CTQM

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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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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JILA Collaboration Makes Cavity Quantum Electrodynamics into a Team Sport

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

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

Bailey Bedford / Freelance Science Communicator

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Smoother Ticking Through Topology

Steven Burrows — Wed, 06 Aug 2025 17:06:13 +0000

Smoother Ticking Through Topology Steven Burrows Wed, 08/06/2025 - 11:06

Steven Burrows / JILA Science Communications Manager

Imagine walking a tightrope in a windstorm. Every gust threatens to knock you off balance. Now imagine that the rope itself is designed in such a way that it naturally resists the wind, keeping you steady even when conditions are less than ideal. That’s the kind of protection topological physics offers to quantum systems.

In the world of atomic clocks, the “tightrope” is the delicate quantum state of atoms trapped in a lattice of laser light. These states are exquisitely sensitive to time and frequency, which is what makes optical lattice clocks so precise. But they’re also vulnerable to noise—tiny fluctuations in laser intensity, temperature, or magnetic fields can nudge the atoms off their ideal path, degrading the clock’s performance.

The new study, led by JILA postdoctoral researchers Tianrui Xu and Anjun Chu of Ana Maria Rey’s group, together with postdoc Kyungtae Kim of Jun Ye’s group, and in collaboration with James Thompson and JILA visiting Fellow Tillman Esslinger, proposes a way to stabilize these quantum states using the principles of topological phases of matter, a branch of physics that deals with properties that remain unchanged under continuous deformations. In these systems, the quantum states are 'knotted' in its quasimomentum space. Such 'knotting', quantified by the 'topological invariants' of the wavefunctions, remains constant even when the system is perturbed in ways that it does not change the global symmetry of the system.

Rey explains, “while discovering topological phases has been a big deal in condensed matter and atomic physics, what could be even more exciting is figuring out how these systems can help us build better sensors. For example, the quantum Hall effect, a topological state, has already been super useful—it has helped us measure the Hall resistance with incredible precision, which in turn lets us pin down constants like the fine-structure constant and even the elementary electron charge with great accuracy. Right now, atomic clocks are limited by laser noise. Even when we do clever tricks like comparing two clocks at once, we are still not hitting the theoretical limit of how precise they should be. So, the question is, can we use topology to improve state-of-the art clocks? This was the main question we tried to answer, and we found out that indeed it is possible.”

Artistic rendering of topological protection of an optical lattice clock.

Image Credit: Steven Burrows / JILA.

From Quantum Simulation to Quantum Sensing

Over the past decade, JILA has been at the forefront of both quantum simulation and quantum sensing. In one line of research, scientists use ultracold atoms to simulate exotic phases of matter, such as those found in high-temperature superconductors or topological insulators. In another, they build some of the world’s most accurate clocks and sensors, capable of detecting tiny changes in gravity or time dilation across millimeters.

Until now, these two fields have largely developed in parallel. But the new study brings them together, showing that the same topological phases explored in quantum simulators can also enhance the performance of quantum sensors.

At the heart of the proposal is the Su-Schrieffer-Heeger (SSH) model, a simple yet powerful model that provides the essential intuitions of topological phases and phase transitions. Originally developed to describe electrons in polyacetylene, a type of polymer, the SSH model describes a chain of sites with alternating strong and weak connections, leading to topological edge states and the corresponding topological bulk properties, both protected by symmetry.

JILA researchers propose implementing this model in a one-dimensional optical lattice clock (OLC) tilted by gravity or by an applied force. In this setup, known as Wannier-Stark OLC, atomic tunneling between lattice sites can be controlled by laser drives, as demonstrated by the collaboration of the Rey group and Jun Ye’s lab in recent years. In this study, the Rey group proposes to use two laser tones to create a hybrid synthetic lattice combining atomic internal states and the position of the atoms, leading to a natural realization of the SSH model.

One of the key innovations in the study is a new spectroscopic protocol that leverages the topological properties of the SSH model. In conventional Rabi spectroscopy, atoms are driven between two states using a single laser tone, and the resulting oscillations are used to measure the transition frequency between the two states. However, this method is sensitive to noise in the laser amplitude, which can distort the signal.

In the SSH-based protocol, the resulting dynamics of the atomic wavefunctions under two laser tones depends on the 1D topological invariant of the SSH model known as the winding number—a quantity that is robust against many types of noise.

JILA researchers have shown that the winding number can be measured by tracking the displacement of the atomic wavefunction over time. This protocol can thus in-turn be used as a spectroscopic probe for atomic transition frequencies. Numerical simulations show that this “SSH spectroscopy” is less sensitive to both global and local amplitude noise than the traditional Rabi spectroscopy. In particular, the statistical noise scales more favorably with the number of atoms, suggesting that the protocol could be especially useful in future clocks that interrogate millions of atoms simultaneously.

Measuring Gravity with Quantum Pumps

The study also explores how topological physics can enhance matter-wave interferometry, a technique used to measure forces like gravity by splitting and recombining atomic wave packets. In a typical matter-wave interferometer, atoms are pushed apart using a sequence of laser pulses, allowed to evolve in different gravitational potentials, and then brought back together to measure the accumulated phase difference.

However, imperfections in the laser pulses can introduce errors, limiting the sensitivity of the device. To address this, the Rey group proposes using a technique known as Thouless pumping—an adiabatic process in which particles are transported across a lattice by slowly varying the system’s parameters.

In their proposed “topological pumping protocol,” atoms are adiabatically moved apart and then recombined using a sequence of laser-driven transitions that trace out a topologically-nontrivial path in parameter space. Here, a topological non-trivial path means a trajectory that is robust to changes in system parameters. This method is inherently robust to many types of experimentally-relevant noise and can achieve larger separations with lower uncertainty than conventional pulse sequences.

Simulations show that the topological protocol outperforms traditional methods in terms of both signal strength and noise resilience, especially when the number of atoms is large. This could pave the way for new types of interferometers capable of measuring gravitational gradients or testing fundamental physics with reduced sensitivity to experimental noise.

Topologically Enhanced Clocks

The proposed protocols are designed to be compatible with existing optical lattice clock platforms, such as those developed in Jun Ye’s lab at JILA. These clocks already operate with extraordinary precision—recent experiments have achieved fractional uncertainties below 10⁻¹⁸—but further improvements are needed to reach the standard quantum limit (SQL), the ultimate sensitivity allowed by quantum mechanics for uncorrelated atoms.

By reducing classical noise, the topological approach offers a practical path toward SQL-limited performance. It also opens the door to new applications, such as measuring gravitational redshifts over even shorter distances or detecting tiny variations in fundamental constants.

Moreover, the study suggests that the same principles could be extended to more complex systems, including higher-dimensional lattices or atoms with multiple internal states. This could enable the exploration of richer topological phases and their potential benefits for quantum sensing and metrology.

In the quantum world, precision often comes at the cost of fragility. But topology offers a way to have both precision and protection. By embedding topological structures into the architecture of optical lattice clocks, the Rey group has outlined a strategy for making these devices more resilient to noise, more sensitive to signals, and more versatile in their applications.

As JILA researchers continue to refine these protocols and bring them into the lab, we may soon see a new generation of quantum sensors that are not only more accurate, but also more robust, thanks to the hidden geometry of quantum states.

This research is supported by the U.S. Air Force Office of Scientific Research, the U.S. Department of Energy Office of Science, National Quantum Information Science Research Centers, Quantum Systems Accelerator, NIST, NSF, Swiss National Science Foundation, Heising-Simons Foundation, Simons Foundation, and Sloan Foundation.

In a new theoretical study, physicists at JILA and the University of Colorado Boulder have proposed a way to make the most precise clocks in the world even more robust—by weaving in the strange, protective properties of topological physics. Their work, published in PRX Quantum, explores how a class of quantum states known as symmetry-protected topological (SPT) phases could be used to improve the performance of optical lattice clocks, a cornerstone of modern precision measurement.

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New quantum navigation device uses atoms to measure acceleration in 3D

Steven Burrows — Wed, 11 Jun 2025 17:15:39 +0000

New quantum navigation device uses atoms to measure acceleration in 3D Steven Burrows Wed, 06/11/2025 - 11:15

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

In a new study, physicists at JILA and the University of Colorado Boulder have used a cloud of atoms chilled down to incredibly cold temperatures to simultaneously measure acceleration in three dimensions—a feat that many scientists didn’t think was possible.

The device, a new type of atom “interferometer,” could one day help people navigate submarines, spacecraft, cars and other vehicles more precisely.

“Traditional atom interferometers can only measure acceleration in a single dimension, but we live within a three-dimensional world,” said Kendall Mehling, a co-author of the new study and a graduate student in the Department of Physics at ��Ҵ�ý�ƽ��. “To know where I'm going, and to know where I’ve been, I need to track my acceleration in all three dimensions.”

The researchers published their paper, titled “Vector atom accelerometry in an optical lattice,” this month in the journal Science Advances. The team included Mehling; Catie LeDesma, a postdoctoral researcher in physics; and Murray Holland, professor of physics and fellow of JILA, a joint research institute between ��Ҵ�ý�ƽ�� and the National Institute of Standards and Technology (NIST).

In 2023, NASA awarded the ��Ҵ�ý�ƽ�� researchers a $5.5 million grant through the agency’s Quantum Pathways Institute to continue developing the sensor technology.

The new device is a marvel of engineering: Holland and his colleagues employ six lasers as thin as a human hair to pin a cloud of tens of thousands of rubidium atoms in place. Then, with help from artificial intelligence, they manipulate those lasers in complex patterns—allowing the team to measure the behavior of the atoms as they react to small accelerations, like pressing the gas pedal down in your car.

Today, most vehicles track acceleration using GPS and traditional, or “classical,” electronic devices known as accelerometers. The team’s quantum device has a long way to go before it can compete with these tools. But the researchers see a lot of promise for navigation technology based on atoms.

“If you leave a classical sensor out in different environments for years, it will age and decay,” Mehling said. “The springs in your clock will change and warp. Atoms don’t age.”

Fingerprints of motion

Interferometers, in some form or another, have been around for centuries—and they’ve been used to do everything from transporting information over optical fibers to searching for gravitational waves, or ripples in the fabric of the universe.

From left to right, Kendall Mehling, Murray Holland and Catie LeDesma in their lab at ��Ҵ�ý�ƽ��. Image credit: Glenn Asakawa / ��Ҵ�ý�ƽ��

The general idea involves splitting things apart and bringing them back together, not unlike unzipping, then zipping back up a jacket.

In laser interferometry, for example, scientists first shine a laser light, then split it into two, identical beams that travel over two separate paths. Eventually, they bring the beams back together. If the lasers have experienced diverging effects along their journeys, such as gravity acting in different ways, they may not mesh perfectly when they recombine. Put differently, the zipper might get stuck. Researchers can make measurements based on how the two beams, once identical, now interfere with each other—hence the name.

In the current study, the team achieved the same feat, but with atoms instead of light.

Here’s how it works: The device currently fits on a bench about the size of an air hockey table. First, the researchers cool a collection of rubidium atoms down to temperatures just a few billionths of a degree above absolute zero.

In that frigid realm, the atoms form a mysterious quantum state of matter known as a Bose-Einstein Condensate (BEC). Carl Wieman, then a physicist at ��Ҵ�ý�ƽ��, and Eric Cornell of JILA won a Nobel Prize in 2001 for creating the first BEC.

Next, the team uses laser light to jiggle the atoms, splitting them apart. In this case, that doesn’t mean that groups of atoms are separating. Instead, each individual atom exists in a ghostly quantum state called a superposition, in which it can be simultaneously in two places at the same time.

When the atoms split and separate, those ghosts travel away from each other following two different paths. (In the current experiment, the researchers didn’t actually move the device itself but used lasers to push on the atoms, causing acceleration).

“Our Bose-Einstein Condensate is a matter-wave pond made of atoms, and we throw stones made of little packets of light into the pond, sending ripples both left and right,” Holland said. “Once the ripples have spread out, we reflect them and bring them back together where they interfere.”

When the atoms snap back together, they form a unique pattern, just like the two beams of laser light zipping together but more complex. The result resembles a thumb print on a glass.

“We can decode that fingerprint and extract the acceleration that the atoms experienced,” Holland said.

Planning with computers

The group spent almost three years building the device to achieve this feat.

“For what it is, the current experimental device is incredibly compact. Even though we have 18 laser beams passing through the vacuum system that contains our atom cloud, the entire experiment is small enough that we could deploy in the field one day,” LeDesma said.

One of the secrets to that success comes down to an artificial intelligence technique called machine learning. Holland explained that splitting and recombining the rubidium atoms requires adjusting the lasers through a complex, multi-step process. To streamline the process, the group trained a computer program that can plan out those moves in advance.

So far, the device can only measure accelerations several thousand times smaller than the force of Earth’s gravity. Currently available technologies can do a lot better.

But the group is continuing to improve its engineering and hopes to increase the performance of its quantum device many times over in the coming years. Still, the technology is a testament to just how useful atoms can be.

“We’re not exactly sure of all the possible ramifications of this research, because it opens up a door,” Holland said.

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Where Motion Meets Spin: A Quantum Leap in Simulating Magnetism

Steven Burrows — Thu, 24 Apr 2025 18:11:43 +0000

Where Motion Meets Spin: A Quantum Leap in Simulating Magnetism Steven Burrows Thu, 04/24/2025 - 12:11

Kenna Hughes-Castleberry / JILA Science Communicator

The strange behaviors of high-temperature superconductors—materials that conduct electricity without resistance above the boiling point of liquid nitrogen—and other systems with unusual magnetic properties have fascinated scientists for decades. While researchers have developed mathematical models for these systems, much of the underlying quantum dynamics and phases remain a mystery because of the immense computational difficulty of solving these models.

In a new study published in Science, researchers from JILA, led by JILA and NIST Fellows and University of Colorado Boulder physics professors Jun Ye and Ana Maria Rey and JILA and ��Ҵ�ý�ƽ�� physics professor John Bohn, used ultracold molecules to realize these models with an unprecedented level of control. Their work bridges the fields of atomic, molecular, and optical (AMO) physics with condensed matter physics, opening new doors for quantum simulations and advances in quantum technologies.

“It is very exciting that experiments with polar molecules are now reaching the point where these models can be implemented in the lab,” Rey says. “While currently, we are exploring dynamics at low filling fractions where theory effort can still have some predicting capabilities, very soon experiments will reach dense regimes intractable by theory, fulfilling the dream of quantum simulation.”

A Decade in the Making

JILA has long been celebrated as a hub where experimentalists and theorists collaborate to tackle some of the most challenging questions in physics. Indeed, over two decades of collaboration among JILA researchers, first with the experimentalists Ye and the late JILA Fellow Deborah Jin, later joined by theory colleagues Rey and Bohn, pioneered ultracold molecule research and laid the foundation for this work.

In this study, the researchers from Ye’s experimental group collaborated with theorists in Rey’s and Bohn’s groups to understand the data from several new experiments exploring different regimes of molecular motion and dipolar interactions.

“We wanted to understand how motion and magnetism are coupled in quantum systems,” says Annette Carroll, a JILA graduate student in the Ye laboratory and the paper’s first author. “The molecules offer a unique platform to study this interplay, thanks to their long-range dipolar interactions.”

Molecules sparsely occupy a deep 3D optical lattice. Molecules interact with induced dipole moments and transition dipole moments represented by squiggly lines between lattice sites. Lowering the lattice depth in the horizontal direction allows tunneling between sites within layers. Image Credit: Steven Burrows / JILA

These dipolar interactions were key to the experiment’s success. While neutral atoms have been widely used in quantum studies due to their ease of cooling and control, their typical short-range interactions often limit their ability to simulate magnetism. Ultracold molecules, with their natural long-range dipolar interactions, offer a richer platform for exploring exotic quantum phases but are more complicated to control.

Focusing on Framework

In the experiment, an array of ultracold potassium-rubidium molecules were used to emulate the behavior of electrons in a solid state crystal. Electrons tunnel between nearby ion cores in a crystal at a rate “t”.

To imitate the fact that electrons are like tiny magnets, which can point in two directions, spin up or spin down, molecules were prepared in two accessible internal (rotational) states. Electrons are charged particles and see each other at a distance, but due to the ion cores and other electrons in the system, they strongly screen each other, and effectively, one electron only sees another electron when they are at the same lattice site. In this setup, two nearby molecules (simulating electrons), one with spin up and one with spin down, can flip their spins but to do that, for example, the spin up electron needs to hop into the site where the down electron is, interact just for a glimpse to reduce the large energy cost to be at the same site, and then hop back to its original site now as a spin down.

This process is called superexchange and happens at a rate “J.” The behavior of electrons hopping and exchanging their spins is called “t-J” model and it is believed to have all the necessary ingredients to explain the emergence of high temperature superconductivity. But, this is not yet well understood.

“Polar molecules have the advantage that they carry a dipole moment, and this means that two molecules can exchange the spins far from the distance without needing to move where the other is. This has great consequences,” elaborates Rey. “It allows us to simulate the ‘t-J’ model in a broader parameter regime since the exchange rate J can be controlled in the lab. It opens exciting opportunities for the exploration of magnetism and superconductivity in new regimes.”

“The t-J model captures the interplay between motion and spin interactions,” adds Sean Muleady, a former JILA graduate student in Rey’s theory group now at the Joint Center for Quantum Information and Computer Science (QuICS) and the Joint Quantum Institute (JQI), who was also involved in this study. “These dynamics are critical to understanding phenomena like magnetism in strongly-correlated systems and, in certain regimes, even superconductivity. But studying these effects in real materials is notoriously difficult.”

To overcome these challenges, Rey, Muleady, and postdoctoral researcher David Wellnitz worked with Bohn and his graduate student Reuben Wang to develop mathematical tools to simulate the spin dynamics of moving dipolar particles within different lattice arrangements set up by the researchers within Ye’s experimental group.

“Using dipolar interactions adds an entirely new dimension,” says Bohn. “This is a more generalized version of the t-J model, incorporating features that condensed matter physicists could only theorize about.”

Combining Theory and Experiment

For the researchers in Ye’s laboratory, the team focused on ultracold potassium-rubidium molecules trapped in an optical lattice—a grid of laser light designed to confine the molecules to specific locations. This lattice structure served as a simulated crystal, mimicking the confinement of electrons in real materials. By applying electric fields, the researchers precisely controlled the strength and nature of the molecules’ dipolar interactions and, by tuning the strength of the optical lattice, tuned their ability to move within the lattice.

The experimentalists studied the dynamics between two distinct motional extremes: one where the molecules were “frozen” in place and another where they could move freely within two-dimensional planes without any transverse lattice confinement. By tuning the transverse lattice depth between these two extremes, the researchers explored a large range of behaviors governed by the t-J model, from interactions between frozen spins to dynamic coupling between spin and motion. In all setups, the researchers prepared the molecules in a superposition of rotational states, simulating magnetic spins all pointing in the same direction, and measured how quickly the spins lost their initial magnetization because of their interactions.

Interpreting these behaviors, however, required an equally flexible theoretical approach. Two theoretical groups, led by JILA Fellows Ana Maria Rey and John Bohn, collaborated to combine their unique expertise. Rey’s group specialized in lattice-based models, while Bohn’s group brought insights into molecular collisions and scattering processes.

“These were two very different schools of thought,” says Muleady. “Bringing them together was critical because the experiment operates in a middle ground that neither approach alone could fully describe.”

The collaboration resulted in novel theoretical frameworks that bridged the gap between frozen and dynamic motional regimes, enabling a comprehensive interpretation of the experimental data.

Connecting Magnetism and Motion

Through their collaboration, the team made several significant discoveries, including that the spins stayed aligned much longer at a particular electric field when the interaction between the spins is independent of their orientation. Observing coherence in this context is crucial because the spins maintain their alignment over time, which is rare. Long coherence times are important for preserving quantum entanglement, a behavior where particles’ quantum states are interdependent.

“At this special point, the spins of the molecules align perfectly, leading to slower decay of quantum coherence than at any other point,” explains Cal Miller, a JILA graduate student in the Ye group. “This is something that had been theorized but never observed in an experiment until now.”

This finding confirmed theoretical predictions about the behavior of spin systems and demonstrated the precise tunability of interactions between molecules.

However, the experimentalists observed other dynamics that required new theoretical modeling. The researchers systematically explored how the coherence between the spins depends on molecular motion, developing for the first time a model of how collisions between molecules allowed to move freely within 2D layers lead to the decoherence of the spins.

“At first, we couldn’t explain why the decoherence behaved this way,” explains Junyu Lin, a postdoctoral researcher in Ye’s group. “It took many discussions. Finally, when we saw the model from Reuben and John, and it matched our data, we thought: ‘Oh, that’s the mechanism.”

Moreover, when the molecules were allowed to move freely, the researchers observed a striking new phenomenon in the spin alignment.

“We saw a fascinating ‘stretched exponential’ behavior in the decay of spin alignment,” says Wang. “It’s a result of the molecules’ motion and their spin alignment—a combination that’s difficult to describe using traditional methods.”

The key understanding from the work is how motion, which can be regulated by optical lattices, affects the magnetization dynamics of strongly interacting dipoles. The researchers observed more complex spin orientation dynamics by allowing the molecules to move. The coupling between spin and motion modifies the rate at which interacting spins evolve.

Pushing New Frontiers in Experiment and Theory

Understanding these experimental discoveries would not have been possible without the team's new advances in theoretical modeling.

“This project pushed our tools to the limit,” explains Wellnitz. “We had to develop new methods to bridge the gap between systems where molecules are frozen and those where they’re moving freely.”

The collaboration also highlighted the challenges and rewards of interdisciplinary research within theoretical physics.

“One of the most exciting parts of this work was finding a shared language between the different theoretical approaches,” says Muleady. “Each group brought something unique to the table, and the experiment provided a real-world test for our models.”

For the experimentalists, these results may bring new interest to the t-J model from multiple different subfields of physics.

“While the condensed matter community is already interested in this model, I think the AMO community will also be more interested in our work because we’re approaching things differently,” adds Lin.

While the results of this study have uncovered vital information about the rich dynamics of long-range interacting spin systems, the researchers are already looking toward the project’s next steps.

For the experimentalists, future work will focus on achieving even colder temperatures and higher densities of molecules.

“We’re working toward regimes where the molecules’ interactions are strong enough to create new quantum phases,” says Carroll. “These are the conditions where we might observe rich phenomena like superfluidity.”

For others, the results of this project suggest major implications for the future development of quantum devices.

“By advancing our understanding of spin-motion coupling, this work could inform the design of new quantum technologies,” notes Wellnitz. “It’s an exciting time to be in this field.”

This research is supported by the National Science Foundation, the US Department of Energy's Office of Science, National Quantum Information Science Research Centers, the Quantum Systems Accelerator, the Air Force Office and Office of Science and Research, and the JILA Physics Frontier Center.

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Combining Machine Learning with Quantum Metrology: Making a Universal Quantum Sensor

Steven Burrows — Mon, 14 Apr 2025 18:18:47 +0000

Combining Machine Learning with Quantum Metrology: Making a Universal Quantum Sensor Steven Burrows Mon, 04/14/2025 - 12:18

Kenna Hughes-Castleberry / JILA Science Communicator

Simulation using the gradiometer protocol. Image credit: Steven Burrows / JILA

Atom interferometry, a technique that leverages the wavelike nature of atoms, has been pivotal in precision measurements, including satellite navigation and measuring the Earth's roundness. Traditional atom interferometry setups, however, often lack flexibility, requiring hardware modifications for performing different measurement tasks.

Addressing this limitation, JILA Fellow and University of Colorado Boulder physics professor Murray Holland and his team, along with ��Ҵ�ý�ƽ�� Engineering Professor Marco Nicotra, developed a platform that combines machine learning with atom interferometry. Recently published in Physical Review Research, their work establishes a programmable framework for quantum sensing, where, using universal programmable atom-optic “gates,” a single device can be reconfigured via software to perform a wide range of precision measurements—such as acceleration, rotation, and gravity gradients—without hardware changes.

This innovation not only advances the flexibility and efficiency of quantum sensors but also lays the groundwork for a new wave of quantum engineering in which future quantum technologies integrate AI-driven control to provide extra precision and functionality.

“Understanding the superposition and interference of particles has been at the heart of quantum for more than a century, but just now we are just beginning to develop the experimental tools to really exploit the ideas and build new future technologies,” Holland says.

Following JILA’s Legacy of Laser Stability

JILA has long been recognized as a global leader in precision measurement, particularly in laser stability and atomic control. Much of this legacy stems from the groundbreaking work of JILA and NIST Fellow Jun Ye, whose pioneering research has redefined the frontiers of ultra-stable lasers and optical atomic clocks.

Building on this tradition, Holland, along with JILA postdoctoral researcher Catie LeDesma and graduate student Kendall Mehling, used ultra-stable lasers as the foundation for their system. These lasers create the optical lattice that traps and manipulates a Bose-Einstein condensate—an ultracold cloud of atoms behaving as a single quantum wave.

To bring the system to life, the team collaborated closely with JILA electronics shop member Terry Brown, who played a critical role in designing and fine-tuning the custom circuitry required to control the lattice’s motion precisely.

“Terry Brown has been a pivotal contributor to our experiment, helping us to understand and build the ultra-low-noise radio-frequency electronics that are core components of our experimental design,” Mehling notes.

Each gate operation—such as splitting, reflecting, or stopping the atom wave-packets—was executed through carefully choreographed shifts in the lattice position. These gates acted like programmable “tiles” that could be arranged sequentially, like LEGO bricks, to build complex atom interferometer circuits. By snapping these elements together in different combinations, the team could effectively program the quantum sensor to perform various measurement tasks—all within the same physical setup.

Adding Machine Learning

What sets this project apart is how the team used machine learning to design the gates or “tiles” in their system. Instead of relying on manually tuned parameters or hard-to-find solutions of mathematical equations, the researchers turned to artificial intelligence to solve the complex problem of finding the precise lattice modulations needed to implement each gate. They used optimization algorithms to train a computer to discover how to dynamically position the optical lattice in just the right way to achieve high-fidelity quantum state transformations. This approach not only streamlined the design process but also uncovered solutions that might be non-intuitive to human inventors.

“Artificial intelligence is a trending theme in the science of today, and our experiment is no exception, where the computers find solutions to our design tasks that would be impossible to envisage without their help,” says LeDesma.

Validating Their Setup

To prove their system worked, the team ran a series of experiments with a Bose-Einstein condensate (BEC) of rubidium atoms trapped in the optical lattice. Using precision imaging, they captured the motion of the atoms in real time as each gate was applied, watching as the atom cloud split, reflected, or froze in place according to the programmed instructions. These visual results were then matched with time-of-flight measurements, where the atoms are released and their wavefunctions allowed to expand, revealing their momentum distribution—an essential tool for verifying the implementation of the state transformations.

The comparison between experimental data and the machine learning simulations showed remarkable agreement. Gates designed purely through computational optimization were realized in the lab with high fidelity, often exceeding 90% accuracy. This confirmed that the AI-designed protocols were viable and could be executed with precision in a real-world quantum system—a significant achievement in quantum control engineering.

Creating Versatile Quantum Sensors

By creating a universal gate platform for atom interferometry, Holland’s team has laid the groundwork for software-defined quantum sensors—devices that can switch functions with a new program rather than a new piece of hardware. What’s more, the fusion of AI and quantum hardware offers a pathway to optimizing these sensors for changing environments. In principle, a future sensor could learn in real time, adjusting its gate sequences on the fly to compensate for noise or to prioritize different measurement axes—opening the door to adaptive, intelligent quantum metrology.

This work is also part of NASA’s Quantum Pathways Institute (QPI), a multi-institutional effort to develop deployable quantum technologies. NASA’s vision includes mobilizing quantum sensors for use in space, where traditional systems may be too rigid or sensitive to operate effectively. The universal gate framework aligns perfectly with this goal—enabling sensors that can be reprogrammed mid-mission to adapt to new objectives or conditions in orbit, on planetary surfaces, or even deep-space missions.

“We think this technology solution that bridges quantum physics and AI will allow us to build new kinds of applications that will bring the fuzzy quantum world out of the lab and into everyday life,” Holland says.

This research was supported by NASA and the National Science Foundation.

Researchers at JILA and the University of Colorado Boulder have developed an innovative platform that combines machine learning with atom interferometry to create a universal quantum sensor. This system uses programmable atom-optic "gates" to reconfigure a single device via software for various precision measurements, such as acceleration, rotation, and gravity gradients, without the need for hardware changes.

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Quantum Teleportation Gets an Ionic 2D Upgrade

Steven Burrows — Fri, 11 Apr 2025 18:21:54 +0000

Quantum Teleportation Gets an Ionic 2D Upgrade Steven Burrows Fri, 04/11/2025 - 12:21

Kenna Hughes-Castleberry / JILA Science Communicator

Teleporting quantum information stored in collective spin states of ions within a two-dimensional crystal. Image credit: Steven Burrows / JILA

Quantum entanglement is one of the most well-studied phenomena in quantum physics. Einstein called it “spooky action at a distance,” as it enables particles to be deeply connected—such that measuring one instantly reveals information about the other, regardless of the distance between them. For decades, quantum entanglement has been used to design protocols for studying other physical processes, including quantum teleportation, which allows the transfer of quantum states without physically moving particles.

While quantum teleportation has been experimentally demonstrated in various settings, including individual photons and ions, extending this protocol to many-body systems—composed of many interacting particles—has remained a significant theoretical challenge. In contrast to isolated particles, many-body systems feature complex interdependencies where quantum information is shared across the entire ensemble. These collective behaviors give rise to rich dynamics and entanglement structures that are essential for quantum technologies but also introduce a level of complexity that makes teleportation more difficult to design and implement.

Now, in a recent study published in Physical Review Research, researchers at JILA—led by JILA and NIST Fellow and University of Colorado Boulder physics professor Ana Maria Rey and her team, along with Klaus Molmer from the Neils Bohr Institute and John Bollinger from NIST—have developed a new protocol for teleporting quantum information stored in collective spin states of ions within a two-dimensional crystal. This approach bridges concepts from atomic physics, quantum optics, and quantum information science, opening new avenues for building modular, scalable systems for quantum information processing.

“Fundamentally, we generate Einstein-Podolsky-Rosen correlations—entanglement—between collective spin systems, using tools experimentally accessible in trapped ions,” explains theorist Muhammad Miskeen Khan, who recently completed his postdoc from JILA and is now a postdoctoral researcher at Saint Louis University. “Then came up with a protocol that used that entanglement as a resource to teleport many-body collective spin states between energetically distinct ensembles.”

“Our proposed teleportation protocol leverages both phonon-mediated collective spin-spin interactions among three energetically separated spin-ensembles in a two-dimensional trapped ions crystal together with measurements and local operations on these ensembles,” Rey says. “We have taken advantage of different nuclear spin levels accessible in the system. Although in the current proposal the suggested protocol depends on spin ensembles that are energetically separated but spatially overlapping, future advancements could be gained from implementing our proposed protocols in spatially separated ensembles, for example, using 3D ion crystals.”

From Individual Ions to Collective Spin Ensembles

In quantum experiments, spin refers to the internal angular momentum of particles such as electrons or atomic nuclei. Like each goose in a flock facing one direction so that the whole flock is facing the same direction, in a system of many atoms, their spins can be treated as a collective spin—a combined property that captures the net behavior of the ensemble. Such collective spin states are helpful in precision measurements and quantum computing, especially when they exhibit quantum correlations such as squeezing or entanglement.

The JILA team designed a teleportation protocol in which these collective states—rather than individual ions—are transferred between ion subgroups within a Penning trap, a system used to trap large systems of ions via a set of electrodes and a strong magnetic field. The system they studied consists of a 2D array of trapped beryllium ions in a crystal, which vibrate coherently through shared vibrations, or phonon modes, which can be used to individually manipulate nuclear and electronic spin states of these ions by driving them with lasers and microwave fields. Instead of spatially separated ion ensembles, the researchers separated the ensembles by using distinct nuclear spin levels (or internal ion levels) within the crystal, which have large energy splittings in the strong magnetic field used in the Penning trap to confine the ions. The investigators used three levels to emulate three independent quantum subsystems: Alice, Bob, and Charlie.

First, Alice and Bob—two ion groups—are linked together through a phonon mode of the entire crystal. This phonon mode acts like a mediator, allowing the spins in Alice and Bob to become entangled and form a correlated quantum state.

Next, the third sub-ensemble or nuclear spin energy level, Charlie, holds a quantum state that the researchers want to teleport. This state is gently combined with Alice’s state to mix their information coherently without measuring it directly—like blending two sound waves before analyzing them.

Finally, both Alice and Charlie quantum states are measured. These measurements don't reveal the full quantum state but provide enough information, which is sent to adjust Bob’s group to end up in the same quantum state that Charlie originally had. The result is that Charlie’s state appears in Bob’s ions, effectively teleporting the quantum information across the system.

The protocol, adapted from continuous-variable teleportation schemes in quantum optics, was successfully numerically simulated in systems containing up to 300 ions per ensemble. The simulation also showed the possibility of achieving a high-fidelity teleportation of classical and non-classical spin states, including spin-coherent, spin-squeezed, and Dicke states, under current experimental conditions. Spin-squeezed and Dicke states are particularly interesting because they exhibit entanglement and are helpful for quantum-enhanced sensing, quantum information processing, and computation.

Demonstrating the teleportation of these states suggests that the protocol could one day serve as a mechanism for distributing entanglement and quantum information processing in quantum networks of ions.

“Typically, teleportation circuits are applied to spin-coherent states, which are relatively easy to prepare and simulate,” Khan notes. “We showed that the same protocol can be extended to non-trivial, entangled states, which had not been clearly demonstrated before in a collective spin setting.”

This theoretical protocol is also experimentally realistic. The proposed platform leverages existing techniques in Penning traps, where ion crystals are cooled, entangled, and interrogated with a high degree of control. The phonon modes in the trap are long-lived, robust to noise, and capable of coupling hundreds of ions simultaneously, making them ideal for entanglement distribution.

Protocols with Many Applications

Teleportation protocols like these could serve as building blocks for special types of quantum devices, where quantum information is moved from one register to another without physical transport. It also lays the groundwork for distributed quantum sensing, where entangled states are shared across separate sensors to improve measurement precision.

Beyond practical applications, this work could be the starting point for implementing schemes relevant to simulating quantum gravity in the lab and quantum information scrambling.

“Currently, we are working on some quantum information protocols implementable in the NIST Penning trap inspired by black hole physics,” JILA graduate student Edwin Chaparro says. “Black holes are believed to be the fastest-scrambling objects in nature. We want to leverage the capability to generate scrambling in ion arrays to perform quantum teleportation and information recovery protocols and quantum metrology applications.”

Looking ahead, the researchers hope to extend the protocol to spatially separated systems, potentially using a new generation of trapped ion crystals that live in three special dimensions instead of two. They also plan to explore how similar schemes could be implemented in other physical platforms, such as neutral atom arrays or polar molecules.

This work was supported by the U.S. Department of Energy’s Office of Science, National Quantum Information Science Research Centers, the Quantum Systems Accelerator, the JILA Physics Frontier Center, and NIST.

Researchers at JILA, led by Ana Maria Rey, developed a new protocol for teleporting quantum information in collective spin states of ions within a two-dimensional crystal. This involves entangling ion groups through phonon modes and using measurements to transfer quantum states. The protocol, successfully simulated with up to 300 ions, shows potential for quantum networks and distributed quantum sensing.

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Making a Leap by Using “Another State to Entangle”

Steven Burrows — Fri, 24 Jan 2025 20:01:43 +0000

Making a Leap by Using “Another State to Entangle” Steven Burrows Fri, 01/24/2025 - 13:01

Kenna Hughes-Castleberry / JILA Science Communicator

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.

Schematic of the multi-level atomic array structure used in this study. Image credit: Steven Burrows / JILA

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.

“We know that including the full multilevel structure of atoms can give us richer physics and new phenomena, which are promising for entangled state generation,” says Agarwal, the paper’s first author. With quantum technologies like computing and secure communications requiring entanglement, understanding how to create stable, interconnected atomic systems has become a priority.

From Two to Four Internal States

For this study, the researchers focused on isolating four energy levels in strontium atoms, arranged in either one-dimensional (1D) or two-dimensional (2D) configurations where the atoms are loaded in a special configuration in which they are closer to each other than the wavelength of the laser light used to excite them.

The study concentrated on a set of internal levels with a much smaller energy separation than typical optical transitions. Instead of using truly ground-state levels, they proposed using metastable levels where atoms can live for a very long time.

This very interesting set of levels has not been explored much before since it requires a special laser with a very long wavelength, but Thompson plans to have this laser in his lab.

“We plan to build the necessary capabilities in our lab to first knock the atom into an excited state that lives for a really long time,” Thompson says. “This will let us use a 2.9-micron wavelength transition between this so-called metastable-state excited-state 3P2 in strontium and another excited-state 3D3 state. This wavelength is about eight times longer than the usual separation between nearby atoms trapped in an optical lattice in our lab. By having a transition wavelength much longer than the trapping light wavelength, we will be able to realize strong and programmable interactions via this photon exchange that happens when the atoms are jammed in close to each other.”

Agarwal adds, “The atoms need to be very close, as interactions weaken with distance, eventually becoming lost due to other sources of decoherence [noise]. Keeping atoms close allows interactions to dominate, preserving the growth of entanglement.”

The team focused on the weak and far-from-resonance regime where atoms are allowed to virtually “trade” photons, i.e., moving them between ground states without permanently occupying an excited state.

“By exchanging photons, atoms are effectively only moving between different configurations in the ground state levels, which simplifies our calculations by reducing the number of states accessible to the system,” Agarwal adds. “It’s easier to eliminate the excited states and focus on the metastable state dynamics, where we observe growing correlations, which furthermore can be preserved when the laser is turned off.

Creating A Spin Model for Entanglement

In the regime where the excited levels are only “virtually” populated, and only atoms can occupy the metastable state levels, the four-level problem can be reduced back to a two-level system at the cost of dealing with much more complex interactions, which involves not only pair-wise interactions but multi-atom interaction.

Rey explains, “We focused in the far from a resonant regime where to leading order, only two atoms interact at a given time. In this case, the Hamiltonian describing the metastable state dynamics maps back to a well-characterized spin model.”

The team used this well-known model to study what are called “spin waves”—coordinated low-energy excitations of atomic spins—across the lattice arrangement. Moreover, by controlling the polarization and propagation direction of the photons of the laser exciting the atoms, the researchers could determine which “spin-wave pattern” became dominantly entangled. The entanglement observed was spin-squeezing, a specific form of entanglement that has increased sensitivity to external noise and thus useful for metrology.

“The spin squeezing in our system can be experimentally measured and serves as a witness of quantum entanglement. Our setup also has possible applications in simulating many-body physics,” Agarwal says.

This finding is especially significant, as it implies that quantum systems could maintain entanglement over long periods, without needing constant intervention to prevent decoherence.

Limitations in Simulations

While the team’s model offered promising insights, it also faced limitations in accurately simulating the system over time. One of the key limitations arose from the dipole-dipole interactions, which, unlike simpler interactions, involve long-range forces that couple atoms both near and far in the lattice. Furthermore, these couplings are anisotropic and depend on the relative orientation of the atomic dipoles, making the system more complex. Each atom interacts differently with its neighbors spaced along different directions in the lattice, leading to varying interaction strengths and signs across the array.

Other popular simulation techniques designed for short-range interactions fail when applied to long-range interactions, as they aren’t equipped to handle the many correlations that develop over time. Although some other methods are more appropriate for long-range atomic interactions, they are constrained to small atom numbers due to their computational complexity, limiting the researchers’ ability to observe the long-time progression of correlations in a large system.

Diving Further into Internal States

The team’s findings could open new avenues in quantum information science and quantum computing, offering a potential path for the development of highly entangled and scalable quantum systems.

“We’re inching closer to systems that could sustain entanglement reliably, which is a crucial step for future quantum applications,” says Agarwal.

Looking forward, the research team plans to explore how more extensive multilevel systems might enhance entanglement potential.

“In atoms like strontium, with as many as 10 ground and excited levels each, the complexity grows significantly, and we want to see how this impacts entanglement,” Agarwal says. “Furthermore, while we have focused here on interactions between atoms in free space, one excited extension is to understand how these interactions can interplay with additional photon-mediated interactions [that are] built when atoms are instead placed inside an optical cavity or in nanophotonic devices,” she adds

“The competition between the infinite range interactions mediated by the cavity photons and the dipole-dipole interactions described here can open fantastic opportunities to harness light-mediated quantum gates, entanglement distribution, and programmable quantum many-body physics,” says Thompson.

This work was supported by the Vannevar Bush Faculty Fellowship (VBFF), the National Science Foundation (NSF), the Joint Institute for Laboratory Astrophysics-Physics Frontier Center (JILA-PFC), the Quantum Systems Accelerator (QSA), and the National Institute of Standards and Technology (NIST)

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.

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No Cavity, No Party: Free-Space Atoms Give Superradiant Transition a Pass

Steven Burrows — Tue, 17 Dec 2024 19:51:10 +0000

No Cavity, No Party: Free-Space Atoms Give Superradiant Transition a Pass Steven Burrows Tue, 12/17/2024 - 12:51

Kenna Hughes-Castleberry / JILA Science Communicator

A pencil-shaped ultracold gas of frozen two-level atoms interacting via photon-mediated interactions, with elastic and inelastic components. A continuous laser drive excites the atoms on-resonance. Atoms also spontaneously emit photons into free-space. Credit: Steven Burrows / JILA

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.

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.

“While our current simulations were able to reproduce the experimental data, and explained why full synchronization cannot take place under current experimental conditions, a remaining open question is whether the phase transition could happen under different conditions, and at higher densities, where our theoretical methods fail and instead a genuine quantum description is required,” explains Rey.

From Experiment to Theory

In physics, solving complex problems often requires the combined efforts of both theorists and experimentalists. Theorists develop mathematical models and simulations to predict how systems should behave. Conversely, experimentalists conduct experiments to test and challenge these predictions. This collaboration helps bridge the gap between abstract ideas and observable phenomena.

“One of the big questions people are trying to answer is if it's possible to create entangled states in different atomic systems,” explains Sanaa Agarwal, a graduate student in Rey’s group and the paper’s first author. “In a cavity system, this is enabled by these collective all-to-all interactions [atoms interacting one-to-one], but in free space, that still needs to be clarified.”

A cavity system can be fine-tuned to drive atoms into specific quantum states. In contrast, free-space systems are less controlled.

“In free space, there are many effects to look at, like interaction-induced frequency,” says Agarwal. “You also have emission into all possible directions, not just predominantly into the cavity system. So, these effects are expected to change the physics in the system, and that's why we started looking into it, and indeed, we found it’s quite different.”

Simulating the Free-Space System

The specific free-space experimental conditions raised the question of whether the observed behaviors were truly superradiant or coincidental.

To answer these questions, the researchers carried out a series of theoretical simulations using a model that accounted for each atom as a dipole, absorbing and emitting photons from the laser and the light emitted by the other atoms.

“This was an interesting challenge, as the number of accessible states increases linearly in the cavity, but in free space, it can increase exponentially with system size,” Rey elaborates. “In many cases, the interactions can be weak enough that simplified treatments are possible, but it was initially not clear if that was going to be the case in this experiment.”

Argawal adds, “We considered a microscopic model, in which every atom acts like a dipole, and used it to study the emergent properties of the entire atomic cloud. The laser beam is a plane wave, imprinting a specific phase pattern on the atoms, which is crucial in determining how the atoms interact.”

The researchers simulated different conditions, including varying laser power and atom density, to see how these factors influenced the system's behavior.

“Our simulations showed that a “mean-field approximation”, which reduces the complexity greatly by treating the atoms as classical magnets, was enough to reproduce the physics,” Rey notes.

This model was validated with more complex approaches to ensure consistent results.

When Theory Agrees with Experiment

“When we were comparing the theory with the data, we were unsure if it would agree,” Agarwal says. “Some of the data was fairly easy to compare because there was less ambiguity in the experimental apparatus. So when our findings agreed with those results, it gave us a vote of confidence that what we're doing makes sense.”

From their simulations, the researchers concluded that while the free-space experiment agreed with the cavity model, within a narrow range of laser intensities and atom densities, the two systems generally behaved very differently. As the laser power increased beyond a certain threshold, the collective effects that gave rise to superradiance in the cavity disappeared into free space, and the atoms acted more like independent emitters rather than a coordinated group.

Further Enhancing Fundamental Physics

These findings open new research avenues in quantum physics and validate the great value of experiment-theory collaborations to gain a better understanding of the underlying physics.

“While our simulations were able to reproduce the experimental observations in the regime where the system is dilute, and the mean-field approximation is valid, it will be very exciting to study new regimes where our current theory models become obsolete and better treatments are required,” Rey adds. “Our group will be looking for ways to improve our calculations and to prepare us for the new exciting measurements coming ahead.”

This work was supported by the JILA Physics Frontier Center (PFC), the U.S. Department of Energy’s Office of Science, the National Quantum Information Science Research Centers’ Quantum Systems Accelerator, and the National Institute of Standards and Technology (NIST).

Written by Kenna Hughes-Castleberry, JILA Science Communicator

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.

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