Atomic & Molecular Physics

High-fidelity gates and creation of entangled states in Yb171 nuclear-spin qubits

Steven Burrows — Sun, 22 Mar 2026 18:17:50 +0000

High-fidelity gates and creation of entangled states in Yb171 nuclear-spin qubits Steven Burrows Sun, 03/22/2026 - 12:17

Our paper on preparing entangled states in Yb171 has been accepted in Nature physics! Congratulations to the team! We show high-fidelity gates in the metastable qubit, high-fidelity three-outcome measurements, and coherent mapping of entangled states between the Rydberg, nuclear, and optical qubits. This work suggests several new directions, including in quantum error correction, hybrid digital-analog quantum simulations, and quantum metrology.

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New proposal for using quantum error correction in metrology

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

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

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

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Assembling a superfluid from individual atoms

Steven Burrows — Sun, 22 Mar 2026 18:14:16 +0000

Assembling a superfluid from individual atoms Steven Burrows Sun, 03/22/2026 - 12:14

Since it was first proposed in 2004 by David Weiss and Maxim Olshanii, it has been a goal to see whether atomic rearrangement and high-fidelity ground-state laser cooling could employed to prepare superfluids and low-entropy many-body states of itinerant matter. In this work, we demonstrate such a protocol, opening a new path to assembling ground-state many-body state of bosonic and fermionic quantum systems.

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Micromechanical membranes can be quiet frequency sensors even at high amplitude

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

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

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

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

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

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JILA Fellow Dana Anderson celebrates landmark milestone as Infleqtion goes public on the New York Stock Exchange

Steven Burrows — Mon, 23 Feb 2026 22:43:55 +0000

JILA Fellow Dana Anderson celebrates landmark milestone as Infleqtion goes public on the New York Stock Exchange Steven Burrows Mon, 02/23/2026 - 15:43

Steven Burrows / JILA Science Communications Manager

Dana Anderson, Matt Kinsella, and Infleqtion executives ring the opening bell at the New York Stock Exchange. Image Credit, Infleqtion.

JILA is proud to recognize a major milestone for quantum science and technology as Infleqtion, the quantum technology company founded by JILA Fellow and ��Ҵ�ý�ƽ�� Professor Dana Anderson, has officially gone public on the New York Stock Exchange (NYSE). Infleqtion began trading under the ticker symbol INFQ on February 17, 2026, following completion of its business combination with Churchill Capital Corp X, marking a historic moment for both the company and the broader quantum technology community.

This public debut establishes Infleqtion as the first neutral‑atom quantum technology company to enter public markets — a significant validation of nearly two decades of foundational research that originated at ��Ҵ�ý�ƽ�� and JILA. Founded originally as ColdQuanta and spun out of the University of Colorado Boulder in 2007, Infleqtion has since evolved into a global leader in neutral‑atom quantum computing, precision sensing, and quantum‑enabled technologies.

The company's listing is supported by over $550 million in new capital, drawn from strong shareholder participation and additional PIPE financing. This influx of funding allows Infleqtion to accelerate deployment of practical quantum solutions across aerospace, defense, energy infrastructure, advanced computation, and other mission‑critical sectors.

Infleqtion's expanding technology portfolio includes quantum computers, optical atomic clocks, RF receivers, inertial sensors, and quantum software — systems already in use by NASA, the U.S. Army, the U.S. Department of Energy, and the U.K. government. The company’s collaborations also extend to major industry partners such as NVIDIA, contributing to advancements in logical‑qubit‑based materials science applications. NASA’s contracted Quantum Gravity Sensor Mission, supported by more than $20 million in funding, and the U.S. Army’s $2 million program for resilient navigation and timing exemplify the real-world impact of Infleqtion’s quantum technologies.

This milestone comes during a period of notable recognition for Infleqtion’s founder. Earlier this month, Dana Anderson was elected to the National Academy of Engineering for his pioneering contributions to optical quantum engineering with ultracold atoms — work that helped lay the scientific foundation for Infleqtion’s growth. Anderson’s long-standing vision for neutral‑atom architectures, cultivated through his research at JILA, continues to guide the company’s strategy as it advances quantum solutions for aerospace, national security, energy systems, and scientific computing.

Infleqtion’s public listing also highlights the strength of ��Ҵ�ý�ƽ�� and JILA’s innovation ecosystem. As one of the university’s most successful quantum spinouts, the company contributes to Colorado’s expanding role as a global hub for quantum research and commercialization.

As Infleqtion begins its next chapter as a publicly traded company, JILA celebrates Dana Anderson’s leadership and the transformative scientific achievements that made this moment possible.

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Dana Anderson Elected to the National Academy of Engineering

Steven Burrows — Tue, 10 Feb 2026 20:33:53 +0000

Dana Anderson Elected to the National Academy of Engineering Steven Burrows Tue, 02/10/2026 - 13:33

Steven Burrows / JILA Science Communications Manager

Photo of Dana Anderson

JILA is proud to announce that Professor Dana Z. Anderson, JILA Fellow and Professor of Physics and Electrical, Computer & Energy Engineering at the University of Colorado Boulder, has been elected a Member of the National Academy of Engineering (NAE).

Founded in 1964, the National Academy of Engineering admits new members annually to honor transformative achievements and to advance engineering for the benefit of society. Election to the NAE recognizes individuals who have made outstanding contributions to engineering research, practice, or education, as well as pioneering advances in emerging fields of technology.

As a pioneering figure in optical quantum engineering of ultracold atoms, Anderson has long been at the forefront of translating laboratory science into real-world impact. As Founder and Chief Science Officer of Infleqtion (formerly ColdQuanta), he has helped lead the development of practical quantum systems including clocks, inertial sensors, RF sensors, networks, and quantum computing platforms. His academic research spans quantum optics, atomic physics, atom-chip technologies, and precision measurement, areas in which his group has developed integrated atom interferometers and practical devices based on ultracold atoms.

Reflecting on his election to the NAE, Anderson emphasized the community that helped make it possible: “I owe much to the support that CU Physics, JILA, and Engineering have given me over the years to transition atom-based quantum technology into the ‘real’ world.”

His election highlights the growing influence of quantum engineering as a transformative field and underscores JILA’s leadership at the intersection of fundamental science and technological innovation.

JILA congratulates Professor Anderson on this well-deserved recognition and celebrates his continued contributions to quantum science, engineering, and innovation.

View the official NAE announcement.

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

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

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

Steven Burrows / JILA Science Communications Manager

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

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

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

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

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

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Entangled Time: Pushing Atomic Clocks Beyond the Standard Quantum Limit

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

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

Steven Burrows / JILA Science Communications Manager

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

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

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

What Limits a Clock’s Precision?

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

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

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

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

Entanglement through Nondemolition Measurement

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

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

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

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

Putting the Squeezed Clock to the Test

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

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

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

Why Does This Matter?

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

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

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

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

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

A New Chapter in Quantum Timekeeping

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

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

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

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

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

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

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A Symphony of Light and Atoms: Continuous Lasing and Strong Coupling

Steven Burrows — Mon, 22 Sep 2025 16:41:44 +0000

A Symphony of Light and Atoms: Continuous Lasing and Strong Coupling Steven Burrows Mon, 09/22/2025 - 10:41

Steven Burrows / JILA Science Communications Manager

Experimental setup: continuous lasing of Strontium-88 atoms.

Image credit: Steven Burrows / JILA

Imagine a symphony that never stops. The musicians are atoms, the concert hall that lets their sound build is an optical cavity, and the skilled conductor is a new continuous loading with strong coupling technique—keeping perfect time, seating new players quietly mid-performance, and blending everyone into one steady, pure tone. The 'music' you hear is the single, coherent laser beam emerging from the cavity.

In this experiment, supporting laser beams cool and move the atoms—think of them as the metronome and stage crew, not the performance itself. The performance is the new light the atoms collectively create inside the ring cavity, which then exits as a continuous laser. With this conductor-like control, Professor James K. Thompson, a Fellow of JILA, NIST and the Department of Physics at the University of Colorado, Boulder, and his team, maintain both continuous operation and strong collective coupling between the atoms and the cavity, a key step toward ultra-stable light sources and precision measurement tools.

In a set of papers, published in Nature Physics and Physical Review Letters, the Thompson group demonstrated continuous loading and strong coupling of strontium atoms to a high-finesse optical ring cavity, and continuous recoil-driven lasing with an unexpected pinning of the cavity frequency.

Vera Schäfer, one of the lead researchers, explained, "The original goal of our experiment was to build a continuous superradiant laser, a tool which allows us to make high precision frequency measurements at short timescales. This could help us to explore different regimes to search for dark matter and other new physics."

Zhijing Niu, the graduate student noted, “We managed to realize continuous laser cooling of strontium atoms into an optical ring cavity and to transport them within the cavity. This allowed us to keep a steady stream of extremely cold atoms, which is essential for building a continuous superradiant laser."

Thompson added, "But along the way we found something very curious and unexpected that reflects the fact that nature has a way of self-organizing when you pump energy into a system. We saw laser light coming out of our system when we were just trying to load a very cold gas of atoms between the highly reflective mirrors that form our laser cavity."

Continuous Lasing: Quantum Light Sources

Lasing, or light amplification by stimulated emission of radiation, is a process familiar to many through everyday devices like laser pointers and barcode scanners. Past lasing realized with laser-cooled atoms often involve pulsed operation, where the light source is intermittently active. In contrast, continuous lasing provides a steady stream of coherent light, which is crucial for applications requiring high stability and precision.

The researchers utilized laser-cooled strontium atoms, which were continuously loaded into a high-finesse ring cavity. This setup allowed for the atoms to be trapped and cooled using a series of laser cooling stages, including a three-dimensional red molasses and a vertical slowing beam. The continuous nature of this process ensures that atoms continuously replenished, crucial for sustained lasing.

Niu explained, "We have figured out how to laser cool and load our atoms continuously rather than staggered in time like almost all other experiments in our field do (i.e., cool and load some atoms, briefly do some science, throw them away, repeat).” Thompson added, “However, even before getting a chance to use the very narrow atomic transition, we saw laser light coming out of the cavity, and it would keep going all day long until we went home for the day!"

Recoil-Driven Lasing: The Heartbeat of Quantum Light

To understand recoil-driven lasing, think of a game of pool. When the cue ball strikes another ball, it transfers its momentum, causing the second ball to move. Similarly, in recoil-driven lasing, photons (light particles) transfer their momentum to atoms, causing them to move more quickly. This movement creates a population inversion, a key requirement for lasing.

In traditional lasers, achieving population inversion often involves complex setups and intermittent operation. However, the researchers at JILA have developed a method to maintain this inversion continuously. By using laser-cooled strontium atoms and a high-finesse ring cavity, they have created a system where the atoms are constantly replenished and kept in a low-energy state. This continuous replenishment ensures that the lasing process never stops.

Thompson noted, "We realized that the lasing involved absorbing a photon and then undergoing stimulated emission (the s and e of LASER) to a different momentum state since the atom recoils when it catches a photon of light and then throws it into the cavity.” Niu added, “This appears to be the gain mechanism provided by nature when we put energy into the system via our laser-cooling beams."

The experimental setup: Atoms are cooled and slowed inside a vacuum chamber, until they can be trapped in a lattice inside a cavity (black triangular cavity spacer in the bottom half of the vacuum chamber.) Fluorescence of the atoms can be seen on top in blue from hot atoms interacting with the Zeeman slower laser.

Image credit: Vera Schäfer / JILA

Strong Collective Coupling: Enhancing Atom-Cavity Interactions

In addition to continuous lasing, the study also achieved strong collective coupling of strontium atoms to the optical cavity. This phenomenon occurs when the collective interaction between the atoms and the cavity field is strong enough to significantly alter the properties of the system. The researchers demonstrated this by observing continuous atom-cavity vacuum Rabi splitting, a clear indication of strong coupling. This effect is akin to a dance where the atoms and the cavity photons are in perfect sync, leading to new and exciting quantum behaviors.

Schäfer highlighted, "A lot of the physics we saw only happens because this is a continuous rather than a cyclic experiment. The most interesting lasing regime only appears when starting in a noisier state, and then slowly changing the cavity parameters to a less stable regime that is only upheld by the continuous lasing."

Cavity Frequency Pinning: Stabilizing the Quantum Orchestra

One of the challenges in maintaining continuous lasing and strong coupling is the sensitivity of the system to external disturbances. Any fluctuation in the cavity frequency can disrupt the delicate balance, much like a sudden noise can throw an orchestra off-key. To address this, the researchers discovered a new mechanism that pins or stabilizes the resonance frequency of the cavity. Schäfer notes, “[we] found out that without us even trying, this lasing mechanism stabilized the effective frequency of our cavity.”

Cavity frequency pinning involves stabilizing the frequency of the dressed cavity mode to match the frequency at which there is gain for light inside the cavity. This is achieved through an atomic loss mechanism that adjusts the number of atoms in the cavity based on the lasing intensity. When the cavity frequency drifts, the system automatically compensates by altering the atom number, keeping the cavity frequency and hence the lasing frequency stable.

"This gain mechanism also causes atom-heating which then causes a funny feedback loop that keeps the effective optical cavity frequency to a fixed value, even when we tried our darndest to change the cavity frequency," Thompson explained.

The Future is in Narrow Linewidths

The continuous lasing and strong collective coupling achieved in this study represent an important milestone in laser and quantum science. These advancements not only enhance our understanding of fundamental quantum interactions but also open the door to a wide range of practical applications.
Thompson shared their next steps, "Many different groups in atomic and laser physics are moving towards continuous rather than cyclical operation, whether it be for quantum computing or for ultranarrow linewidth lasers. We plan to really use the narrow linewidth transition in strontium to build incredibly single-color lasers to explore the world."

Soon, this technology could lead to the development of ultra-stable superradiant lasers with millihertz linewidths, which are crucial for high-precision measurements and tests of fundamental physics. Additionally, the techniques developed in this study could be applied to create new quantum sensors and devices that leverage the unique properties of continuous atom-cavity interactions. By orchestrating a tightly synchronized ensemble of atoms and light under conductor‑like control, researchers are not only pushing the boundaries of what’s possible but also laying the groundwork for the next generation of quantum technologies.

This research is supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Quantum Systems Accelerator, the National Science Foundation JILA Physics Frontier Center and Q-SEnSE QLCI, and the Humboldt Foundation.

In a groundbreaking study researchers at JILA have demonstrated continuous lasing and strong atom-cavity coupling using laser-cooled strontium atoms. This innovative experiment opens new avenues for precision measurement and quantum technologies, promising advancements in quantum sensing and metrology.

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