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High School Students Present Science and Engineering Projects at JILA

Steven Burrows — Fri, 24 Apr 2026 15:11:25 +0000

High School Students Present Science and Engineering Projects at JILA Steven Burrows Fri, 04/24/2026 - 09:11

Jessica Hoehn / JILA PFC Director of Public Engagement & Education Research

Eric Cornell talks to a student about their project.

On April 22, 2026, the JILA Physics Frontier Center (PFC) and Partnerships for Informal Science Education in the Community (PISEC) hosted the annual PISEC High School Poster Symposium. 110 students from three different high schools descended on JILA to present posters of science and engineering projects they completed over the course of a semester or year under the guidance of CU mentors. This cornerstone event provides students an opportunity to engage in authentic science communication practices, sharing their work with peers and university researchers. In addition to the poster session, high school students toured research labs in JILA, learning about JILA research and exploring possible future undergraduate opportunities and career paths.

Funded by the National Science Foundation through the JILA PFC, PISEC is a partnership-based community engagement program that connects CU volunteers with local K-12 students to engage in hands-on, inquiry-based science experiments and engineering projects. With programs at the elementary through high school levels, PISEC strives to cultivate youths’ interest in science, technology, engineering, and math (STEM) and support their STEM identity development. Through mutually beneficial partnerships, the program works to create pathways into STEM disciplines while also supporting the identity and professional development of the university volunteers.

This year, students from Englewood, Northglenn, and Skyline High Schools presented a wide range of projects, from investigating aurora phenomena with a homopolar motor, to creating 3D printed bone scaffolds for tissue engineering, to designing a pedestrian bridge. JILA graduate students, postdocs, and fellows attended the poster session, along with other CU and external community members, making for a lively atmosphere of celebration and connection.

On the heels of PISEC’s 18th year of building and sustaining university-community partnerships, this vibrant symposium underscores JILA’s commitment to community engagement and to supporting the next generation of scientists.

High school students explain their project to poster symposium attendees.

More than 110 students from three Colorado high schools gathered at JILA on April 22, 2026, to present science and engineering projects at the annual PISEC High School Poster Symposium, hosted by the JILA Physics Frontier Center and PISEC. The event offered students hands-on experience in science communication, opportunities to engage with CU researchers, and a firsthand look at JILA research and STEM pathways.

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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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Google Quantum AI Engages JILA Fellow Adam Kaufman to Lead New Neutral Atom Quantum Computing Effort

Steven Burrows — Tue, 24 Mar 2026 19:12:02 +0000

Google Quantum AI Engages JILA Fellow Adam Kaufman to Lead New Neutral Atom Quantum Computing Effort Steven Burrows Tue, 03/24/2026 - 13:12

Steven Burrows / JILA Science Communications Manager

Adam Kaufman (left) inspects an optical atomic clock at JILA on the University of Colorado campus with students Nelson Darkwah Oppong, Alec Cao and Theo Lukin Yelin. (Image Credit: Patrick Campbell, University of Colorado)

Today, Google Quantum AI announced a major expansion of its quantum computing research program, naming JILA Fellow Adam Kaufman to lead a newly formed neutral atom quantum hardware team. The initiative marks Google’s first large-scale investment in neutral atom quantum computing, a rapidly advancing platform that complements its long‑standing work in superconducting qubits.

Kaufman, an internationally recognized leader in neutral atom physics, will continue his research at JILA as a JILA Fellow while maintaining his academic appointment in the Department of Physics at the University of Colorado Boulder. According to The Colorado Sun, Kaufman’s dual role reflects Google’s strategy of closely integrating industrial-scale engineering with cutting-edge academic research, particularly in Boulder’s growing quantum ecosystem.

In announcing the program, Google emphasized that neutral atom quantum processors offer unique advantages, including the ability to scale to very large arrays—currently on the order of thousands to tens of thousands of qubits—with highly flexible, “any‑to‑any” connectivity. While neutral atom systems operate more slowly than superconducting circuits, their scalability in qubit number makes them especially promising for quantum simulation and fault‑tolerant architectures. Google views the parallel development of both platforms as a way to accelerate progress toward commercially useful quantum computers.

This new collaboration further strengthens JILA’s national and international leadership in quantum science, building on its major federally funded research centers and broad portfolio of competitive grants. By bridging foundational research and industrial-scale quantum engineering, the partnership underscores JILA’s central role in shaping the future of quantum technology.

Please join us in congratulating Adam Kaufman on this exciting opportunity and on his continued contributions to JILA, ��Ҵ�ý�ƽ��, and the global quantum research community.

Learn more:

The Colorado Sun: Google taps Boulder physicist to lead new quantum computing effort
Google Quantum AI Blog: Building superconducting and neutral atom quantum computers

Google Quantum AI has named JILA Fellow Adam Kaufman to lead a new neutral atom quantum computing hardware team, marking a major expansion of its quantum research program. Kaufman will continue his research at JILA and ��Ҵ�ý�ƽ��, strengthening JILA’s leadership and impact in national and international quantum science.

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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 Researchers Overturn 25-Year-Old Explanation of Benzene Formation in Space

Steven Burrows — Fri, 09 Jan 2026 18:21:00 +0000

JILA Researchers Overturn 25-Year-Old Explanation of Benzene Formation in Space Steven Burrows Fri, 01/09/2026 - 11:21

Bailey Bedford / Freelance Science Communicator

Interstellar formation of PAHs terminates at C6H5+. Image credit: Steven Burrows / JILA

Space is famously empty. The cold vacuum of space—or more specifically, the interstellar medium—lacks much of anything, including the air needed to conduct sound. But it isn’t quite completely empty. While it’s vacant compared to what we experience in daily life, there are occasional atoms and molecules spread throughout it.

Those atoms and molecules mean that there is chemistry in space, although it doesn’t always resemble the dense, warm reactions that routinely occur in a chemist’s test tubes. One aspect of chemistry in space that researchers are interested in is the formation of polycyclic aromatic hydrocarbons (PAHs), which are molecules of carbon and hydrogen that make a broad array of chemicals on earth and in the void of space. Researchers have seen signs of light interacting with a variety of these molecules in space and being absorbed—leaving a distinctive fingerprint in the remaining light that reaches Earth. These molecules are estimated to contain somewhere between a tenth and a quarter of the carbon spread across the interstellar medium, and the molecules’ foundational building blocks are benzene (C₆H₆)—a ring of six carbon atoms, each holding a hydrogen atom.

Since 1999, researchers have had a model that they thought explained how benzene formed from smaller molecules. However, the challenges of performing experiments at the low temperatures and densities involved in mimicking the conditions in the interstellar medium have meant that researchers have relied on their theoretical understanding of the process and haven’t thoroughly tested it in experiments.

Now, JILA Fellow and University of Colorado Boulder Physics Professor Heather Lewandowski and members of her lab have used tools developed in physics laboratories to recreate the necessary conditions and have investigated how the chemistry plays out. The team described their experiment in an article published in the journal Nature Astronomy in May 2025. When they tested the process, the first steps played out as expected, but then they were surprised to find that the benzene failed to form at the final step. Their results give scientists a new window into how chemistry occurs in the interstellar medium and reopens the question of how carbon gets caught up in PAHs throughout space.

The key to recreating the chemistry occurring in the interstellar medium was creating a vacuum in a chamber and using lasers to cool molecules and hold them in place in the vacated space. This required the researchers to look at just a small number of molecules and to set aside the beakers and test tubes that are stereotypical of chemistry and instead rely on large metal chambers, air pumps, laser beams and many mirrors and lenses.

“It's a laboratory full of lasers, and vacuum chambers, and optics,” Lewandowski says. “It fills up half a room to be able to cool down these hundred little molecules.”

Selecting the right color of laser and aligning the beams correctly allows the researchers to suspend—trap—particles in a vacuum chamber as well as cool them down through a process called laser cooling. Laser cooling relies on the fact that light can give atoms and molecules a shove to slow them down and that the interaction can be tailored to depend on how the particles are moving. Carefully applied, laser cooling can get molecules down to temperatures just above absolute zero.

“Laser cooling and trapping has really been in the domain of physicists,” Lewandowski says. “The nice thing about JILA is we have physicists and chemists working together. In my own group, we have both backgrounds, and so we have the tools now that can answer these questions that really chemists didn't have the technology to tackle and physicists didn't know it was an interesting question to answer.”

These techniques allow them to focus on a small number of molecules and get a close look at the interactions that normally are obscured in a chaos of many reactions occurring rapidly and simultaneously.

With the equipment creating the needed conditions, the group started following the proposed recipe for creating benzene in the interstellar medium. The recipe’s main ingredient is a molecule of two carbon atoms and two hydrogen atoms, called acetylene (C₂H₂). The first step is mixing acetylene with molecules containing two nitrogen atoms and one hydrogen atom (N₂H⁺). The nitrogen atoms can provide their hydrogen atom to create new molecules with two carbon and three hydrogen atoms. That opens the door to two more steps of interactions with acetylene molecules to produce a molecule with six carbon atoms and five hydrogen atoms (C₆H₅⁺)—just one hydrogen short of the target benzene ring. The exact behavior of this molecule is not thoroughly understood, but the established recipe proposed that it could form benzene by capturing a molecule made from a pair of hydrogens and then letting the excess atoms go.

The team supplied just enough of the needed ingredients in the chamber so that it was improbable that more than two molecules would be reacting at a time. Using laser cooling, they cooled the molecules in the chamber down to just a few degrees Kelvin. This setup let them recreate what happens when two lonely molecules finally come together in space and get the chance to interact.

The group repeatedly ran the experiment, stopping after different amounts of time to eject the cloud of molecules and check which molecules had been formed. They saw the mixture progress through the expected steps of the recipe. They observed increases of various molecules as they were created and then decreases as they were consumed in the construction of even larger molecules. But as they waited progressively longer and longer, they never caught sight of any benzene rings. The mixture in the chamber eventually just reached a steady amount of C₆H₅⁺, and the final step of the recipe failed to occur.

“Initially we were very confused—and a little irritated—because we could never get the final reaction to happen,” says JILA postdoctoral researcher G. Stephen Kocheril, the lead author of the paper.

After performing several runs of the experiment and analyzing the data, the team concluded that the expected chain of events wasn’t happening and there must be something else occurring to produce all the benzene in space.

“None of the models now actually predict what's out there,” Lewandowski says. “If you look at observations of how many of these molecules we have out there, no model works. So we sort of said, ‘this model isn't it.’ We don't have a new model yet; that's what we're working on now. So it was kind of big for the community because it changed how larger and larger carbon-containing molecules are formed in space.”

Moving beyond the old explanation gives chemists insights into how they should think about the formation of these molecules and provides astronomers with new clues about which molecules they should be keeping an eye out for if they want to understand the chemistry happening out in the interstellar medium.

JILA Fellow and University of Colorado Boulder Physics Professor Heather Lewandowski and members of her lab have shattered a 25-year-old theory about how benzene forms in the interstellar medium, revealing that the long-accepted chemical recipe doesn’t work under space-like conditions. Their groundbreaking laser-cooling experiments open a new chapter in understanding the origins of complex carbon molecules in the cosmos.

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Narrowing In: Cooling Molecules with Light Like Never Before

Steven Burrows — Tue, 23 Dec 2025 18:23:49 +0000

Narrowing In: Cooling Molecules with Light Like Never Before Steven Burrows Tue, 12/23/2025 - 11:23

Kenna Hughes-Castleberry / JILA Science Communicator

Narrowline Laser Cooling and Spectroscopy of Molecules via Stark States. Image credit: Steven Burrows / JILA

Atoms have long been the cornerstone of laser cooling experiments. Their relatively simple structure makes them straightforward to cool with light, allowing scientists to achieve temperatures near absolute zero. Molecules, by contrast, present a much more formidable challenge. With complex rotational, vibrational, and electronic states, they’re significantly harder to tame.

Now, in a study published in Physical Review X Quantum, a team led by JILA and NIST Fellow and University of Colorado Boulder physics professor Jun Ye has demonstrated—for the first time—narrowline laser cooling of a molecule. By utilizing a previously unaddressed transition in the diatomic molecule yttrium monoxide (YO), the researchers have developed a new approach to manipulate internal states and molecular motion with unprecedented precision.

The advance not only redefines the quantum state control available to laser-cooled molecules, but also lays the foundation for future advancements in quantum simulation, precision measurement, and the potential development of a molecular clock.

From Nuisance to Narrowline

This research relies on a unique property of the yttrium monoxide (YO) molecule: the existence of a long-lived excited electronic state. The longer natural lifetime an excited state possesses, the narrower its transition linewidth is. And these extraordinarily narrow features enable unparalleled spectroscopic precision and can be used to cool molecules below currently achievable temperatures.

It is worth noting that although the long-lived excited state in YO offers immense potential, until recently, it had only provided additional challenges. “If anything, I would say this excited state has historically been a nuisance to laser cooling,” says JILA graduate student Kameron Mehling, the paper’s first author. “Its very presence forced us to modify the already complicated photon cycling schemes necessary to cool YO to begin with.”

Nevertheless, the JILA team has finally harnessed the long-lived electronic state in YO, more than a decade after the idea was initially proposed. By precisely addressing the narrow transition with an ultra-stable laser, they were able to slow down the motion of the molecules (cooling them) via the newly addressed excited state.

Molecules can be cooled with laser light by continuously scattering photons — a technique where matter repeatedly absorbs and emits photons over and over, removing energy and entropy in the process. While this technique has become commonplace for atoms, molecules are trickier due to their extra complexity: they rotate, vibrate, and possess close-lying opposite parity states, making it hard to keep the cycle going.

“This excited state has been continuously occupied as a decay pathway within our previously implemented cycling schemes,” Mehling explains. “However, this is the first time that we’re directly exciting it and exploring the resulting physics.”

The team’s results rely on one of the most accurate spectroscopic measurements ever made in a laser-cooled molecule—resolving the narrowline transition frequency to 11 digits of precision. This highlights the potential of narrowline transitions in laser-cooled molecules for future precision experiments and opened the door for laser cooling.

Expanding the Molecular Control Toolbox

To make narrowline laser cooling practical, the team had to address a longstanding challenge: preventing the molecules from leaking out of the cooling cycle. Their solution came from an unexpected but powerful source—an applied electric field.

In YO, certain energy states come in nearly identical pairs of opposite parity—like twins (think Kameron and Kendall Mehling) with mirrored personalities. It might seem subtle, but mixing up the twins opens unwanted photon “communication” channels and jeopardizes the photon cycling scheme. However, by applying a small electric field, the researchers could identify and isolate a single metastable excited state (i.e. twin) which the laser could repeatedly interact with.

“You have to use another tool in the toolbox,” says JILA postdoctoral researcher Simon Scheidegger.

“Usually in atomic experiments, researchers use light and magnetic fields. But for this, we had to bring in electric fields to isolate the states we care about.”

And the amount of electric field needed? Surprisingly small!

“Other molecular experiments might need 10 to 20 kilovolts per centimeter to observe a similar effect” notes Scheidegger. “We apply fields four orders of magnitude smaller, requiring less voltage than what’s in a AA battery.”

Cooling on the Fly

To demonstrate laser cooling, the team prepared a cloud of ultracold YO molecules and let them fall freely under gravity. While the molecules dropped, they were exposed to carefully tuned laser light and their change in temperature was recorded as the laser frequency was varied.

Despite a brief interaction window, the results were clear: the technique cooled the molecules by a small but significant amount. “Currently we’re limited by how many photons we can scatter off the molecules,” says JILA postdoctoral researcher Logan Hillberry. “Nevertheless, at ultralow temperatures, you are fighting for every additional cooling photon.” The fact laser cooling was demonstrated with only a handful of photons per molecule is particularly impressive —a testament to the technique's efficiency!

“This initial laser cooling demonstration proves we can implement a photon cycling scheme on our narrowline transition, however, there is still plenty of work to be done” says Mengjie Chen, another graduate student on the project. “Since our molecular structure is very well understood, we know we could greatly enhance the cooling effect with only a couple more laser tones.” These future upgrades, along with incorporating the narrowline laser cooling scheme while molecules are trapped in an optical potential, would help initialize record phase space densities and reach currently inaccessible temperatures.

How a Narrow Transition Unlocks Broad Applications

These results suggest more than just a technical milestone— it is a “planting the flag” moment, as the team put it. Narrowline transitions have enabled some of our most precise experiments, like atomic clocks and ongoing searches for fundamental physics. Extending that precision to molecules will unlock entirely new physics. Beyond just laser cooling, the team envisions broad applications across quantum simulation and precision measurements —where molecules are suited to outperform laser-cooled atoms due to their strong electric dipoles. “We’ve built the platform. We’ve demonstrated the tools,” says Mehling. “Now the sky’s the limit.”

In a study published in Physical Review X Quantum, a team led by JILA and NIST Fellow and University of Colorado Boulder physics professor Jun Ye has demonstrated—for the first time—narrow-line laser cooling of a molecule. By utilizing a previously unaddressed transition in the diatomic molecule yttrium monoxide (YO), the researchers have developed a new approach to manipulate internal states and molecular motion with unprecedented precision.

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