News & Research Highlights

Dr. Olivia Krohn, a former JILA graduate student and now a postdoctoral researcher at Sandia National Laboratories, has been awarded the prestigious Justin Jankunas dissertation award, given out by the American Physical Society (APS) division of chemical physics at the APS Global Summit conference. This award recognizes exceptional doctoral research that advances the frontiers of physics. Krohn’s award highlights her dissertation research, which bridges the legacy of JILA’s origins in astrophysics with its current role as a global leader in atomic, molecular, and optical (AMO) physics.

For decades, atomic clocks have been the pinnacle of precision timekeeping, enabling GPS navigation, cutting-edge physics research, and tests of fundamental theories. But researchers at JILA, led by JILA and NIST Fellow and University of Colorado Boulder physics professor Jun Ye, in collaboration with the Technical University of Vienna, are pushing beyond atomic transitions to something potentially even more stable: a nuclear clock. This clock could revolutionize timekeeping by using a uniquely low-energy transition within the nucleus of a thorium-229 atom. This transition is less sensitive to environmental disturbances than modern atomic clocks and has been proposed for tests of fundamental physics beyond the Standard Model.

This idea isn’t new in Ye’s laboratory. In fact, work in the lab on nuclear clocks began with a landmark experiment, the results of which were published as the cover article of Nature last year, where the team made the first frequency-based, quantum-state-resolved measurement of the thorium-229 nuclear transition in a thorium-doped host crystal. This achievement confirmed that thorium’s nuclear transition could be measured with enough precision to be used as a timekeeping reference. 

However, to build a precise clock, researchers must fully characterize how the transition responds to external conditions, including temperature. That’s where this new investigation—an “Editor’s Choice” paper published in Physical Review Letters—comes in, as the team studied the energy shifts in the thorium nuclei as the crystal containing the atoms was heated to different temperatures. 

​A team of physicists at the University of Colorado Boulder and the National Institute of Standards and Technology (NIST) has developed a groundbreaking laser-based device capable of analyzing gas samples to identify a vast array of molecules at extremely low concentrations, down to parts per trillion. Their findings were recently published in Nature. 

For over a century, physicists have grappled with one of the most profound questions in science: How do the rules of quantum mechanics, which govern the smallest particles, fit with the laws of general relativity, which describe the universe on the largest scales? 

The optical lattice clock, one of the most precise timekeeping devices, is becoming a powerful tool used to tackle this great challenge. Within an optical lattice clock, atoms are trapped in a “lattice” potential formed by laser beams and are manipulated with precise control of quantum coherence and interactions governed by quantum mechanics. Simultaneously, according to Einstein’s laws of general relativity, time moves slower in stronger gravitational fields. This effect, known as gravitational redshift, leads to a tiny shift of atoms’ internal energy levels depending on their position in gravitational fields, causing their “ticking”—the oscillations that define time in optical lattice clocks—to change. 

By measuring the tiny shifts of oscillation frequency in these ultra precise clocks, researchers are able to explore the influences of Einstein’s theory of relativity on quantum systems. While relativistic effects are well-understood for individual atoms, their role in many-body quantum systems, where atoms can interact and become entangled, remains largely unexplored.

Making a step forward in this direction, researchers led by JILA and NIST Fellows and University of Colorado Boulder physics professors Jun Ye and Ana Maria Rey—in collaboration with scientists at the Leibnitz University in Hanover, the Austrian Academy of Sciences, and the University of Innsbruck—proposed practical protocols to explore the effects of relativity, such as the gravitational redshift, on quantum entanglement and interactions in an optical atomic clock. Their work revealed that the interplay between gravitational effects and quantum interactions can lead to unexpected phenomena, such as atomic synchronization and quantum entanglement among particles. The results of this study were published in Physical Review Letters.

When atoms collide, their exact structure—for example, the number of electrons they have or even the quantum spin of their nuclei—has a lot to say about how they bounce off each other. This is especially true for atoms cooled to near-zero Kelvin, where quantum mechanical effects give rise to unexpected phenomena.  Collisions of these cold atoms can sometimes be caused by incoming laser light, resulting in the colliding atom-pair forming a short-lived molecular state before disassociating and releasing an enormous amount of energy. These so-called light-assisted collisions, which can happen very quickly, impact a broad range of quantum science applications, yet many details of the underlying mechanisms are not well understood. 

In a new study published in Physical Review Letters, JILA Fellow and University of Colorado Boulder physics professor Cindy Regal, along with former JILA Associate Fellow Jose D’Incao (currently an assistant professor of physics at the University of Massachusetts, Boston) and their teams developed new experimental and theoretical techniques for studying the rates at which light-assisted collisions occur in the presence of small atomic energy splittings.  Their results rely upon optical tweezers—focused lasers capable of trapping individual atoms—that the team used to isolate and study the products of individual pairs of atoms.

Researchers at the University of Colorado Boulder have developed a novel method to measure magnetic field orientations using atoms as minuscule compasses. The research, a collaboration between JILA Fellow and CU Boulder physics professor Cindy Regal and Svenja Knappe, a research professor in the Paul M. Rady Department of Mechanical Engineering, was recently published as the cover article in the journal Optica.

Congratulations to JILA graduate students Anya Grafov and Iona Binnie—who conduct their cutting-edge research in the laboratory of JILA Fellows and the University of Colorado Boulder professors Margaret Murnane and Henry Kapteyn—for their outstanding achievements at the MMM Intermag 2025 conference!

Interactions between atoms and light rule the behavior of our physical world, but, at the same time, can be extremely complex. Understanding and harnessing them is one of the major challenges for the development of quantum technologies.

To understand light-mediated interactions between atoms, it is common to isolate only two atomic levels, a ground level and an excited level, and view the atoms as tiny antennas with two poles that talk to each other.  So, when an atom in a crystal lattice array is prepared in the excited state, it relaxes back to the ground state after some time by emitting a photon. The emitted photon does not necessarily escape out of the array, but instead, it can get absorbed by another ground-state atom, which then gets excited. Such an exchange of excitations also referred to as dipole-dipole interaction, is key for making atoms interact, even when they cannot bump into each other. 

“While the underlying idea is very simple, as many photons are exchanged between many atoms, the state of the system can become correlated, or highly entangled, quickly,” explains JILA and NIST Fellow and University of Colorado Boulder physics professor Ana Maria Rey. “I cannot think of a single atom as an independent object. Instead, I need to keep track of how its state depends on the state of many other atoms in the array. This is intractable with current computational methods. In the absence of an external drive, the generated entanglement  typically disappears since all atoms relax to the ground state.” 

Atoms can, however, have more than two atomic levels. Interactions in the system can change drastically if more than two internal levels are allowed to participate in the dynamics.  In a two-level system (weak excitation) with only one photon and, at most, one excited atom in the array, one just needs to track the single excited atom. While this is numerically tractable, it is not so helpful for quantum technologies since the atoms could be thought of more as classical antennas.  

In contrast, by allowing just one additional ground level per atom, even with a single excitation, the number of configurations accessible to the system grows exponentially, drastically increasing the complexity.  Understanding atom-light interaction in multi-level settings is an extremely difficult problem, and up to now it has eluded both theorists and experimentalists.  

Rey explains, “However, it can be extremely useful, not only because it can generate highly entangled states which can be preserved in the absence of a drive since atoms in the ground levels do not decay.’’ 

Now, in a recent study published in Physical Review Letters, Rey and JILA and NIST Fellow James K. Thompson, along with graduate student Sanaa Agarwal and researcher Asier Piñeiro Orioli from the University of Strasbourg, studied atom-light interactions in the case of effective four-level atoms, two ground (or metastable) and two excited levels arranged in specific one-dimensional and two-dimensional crystal lattices. 

JILA Fellow, National Institute of Standards and Technology (NIST) Physicist and University of Colorado Boulder physics professor Dr. Adam Kaufman has been awarded the prestigious Presidential Early Career Award for Scientists and Engineers (PECASE).  President Joe Biden announced that this accolade represents the highest honor conferred by the U.S. government to early-career scientists and engineers who exhibit extraordinary potential and leadership in their respective fields. Kaufman’s groundbreaking contributions to quantum science have cemented his place among nearly 400 recipients recognized for their innovative research and commitment to advancing scientific frontiers.

Shuo Sun, Associate Fellow at JILA and Assistant Professor in the Department of Physics at the University of Colorado Boulder has been awarded a prestigious NSF CAREER Award for his research proposal, “Developing a High-Dimensional Photonic Quantum Register for the Quantum Internet.”

In the quest for ultra-precise timekeeping, scientists have turned to nuclear clocks. Unlike optical atomic clocks—which rely on electronic transitions—nuclear clocks utilize the energy transitions in the atom’s nucleus, which are less affected by outside forces, meaning this type of clock could potentially keep time more accurately than any previously existing technology. 

However, building such a clock has posed major challenges—thorium-229, one of the isotopes used in nuclear clocks, is rare, radioactive, and extremely costly to acquire in the substantial quantities required for this purpose.

Reported recently in a new study published in Nature, a team of researchers, led by JILA and NIST Fellow and University of Colorado Boulder Physics professor Jun Ye, in collaboration with Professor Eric Hudson’s team at UCLA’s Department of Physics and Astronomy, have found a way to make nuclear clocks a thousand times less radioactive and more cost-effective, thanks to a method creating thin films of thorium tetrafluoride (ThF₄). 

Isolated atoms in free space radiate energy at their own individual pace. However, atoms in an optical cavity interact with the photons bouncing back and forth from the cavity mirrors, and by doing so, they coordinate their photon emission and radiate collectively, all in sync. This enhanced light emission before all the atoms reach the ground state is known as superradiance. Interestingly, if an external laser is used to excite the atoms inside the cavity moderately, the absorption of light by the atoms and the collective emission can balance each other, letting the atoms relax to a steady state with finite excitations.

However, above a certain laser energy level, the nature of the steady state drastically changes since atoms inside the cavity cannot collectively emit light fast enough to balance the incoming light. As a result, the atoms keep emitting and absorbing photons without reaching a stable, steady state. While this change in steady-state behaviors was theoretically predicted decades ago, it hasn’t yet been observed experimentally.  

Recent research at the Laboratoire Charles Fabry and the Institut d’Optique in Paris studied a collection of atoms in free space forming an elongated, pencil-shaped cloud and reported the potential observation of this desired phase transition. Yet, the results of this study puzzled other experimentalists since atoms in free space don’t easily synchronize. 

To better understand these findings, JILA and NIST Fellow Ana Maria Rey and her theory team collaborated with an international team of experimentalists. The theorists found that atoms in free space can only partially synchronize their emission, suggesting that the free-space experiment did not observe the superradiant phase transition. These results are published in PRX Quantum. 

Physics lab courses are vital to science education, providing hands-on experience and technical skills that lectures can’t offer. Yet, it’s challenging for those in Physics Education Research (PER) to compare course to course, especially since these courses vary wildly worldwide. 

To better understand these differences, JILA Fellow and University of Colorado Boulder physics professor Heather Lewandowski and a group of international collaborators are working towards creating a global taxonomy, a classification system that could create a more equitable way to compare these courses. Their findings were recently published in Physical Review Physics Education Research.

JILA and NIST Fellow and CU Boulder Physics Professor Jun Ye has been named a 2024 Highly Cited Researcher by Clarivate. This distinction is awarded to scientists whose work ranks in the top 1% of citations globally. Ye, known for his groundbreaking contributions to precision measurement and atomic, molecular, and optical physics, joins an elite list of researchers shaping the forefront of scientific innovation.

Flari Tech Inc., a startup rooted in cutting-edge JILA research, has clinched one of the prestigious 2024 Lab Venture Challenge (LVC) grants from the University of Colorado Boulder, advancing its pioneering work to build a breathalyzer for diagnostics use targeting life-threatening diseases such as lung cancer.  

Developed at JILA by a team led by JILA and NIST Fellow and CU Boulder Physics professor Jun Ye and JILA graduate students Qizhong Liang and Apoorva Bisht, Flari Tech’s innovative diagnostic tool is powered by the Nobel Prize-winning optical frequency comb and aims to bring a novel, non-invasive, faster method for lung cancer detection for clinical use.
 

JILA Fellow and NIST (National Institute of Standards and Technology) Physicist and University of Colorado Boulder Physics professor Adam Kaufman and his team have ventured into the minuscule realms of atoms and electrons. Their research involves creating an advanced optical atomic clock using a lattice of strontium atoms, enhanced by quantum entanglement—a phenomenon that binds the fate of particles together. This ambitious project could revolutionize timekeeping, potentially surpassing the "standard quantum limit" of precision. 

In collaboration with JILA and NIST Fellow Jun Ye, the team highlighted their findings in Nature, demonstrating how their clock, operating under certain conditions, could exceed conventional accuracy benchmarks. Their work advances timekeeping and opens doors to new quantum technologies, such as precise environmental sensors.

In the world of quantum technology, measuring with extreme accuracy is key.  Despite impressive developments, state-of-the-art matter-wave interferometers and clocks still operate with collections of independent atoms, and the fundamental laws of quantum mechanics limit their precision.  

One way to get around this fundamental quantum fuzziness is to entangle the atoms or make them talk so that one cannot independently describe their quantum states. In this case, it is possible to create a situation where the quantum noise of one atom in a sensor can be partially canceled by the quantum noise of another atom such that the total noise is quieter than one would expect for independent atoms. This type of entangled state is called a “squeezed state,” which can be visualized as if one had made a clock hand narrower to tell the time more precisely, a precision that comes at the expense of making the fuzziness along the clock hand worse.  However, preparing spin-squeezed states is no easy feat. 

Up to now, there have been two leading ways to generate squeezed states, using atoms that interact with light. One way, unitary evolution, is by transforming an initially uncorrelated (not entangled) state into a spin-squeezed state via dynamical evolution via a specific type of unitary interaction. One can imagine the initially uncorrelated state as a round piece of dough where your hand slowly squeezes the dough in one direction while making the other direction wider. 

The other way is to perform quantum nondemolition measurements (QND) that allow one to pre-measure the quantum noise and subtract it from the final measurement outcome.  The QND approach has currently realized the largest amounts of observed squeezing between the two methods, but it is not clear which protocol is actually optimal, given fundamental experimental constraints, or even if it would be better to use both protocols at the same time. 

This is why JILA and NIST Fellows and University of Colorado Boulder Physics professors Ana Maria Rey and James K. Thompson and their teams wanted to guide the community on which protocol is best to use under fundamental and realistic experimental conditions. Their results, published in Physical Review Research, revealed that when measurement efficiency is greater than 19%, the QND measurement protocol outperformed unitary dynamical evolution. This finding can have big implications for quantum metrology.

JILA postdoctoral researcher Simon Scheidegger has received the prestigious METAS 2024 Award from the Swiss Physical Society (SPS). Scheidegger, who is part of JILA and NIST Fellow Jun Ye's laboratory group, was awarded for his pioneering research on precise measurements of hydrogen energy levels during his PhD at ETH Zurich. 

The interactions between quantum spins underlie some of the universe’s most interesting phenomena, such as superconductors and magnets. However, physicists have difficulty engineering controllable systems in the lab that replicate these interactions.

Now, in a recently published Nature paper, JILA and NIST Fellow and University of Colorado Boulder Physics Professor Jun Ye and his team, along with collaborators in Mikhail Lukin’s group at Harvard University, used periodic microwave pulses in a process known as Floquet engineering, to tune interactions between ultracold potassium-rubidium molecules in a system appropriate for studying fundamental magnetic systems. Moreover, the researchers observed two-axis twisting dynamics within their system, which can generate entangled states for enhanced quantum sensing in the future. 

An international team of researchers, led by JILA and NIST Fellow and University of Colorado Boulder Physics Professor Jun Ye and his team, has made significant strides in developing a groundbreaking timekeeping device known as a nuclear clock. Their results have been published in the cover article of Nature.