Jun Ye

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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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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Dr. Kai Li of JILA’s Jun Ye Group Wins 2026 European XFEL Young Scientist Award

Steven Burrows — Tue, 27 Jan 2026 23:07:48 +0000

Dr. Kai Li of JILA’s Jun Ye Group Wins 2026 European XFEL Young Scientist Award Steven Burrows Tue, 01/27/2026 - 16:07

Photo of Kai Li

JILA is proud to announce that Dr. Kai Li, a researcher in the Jun Ye Group, has been named the recipient of the 2026 European XFEL Young Scientist Award. This prestigious honor is awarded annually to an early-career scientist who has made exceptional contributions through experiments conducted at the European X-ray Free-Electron Laser (XFEL), one of the world’s most advanced facilities for probing matter on atomic length and time scales.

The award is particularly significant because it recognizes not only technical excellence but also creativity in exploiting the XFEL’s unique capabilities to push the boundaries of science. The European XFEL produces ultra-intense, ultrafast X-ray pulses that enable researchers to capture real-time snapshots of molecular and atomic processes with atomic-scale resolution—capabilities that are extremely challenging to achieve using conventional techniques. Reflecting on this achievement, Dr. Li remarked, “It is amazing to see that what was first calculated on paper actually works so well in experiment.” Winning this award places Dr. Li among a select group of scientists shaping the future of ultrafast X-ray science.

At JILA, Dr. Li’s research focuses on precision spectroscopy using ultra-stable and coherent extreme-ultraviolet (XUV) light to investigate the low-energy nuclear transition in thorium-229 (²²⁹Th), a leading candidate for a next-generation nuclear clock. Compared with atomic clocks, a nuclear clock is expected to be far more robust against environmental perturbations and capable of operating at much higher particle densities, potentially enabling breakthroughs in precision timekeeping and searches for new physics, including dark matter detection.

Before joining JILA, Dr. Li earned a Ph.D. in physics from the University of Chicago, where he studied X-ray stimulated Raman spectroscopy. He subsequently completed a postdoctoral appointment at Princeton University, investigating ultrafast energy transfer in strongly coupled light–matter (polaritonic) systems. During this work, he recognized the critical role of high-precision measurement techniques, motivating him to join JILA to develop these capabilities further and apply them to advance XFEL-based science.

As part of the award, Dr. Li will receive a €2,000 prize and deliver a plenary lecture at the European XFEL Users’ Meeting in Hamburg, where leading researchers gather to share breakthroughs in free-electron laser science.

Dr. Kai Li, a researcher in the Jun Ye Group, has been named the recipient of the 2026 European XFEL Young Scientist Award. This prestigious honor is awarded annually to an early-career scientist who has made exceptional contributions through experiments conducted at the European X-ray Free-Electron Laser (XFEL).

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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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Physicist Jun Ye named to Quantum 100 list

Steven Burrows — Fri, 12 Dec 2025 18:36:15 +0000

Physicist Jun Ye named to Quantum 100 list Steven Burrows Fri, 12/12/2025 - 11:36

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

Jun Ye

This week, UNESCO named physicist Jun Ye to its Quantum 100 list—a catalogue of some of the top leaders around the world in the rapidly growing field of quantum science.

Ye holds the Monroe Endowed Professorship in Physics at ��Ҵ�ý�ƽ�� and is a fellow at JILA and the National Institute of Standards and Technology (NIST). Among other research goals, Ye has revolutionized how scientists measure time, developing quantum technologies that can track the passage of time with never-before-seen accuracy and precision.

Ye is “recognized for his curiosity and his hands-on approach to experimentation,” according to the Quantum 100 list. “He has built a world-class research program using light, atoms, molecules, and advanced optical tools to explore nature with unprecedented precision.”

The recognition is part of the 2025 International Year of Quantum Science and Technology, which marks the 100th anniversary of what scientists often consider the beginning of quantum mechanics.

“I love this remarkable piece of science, which connects profound secrets of nature to our growing capabilities of revealing them,” Ye said. “The Year of Quantum has further strengthened the ideal that collaboration among scientists will help us to harness quantum science for building better and more meaningful lives for all of us in the world.”

Ye earned his PhD from ��Ҵ�ý�ƽ�� in 1997 where he trained under Jan Hall, who went on to win a Nobel Prize in 2005. Ye returned to JILA in 1999 and has received numerous awards for his research, including the 2022 Breakthrough Prize in Fundamental Physics.

“We are thrilled that Jun Ye has been identified as one of the Quantum 100 as part of the International Year of Quantum Science and Technology,” said Senior Vice Chancellor for Research and Innovation and Dean of the Institutes Massimo Ruzzene. “Jun’s groundbreaking research, visionary leadership, and unwavering commitment to collaboration and mentorship have been instrumental in driving quantum innovation at ��Ҵ�ý�ƽ��, JILA, NIST and across the Front Range, setting a global standard of excellence.”

Ye leads several quantum research initiatives at JILA. They include the CUbit Quantum Initiative and the Quantum Systems through Entangled Science and Engineering (Q-SEnSE) center funded by the U.S. National Science Foundation.

At JILA, Ye pioneered the design of optical atomic clocks, devices that measure time by tapping the behavior of atoms and electrons. His lab’s clocks would neither gain nor lose a second over billions of years.

Ye and his team have also worked to transform insights into the quantum world into technologies that can improve people’s lives. His lab, for example, built laser-based devices that can analyze samples of human breath, screening people for COVID-19 infections and other health conditions.

The Quantum 100 list also includes Chris Monroe who earned his doctorate in physics from ��Ҵ�ý�ƽ�� in 1992 and whose investment established Ye’s endowed professorship.

UNESCO stands for the United Nations Educational, Scientific and Cultural Organization, a specialized agency of the UN focused on fostering peace, security, and human rights through international cooperation in education, science, and culture. It develops educational tools, promotes cultural heritage, works on scientific endeavors like climate change, and designates World Heritage Sites to preserve globally significant places.

UNESCO named physicist Jun Ye to its Quantum 100 list—a catalogue of some of the top leaders around the world in the rapidly growing field of quantum science.

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JILA and NIST Fellow Jun Ye Named Clarivate Highly Cited Researcher for 12th Consecutive Year

Steven Burrows — Thu, 13 Nov 2025 21:13:42 +0000

JILA and NIST Fellow Jun Ye Named Clarivate Highly Cited Researcher for 12th Consecutive Year Steven Burrows Thu, 11/13/2025 - 14:13

Steven Burrows / JILA Science Communications Manager

JILA and NIST Fellow Jun Ye has once again been recognized as one of the world’s most influential scientists. For the 12th year in a row, Ye has earned a place on the Clarivate Highly Cited Researchers list, an honor reserved for researchers whose work ranks among the top 1% of citations globally across their fields.

This distinction highlights Ye’s sustained impact on atomic, molecular, and optical physics, as well as his pioneering contributions to precision measurement and quantum science. His research has transformed technologies such as optical atomic clocks, setting new standards for timekeeping and enabling breakthroughs in navigation, telecommunications, and tests of fundamental physics.

Clarivate’s Highly Cited Researchers program identifies scientists who have demonstrated broad and significant influence, based on rigorous evaluation of citation data and expert analysis. In 2025, only about 1 in 1,000 researchers worldwide achieved this recognition, underscoring the exceptional nature of Ye’s achievement.

Ye’s continued presence on this list reflects not only his scientific excellence but also his leadership in advancing quantum research initiatives, including the CUbit Quantum Initiative and the Q-SEnSE institute, which are shaping the future of quantum technologies.

For more details on the Highly Cited Researchers program and its selection process, visit Clarivate’s official site.

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JILA Joins DOE’s Quantum Systems Accelerator for Next Phase of Quantum Innovation

Steven Burrows — Tue, 04 Nov 2025 19:18:36 +0000

JILA Joins DOE’s Quantum Systems Accelerator for Next Phase of Quantum Innovation Steven Burrows Tue, 11/04/2025 - 12:18

Steven Burrows / JILA Science Communications Manager

A round glass cell (centre, in black frame) is designed to hold a gas of molecules cooled to 50 billionths of a Kelvin. Credit: Ye Group/Steven Burrows/JILA

The U.S. Department of Energy (DOE) has announced a $625 million investment to advance the next phase of the National Quantum Information Science Research Centers, a cornerstone of the National Quantum Initiative. This funding will support five centers dedicated to accelerating quantum technologies that promise transformative impacts on science, industry, and national security.

Among these centers, the Quantum Systems Accelerator (QSA)—led by Lawrence Berkeley National Laboratory—will continue its mission to develop practical quantum systems that can solve real-world problems. QSA brings together leading institutions to tackle challenges in quantum computing, sensing, and networking, aiming to bridge the gap between theoretical advances and deployable technologies.

JILA is proud to remain a key partner in QSA through the Q-SEnSE Institute, which focuses on quantum sensing and precision measurement. These capabilities are essential for applications ranging from navigation and timing to probing fundamental physics. JILA Fellow Jun Ye will lead the JILA effort, supported by senior investigators and JILA Fellows Cindy Regal, Adam Kaufman, Ana Maria Rey, James Thompson, Murray Holland, and Xun Gao—a team internationally recognized for pioneering work in quantum optics, atomic physics, and many-body systems.

“JILA is proud to remain a key partner in QSA. Through our work in both QSA and Q-SEnSE, JILA plays a leading role in advancing quantum innovations at the national and international levels,” remarked Inese Berzina-Pitcher, Executive Director for Q-SEnSE.

The next five years of QSA will focus on building scalable quantum platforms, advancing error correction, and integrating quantum devices into scientific workflows. JILA’s expertise in ultracold atoms, optical lattices, and quantum simulation will play a critical role in these goals.

For more details, read the official announcements:

Energy Department Announces $625 Million to Advance the Next Phase of National Quantum Information Science Research Centers

The Quantum Systems Accelerator Embarks on Next Five Years of Pioneering Quantum Technologies for Science

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Entangled Time: Pushing Atomic Clocks Beyond the Standard Quantum Limit

Steven Burrows — Thu, 23 Oct 2025 16:24:51 +0000

Entangled Time: Pushing Atomic Clocks Beyond the Standard Quantum Limit Steven Burrows Thu, 10/23/2025 - 10:24

Steven Burrows / JILA Science Communications Manager

Artistic representation of an atomic clock breaking the Standard Quantum Limit. Image credit: Steven Burrows / JILA

Imagine you're trying to keep time by listening to a room full of people clapping. If everyone claps randomly, it’s hard to tell the rhythm. But if they clap in sync, the beat becomes clear and steady. Now imagine you could gently guide them to clap more in unison—not perfectly, but just enough to reduce the noise. That’s what JILA researchers have done with atoms in a clock.

Their results, published in Physical Review Letters, show that it’s possible to go beyond what’s known as the Standard Quantum Limit (SQL)—a fundamental barrier in quantum measurements—by using a technique called spin squeezing. This work could help improve everything from GPS systems to tests of gravity and the nature of the universe.

What Limits a Clock’s Precision?

Atomic clocks are among the most precise instruments ever built. They work by measuring the frequency of light that causes atoms to jump between energy levels. These transitions are incredibly stable, making them ideal for keeping time. But there’s a catch. Each atom behaves independently, and their random quantum behavior adds noise to the measurement. This randomness is what defines the Standard Quantum Limit. It’s like trying to hear a single beat in a noisy crowd.

To reduce this noise, scientists often increase the number of atoms. The more atoms you measure, the better your estimate—kind of like averaging more coin flips to get closer to 50/50. But packing too many atoms together causes them to interact in ways that shift the clock frequency, introducing new errors. So instead of adding more atoms, the JILA team tried something different: they made the atoms entangled.

Entanglement is a quantum connection between particles. When atoms are entangled, their random quantum behavior becomes linked—even if they’re not touching. In this experiment, the researchers used entanglement to make the atoms behave more like a team, reducing the noise in their collective signal.

This approach allows the clock to beat the SQL, achieving better precision without needing more atoms. It’s a clever way to get more information out of the same number of particles.

Entanglement through Nondemolition Measurement

To entangle the atoms, researchers Dr. Yang Yang, Maya Miklos, and their lab mates used a method called quantum nondemolition (QND) measurement. This means they could measure the atoms without disturbing them too much, like checking the temperature of soup without taking the lid off.

They trapped about 30,000 strontium atoms in a grid of laser light called a two-dimensional optical lattice. This setup holds the atoms in place and keeps them cold—less than a millionth of a degree above absolute zero. Cold atoms move less, which helps maintain their coherence and reduces unwanted interactions.

The atoms were placed inside an optical cavity, which bounces light back and forth to enhance its interaction with the atoms. By shining a special probe light into the cavity, the researchers could gently measure the atoms’ collective spin—a property related to their energy state—without collapsing their individual quantum states. The team also used a technique called spin echo to cancel out unwanted shifts caused by the probe light. This helped preserve the delicate quantum state of the atoms during the measurement.

This process “squeezes” the uncertainty in one direction, reducing the noise in the measurement. It’s like squeezing a balloon: the uncertainty gets smaller in one direction but bigger in another. For clocks, this trade-off is worth it because it makes the timing signal more precise when one measures along the squeezed direction.

Putting the Squeezed Clock to the Test

To see if their entangled clock really worked better, the researchers compared two groups of atoms in a “synchronous comparison” between two atomic ensembles. By comparing two clocks at the same time, they could cancel out common sources of noise—like fluctuations in the laser used to probe the atoms. This allowed them to isolate the improvement due to spin squeezing: they can compare the case where both samples are regular, unentangled atoms (called a coherent spin state, or CSS), to where each sample is prepared in a spin-squeezed state (SSS) to see the improved stability from spin squeezing.

They studied how precisely the clock comparison signal could be measured over time. The spin-squeezed clock showed a 2.0 decibel improvement beyond the Standard Quantum Limit. That might not sound like much, but in the world of precision measurement, it’s a significant step forward. They found that the spin-squeezed clock not only beat the SQL but also showed a 3.3 dB improvement over the unentangled clock. This confirms that the entanglement was not just a theoretical benefit—it made a real difference in the clock’s performance.

Over a 43-minute test, the clock reached a fractional frequency uncertainty of 1.1 × 10⁻¹⁸. That means it could detect a change in time as small as one second over the age of the universe. This is the most precise entanglement-enhanced clock ever demonstrated, proving that such entanglement could in the future help make the world’s best clocks even more precise.

Why Does This Matter?

This research is part of a broader effort at JILA to explore how quantum physics can improve measurement tools. JILA Fellows Adam Kaufman and James Thompson are also exploring the use of entanglement for better measurement precision. Atomic clocks are already used in GPS satellites, telecommunications, and tests of fundamental physics. Making them even more precise opens new possibilities. A key challenge is to demonstrate genuine quantum advantage where an entangled clock can reach a performance level superior to the best clock today.

For example, ultra-precise clocks can measure tiny differences in gravity across short distances. This could help scientists study how gravity affects quantum systems or even searches for new physics beyond Einstein’s theories.

The techniques developed in this study—like spin squeezing and QND measurements—could also be used in other quantum technologies, such as sensors and quantum computers. These tools rely on the same principles of coherence and entanglement to perform tasks that classical systems can’t.

Looking ahead, the team hopes to improve their system by using three-dimensional optical lattices, which offer even better control over the atoms. They’re also exploring new ways to amplify signals using time-reversal techniques and quantum optimization algorithms.

There is also growing interest in using entangled clocks to probe the interface between quantum mechanics and gravity. Recent studies together with JILA Fellow Ana Maria Rey and external collaborators at University of Innsbruck have explored how mass-energy equivalence and gravitational gradients affect entangled states, raising fundamental questions about the nature of time and space.

A New Chapter in Quantum Timekeeping

By using entanglement to reduce quantum noise, JILA researchers have taken a meaningful step toward the next generation of atomic clocks. Their work shows that it’s possible to go beyond traditional limits by carefully engineering both the quantum states of atoms and the tools used to measure them.

As clocks become more precise, they also become more sensitive to the world around them. This opens the door to new experiments in gravity, quantum mechanics, and the structure of space-time itself.

In the end, this research isn’t just about keeping better time—it’s about using time to explore the microscopic and macroscopic side of the universe in new ways.

This research is supported by the US Department of Energy, Office of Science, National Quantum Information, Science Research Centers, Quantum Systems Accelerator; National Science Foundation; V. Bush Fellowship; JILA Physics Frontier Center; and the National Institute of Standards and Technology.

In a new study, researchers led by JILA and NIST Fellow Jun Ye have shown how to make atomic clocks even more precise by leveraging entanglement. This allows the atoms to “tick” more in sync, reducing the randomness that usually limits how precisely we can measure time.

Their results show that it’s possible to go beyond what’s known as the Standard Quantum Limit (SQL)—a fundamental barrier in quantum measurements—by using a technique called spin squeezing. This work could help improve everything from GPS systems to tests of gravity and the nature of the universe.

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Entangled Time: Pushing Atomic Clocks Beyond the Standard Quantum Limit

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