field vary unevenly inside the material.

“This was an unexpected surprise,” says Ooi. “People didn’t anticipate how large this microstrain effect would be.”

Further research is needed to explain the effect and determine if it can be eliminated. Minimizing the line width is a critical factor in designing a high-performance nuclear clock, but high concentrations will also help researchers get a clear signal. So, researchers need to understand this relationship and, if possible, produce crystals with narrower line widths.

The group also continued their research into how the nuclear transition of thorium varied with temperature. They took measurements at more temperatures than they previously had, and for all three crystals, they looked at both the transition that varied the most and the transition that varied least with changes in temperature. The researchers found that the frequencies of the crystals were consistent with each other and identified the point where the material’s changes in response to temperature shift from decreasing the frequency to increasing it, which is where the impact of any temperature fluctuation is smallest. This temperature will likely be the most practical temperature to keep the crystal at when operating a nuclear clock.

The experiments also let the team map out the response of the transition that varies the most with temperature. Based on the results, the researchers suggest that in the future nuclear clocks can monitor that more sensitive frequency to record the temperature so that fluctuations to the least sensitive transition can be rapidly corrected.

Now that the group has these insights, they plan to continue studying these crystals, investigate why the line widths vary between crystals and chart a path to a future with nuclear clocks as a valuable timekeeping tool.

“I think what this paper shows is that we're moving from measuring the clock transition to really investigating how good this clock can be,” Ooi says. “There’s still interesting things to figure out, but this is one of the big steps that we have to take to show that solid-state nuclear clocks are viable.”

_{The authors acknowledge funding support from National Science Foundation QLCI OMA-2016244, DOE quantum center of Quantum System Accelerator, Army Research Office (W911NF2010182), Air Force Office of Scientific Research (FA9550-19-1-0148), National Science Foundation PHY-2317149, and National Institute of Standards and Technology. Part of this work has been funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 856415) and the Austrian Science Fund (FWF) [Grant DOI: 10.55776/F1004, 10.55776/J4834, 10.55776/ PIN9526523]. The project 23FUN03 HIOC [Grant DOI: 10.13039/100019599] has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Program and by the Participating States. We thank the National Isotope Development Center of DoE and Oak Ridge National Laboratory for providing the Th-229 used in this work.}

JILA researchers have taken a major step toward realizing next‑generation nuclear clocks by studying how thorium‑doped crystals behave over time. In new experiments published in Nature, the team tracked the stability, temperature response, and reproducibility of three calcium‑fluoride crystals containing different concentrations of thorium. Over nearly a year of measurements, all three crystals demonstrated remarkably stable nuclear transition frequencies—an essential requirement for building reliable nuclear clocks.

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JILA Collaboration Makes Cavity Quantum Electrodynamics into a Team Sport

Steven Burrows — Thu, 27 Nov 2025 19:01:01 +0000

JILA Collaboration Makes Cavity Quantum Electrodynamics into a Team Sport Steven Burrows Thu, 11/27/2025 - 12:01

Bailey Bedford / Freelance Science Communicator

Researchers used laser light to trigger a rapid sequence where atoms absorb and emit photons, shifting between energy states. Each emitted photon, now a different color, bounces through the cavity and drives the next atom’s transition, enabling a rare three-body interaction. Image Credit: Steven Burrows / JILA

Reality is the result of countless interactions. Everything in daily life, from a grain of dust floating in the air to a neuron firing in a brain, is the result of myriads of atoms and other quantum particles interacting.

Often, we get by with ignoring interactions and seeing just the big picture result. However, physicists learn a lot by digging down to the foundation and studying how the interactions between particles play out. In the past, researchers have mostly simplified things by focusing on interactions between two objects at a time—two-body interactions. However, reality isn’t always so simple. Sometimes three or more particles interact in fundamentally different ways than groups of interacting pairs would.

For the past several years, an experimental research group led by JILA Fellow James Thompson and a theoretical research group led by JILA Fellow Ana Maria Rey have been working together to study quantum interactions using cavity quantum electrodynamics (cavity QED)—the science of how light contained in reflective cavities interacts with quantum particles, like individual atoms. Recently, they tackled many-body interactions with a new experiment, described in an article published in the journal Science. In the experiment, they successfully created interactions that require the participation of either three or four atoms to achieve the observed results.

“Nature’s forces act between pairs, but when many particles come together, new interactions can emerge,” says Rey, who is also a National Institute of Standards and Technology (NIST) Fellow and a University of Colorado Boulder Physics professor. “Controlling these multi-body interactions opens the door to faster, richer and more powerful quantum matter.”

The new experiment took their research from looking at situations where all interactions are essentially the result of atoms playing two-player sports to a more complex world where atoms participate in team sports. Instead of two tennis players hitting a ball back and forth, the experiment introduces a baseball team where the ball gets thrown between several players. The change expands their ability to form quantum connections between the players.

“This is a whole new path to generate quantumy-stuff called entanglement that will improve quantum sensors for navigation, atomic clocks and maybe even detect exotic things like dark matter or gravitational waves,” says Thompson, who is also a NIST physicist and University of Colorado Boulder Physics professor.

The experiment used rubidium atoms as the players, and their games—interactions—were carried out by tossing around light. The researchers used cavities as the playing field and supplied around a thousand atoms to form small teams. The researchers controlled the colors of light they sent into the cavity and how different colors of light behaved in the cavity, which helped them set the rules of the game.

The researchers focused on the quantum states of the atoms defined by the movement of the atoms through the chamber. Thanks to conservation laws, the atoms couldn’t just change their speeds and run around the experiment in any random way; to change states, they needed to receive or release exactly the right amount of energy and momentum. The researchers set up the experiment so the only way the atoms could change states was by catching or releasing photons—individual particles of light that carry specific amounts of energy and momentum.

Since the atoms were in a frictionless vacuum, they didn’t stay in place like a pitcher on the mound when they caught or threw a photon. Instead, it was like the atoms were a baseball team forced to play on ice or were astronauts playing the game of catch while floating in the middle of a spacewalk: Every catch and throw gave them a shove.

The quantum nature of the atoms meant they were only stable in certain specific states, and each atom could only catch a photon if there was an appropriate state for it to move into afterward. This allowed the researchers to carefully design interactions by choosing what colors of light were in the cavity.

They focused on moving atoms between two stable states, and they made sure the cavity didn’t contain light that could simply knock an atom between the states with a single caught photon (the resulting interactions would be boring). Instead, they created a playing field where atoms had to coordinate a specific play—string of interactions—to move between stable states. They ensured that each game started and ended with photons whose energy differed by exactly enough to move three atoms between states.

To start the play, the researchers flooded the cavity with light that could push the atoms to an energetic state that they couldn’t stay in for long. Each time an atom caught a photon, it immediately threw out a photon to return to a lower energy state. Sometimes it threw out a photon just like the one it caught and returned to its original state. Other times, it instead tossed out a weaker photon and kept a little bit of its new energy and momentum. The only allowed option was keeping exactly enough to settle into the second stable state.

This released photon was a new color and was free to bounce around the cavity and quickly be caught by another atom. Similar to the first step, catching the light temporarily shoved the second atom to an unstable state before it, in turn, tossed off another photon. Again, the second atom sometimes kept enough energy and momentum to join the first atom in the new state. The process continued with a third atom joining the first two by catching the new photon and throwing out another weakened photon.

To ensure the chain of events, the researchers set up their cavity to encourage the presence of the initial light and the final photons released in this game of catch while being inhospitable to other undesired colors of light. The dynamics of the light in the cavity and the rubidium atoms’ available quantum states meant the whole play had to happen quickly or not at all.

“We build very strict rules in our system that all three processes have to happen at the same time in order for momentum and energy to be conserved,” says Chengyi Luo, the co-lead author of the paper.

The researchers confirmed the atoms moved between states following the prescribed three-body interactions, and they went a step further. They illustrated the adaptability of the approach by increasing the amount of energy and momentum available to fuel four-body interactions, adding another player to each game of catch. Their observations showed the atoms teaming up into a smoothly running machine and moving in groups of four to the new state.

These demonstrations are just the first steps in exploring many-body interactions with this approach.

“There are a lot of things people need to figure out about how we're going to explore these multibody interactions to make them useful,” Rey, says. “We just saw them, but there are a lot of new behaviors and capabilities to be explored. For example, we think they can be used to emulate exotic superconductors where four electrons team up instead of two electrons like in normal superconductor, producing a new kind of supercurrent that may contribute to high temperature superconductors.”

In the future, experiments should be able to use different quantum states, induce interactions between even larger numbers of particles and make the interactions do practical work. The ability to involve more particles in each interaction provides a new set of tools for researchers. As the technique is explored and refined, it has potential applications in a variety of areas including quantum simulation, quantum computing and quantum sensing.

“I think it's interesting that there's this new way to change the quality of the communication that can happen between all these atoms,” Thompson says. “You really fundamentally change what that communication looks like. It's just an open physics question, like, ‘Well, how good can it be?’ and going further ‘Can we build new quantum states to simulate and explore the universe around us?’”

For the past several years, an experimental research group led by JILA Fellow James Thompson and a theoretical research group led by JILA Fellow Ana Maria Rey have been working together to study quantum interactions using cavity quantum electrodynamics (cavity QED)—the science of how light contained in reflective cavities interacts with quantum particles, like individual atoms. Recently, they tackled many-body interactions with a new experiment, described in an article published in the journal Science. In the experiment, they successfully created interactions that require the participation of either three or four atoms to achieve the observed results.

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