Research Highlights

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

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

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

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

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

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

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

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

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

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

Many quantum devices, from quantum sensors to quantum computers, use ions or charged atoms trapped with electric and magnetic fields as a hardware platform to process information. 

However, current trapped-ion systems face important challenges. Most experiments are limited to one-dimensional chains or two-dimensional planes of ions, which constrain the scalability and functionality of quantum devices. Scientists have long dreamed of stacking these ions into three-dimensional structures, but this has been very difficult because it’s hard to keep the ions stable and well-controlled when arranged in more complex ways.

To address these challenges, an international collaboration of physicists from India, Austria, and the USA—including JILA and NIST Fellow Ana Maria Rey, along with NIST scientists Allison Carter and John Bollinger—proposed that tweaking the electric fields that trap the ions can create stable, multilayered structures, opening up exciting new possibilities for future quantum technologies. The researchers published their findings in Physical Review X.
 

In the quiet halls of the Duane Physics building at the University of Colorado Boulder, two JILA researchers, postdoctoral research associate Catie LeDesma and graduate student Kendall Mehling, combine machine learning with atom interferometry to create the next generation of quantum sensors. Because these quantum sensors can be applied to various fields, from satellite navigation to measuring Earth’s composition, any advancement has major implications for numerous industries. 

As reported in a recent article preprint, the researchers successfully demonstrated how to build a quantum sensor using atoms moving through crystals made entirely of laser light. They applied accelerated forces to atoms along multiple directions and, using this sensor, measured the results, which closely matched values predicted by quantum theory. LeDesma and Mehling also showed that their device could accurately detect accelerations from just one run of their experiment, a feat that is very difficult to accomplish with traditional cold atom interferometry. 

JILA and NIST Fellow and University of Colorado Boulder Physics professor Jun Ye and his team at JILA, a collaboration between NIST and the University of Colorado Boulder, have developed an atomic clock of unprecedented precision and accuracy. This new clock uses an optical lattice to trap thousands of atoms with visible light waves, allowing for exact measurements. It promises vast improvements in fields such as space navigation, particle searches, and tests of fundamental theories like general relativity.

One of the biggest challenges in quantum technology and quantum sensing is “noise”–seemingly random environmental disturbances that can disrupt the delicate quantum states of qubits, the fundamental units of quantum information. Looking deeper at this issue, JILA Associate Fellow and University of Colorado Boulder Physics assistant professor Shuo Sun recently collaborated with Andrés Montoya-Castillo, assistant professor of chemistry (also at CU Boulder), and his team to develop a new method for better understanding and controlling this noise, potentially paving the way for significant advancements in quantum computing, sensing, and control. Their new method, which uses a mathematical technique called a Fourier transform, was published recently in the journal npj Quantum Information. 

In daily life, when two objects are “indistinguishable,” it’s due to an imperfect state of knowledge. As a street magician scrambles the cups and balls, you could, in principle, keep track of which ball is which as they are passed between the cups. However, at the smallest scales in nature, even the magician cannot tell one ball from another. True indistinguishability of this type can fundamentally alter how the balls behave. For example, in a classic experiment by Hong, Ou, and Mandel, two identical photons (balls) striking opposite sides of a half-reflective mirror are always found to exit from the same side of the mirror (in the same cup). This results from a special kind of interference, not any interaction between the photons. With more photons, and more mirrors, this interference becomes enormously complicated.

Measuring the pattern of photons that emerges from a given maze of mirrors is known as “boson sampling.” Boson sampling is believed to be infeasible to simulate on a classical computer for more than a few tens of photons. As a result, there has been a significant effort to perform such experiments with actual photons and demonstrate that a quantum device is performing a specific computational task that cannot be performed classically. This effort has culminated in recent claims of quantum advantage using photons.

Now, in a recently published Nature paper, JILA Fellow and NIST Physicist and University of Colorado Boulder Physics Professor Adam Kaufman and his team, along with collaborators at NIST (the National Institute of Standards and Technology), have demonstrated a novel method of boson sampling using ultracold atoms (specifically, bosonic atoms) in a two-dimensional optical lattice of intersecting laser beams. 

Dead stars known as white dwarfs, have a mass like the Sun while being similar in size to Earth. They are common in our galaxy, as 97% of stars are white dwarfs. As stars reach the end of their lives, their cores collapse into the dense ball of a white dwarf, making our galaxy seem like an ethereal graveyard. 

Despite their prevalence, the chemical makeup of these stellar remnants has been a conundrum for astronomers for years. The presence of heavy metal elements—like silicon, magnesium, and calcium—on the surface of many of these compact objects is a perplexing discovery that defies our expectations of stellar behavior. 

“We know that if these heavy metals are present on the surface of the white dwarf, the white dwarf is dense enough that these heavy metals should very quickly sink toward the core,” explains JILA graduate student Tatsuya Akiba. “So, you shouldn't see any metals on the surface of a white dwarf unless the white dwarf is actively eating something.” 

While white dwarfs can consume various nearby objects, such as comets or asteroids (known as planetesimals), the intricacies of this process have yet to be fully explored. However, this behavior could hold the key to unraveling the mystery of a white dwarf's metal composition, potentially leading to exciting revelations about white dwarf dynamics. 

In results reported in a new paper in The Astrophysical Journal Letters, Akiba, along with JILA Fellow and University of Colorado Boulder Astrophysical and Planetary Sciences professor Ann-Marie Madigan and undergraduate student Selah McIntyre, believe they have found a reason why these stellar zombies eat their nearby planetesimals. Using computer simulations, the researchers simulated the white dwarf receiving a “natal kick” during its formation (which has been observed) caused by asymmetric mass loss, altering its motion and the dynamics of any surrounding material. 

Precisely measuring the energy states of individual atoms has been a historical challenge for physicists due to atomic recoil. When an atom interacts with a photon, the atom “recoils” in the opposite direction, making it difficult to measure the position and momentum of the atom precisely. This recoil can have big implications for quantum sensing, which detects minute changes in parameters, for example, using changes in gravitational waves to determine the shape of the Earth or even detect dark matter. 

In a new paper published in Science, JILA and NIST Fellows Ana Maria Rey and James Thompson, JILA Fellow Murray Holland, and their teams proposed a way to overcome this atomic recoil by demonstrating a new type of atomic interaction called momentum-exchange interaction, where atoms exchanged their momentums by exchanging corresponding photons. 

Using a cavity—an enclosed space composed of mirrors—the researchers observed that the atomic recoil was dampened by atoms exchanging energy states within the confined space. This process created a collective absorption of energy and dispersed the recoil among the entire population of particles.

While it may not look like it, the interstellar space between stars is far from empty. Atoms, ions, molecules, and more reside in this ethereal environment known as the Interstellar Medium (ISM). The ISM has fascinated scientists for decades, as at least 200 unique molecules form in its cold, low-pressure environment. It’s a subject that ties together the fields of chemistry, physics, and astronomy, as scientists from each field work to determine what types of chemical reactions happen there. 

Now, in the recently published cover article of the Journal of Physical Chemistry A, JILA Fellow and University of Colorado Boulder Physics Professor Heather Lewandowski and former JILA graduate student Olivia Krohn highlight their work to mimic ISM conditions by using Coulomb crystals, a cold pseudo-crystalline structure, to watch ions and neutral molecules interact with each other. 

While atomic clocks are already the most precise timekeeping devices in the universe, physicists are working hard to improve their accuracy even further. One way is by leveraging spin-squeezed states in clock atoms. Spin-squeezed states are entangled states in which particles in the system conspire to cancel their intrinsic quantum noise. These states, therefore, offer great opportunities for quantum-enhanced metrology since they allow for more precise measurements. Yet, spin-squeezed states in the desired optical transitions with little outside noise have been hard to prepare and maintain. 

One particular way to generate a spin-squeezed state, or squeezing, is by placing the clock atoms into an optical cavity, a set of mirrors where light can bounce back and forth many times. In the cavity, atoms can synchronize their photon emissions and emit a burst of light far brighter than from any one atom alone, a phenomenon referred to as superradiance. Depending on how superradiance is used, it can lead to entanglement, or alternatively, it can instead disrupt the desired quantum state. 

In a prior study, done in a collaboration between JILA and NIST Fellows, Ana Maria Rey and James Thompson, the researchers discovered that multilevel atoms (with more than two internal energy states) offer unique opportunities to harness superradiant emission by instead inducing the atoms to cancel each other’s emissions and remain dark. 

Now, reported in a pair of new papers published in Physical Review Letters and Physical Review A, Rey and her team discovered a method for how to not only create dark states in a cavity, but more importantly, make these states spin squeezed. Their findings could open remarkable opportunities for generating entangled clocks, which could push the frontier of quantum metrology in a fascinating way. 

Astronomers have long sought to understand the early universe, and thanks to the James Webb Space Telescope (JWST), a critical piece of the puzzle has emerged. The telescope's infrared detecting “eyes” have spotted an array of small, red dots, identified as some of the earliest galaxies formed in the universe. 

This surprising discovery is not just a visual marvel, it's a clue that could unlock the secrets of how galaxies and their enigmatic black holes began their cosmic journey.
“The astonishing discovery from James Webb is that not only does the universe have these very compact and infrared bright objects, but they're probably regions where huge black holes already exist,” explains JILA Fellow and University of Colorado Boulder astrophysics professor Mitch Begelman. “That was thought to be impossible.” 

Begelman and a team of other astronomers, including Joe Silk, a professor of astronomy at Johns Hopkins University, published their findings in The Astrophysical Journal Letters, suggesting that new theories of galactic creation are needed to explain the existence of these huge black holes. 

When it comes to drug development, membrane proteins play a crucial role, with about 50% of drugs targeting these molecules. Understanding the function of these membrane proteins, which connect to the membranes of cells, is important for designing the next line of powerful drugs. To do this, scientists study model proteins, such as bacteriorhodopsin (bR), which, when triggered by light, pump protons across the membrane of cells. 

While bR has been studied for half a century, physicists have recently developed techniques to observe its folding mechanisms and energetics in the native environment of the cell’s lipid bilayer membrane. In a new study published by Proceedings of the National Academy of Sciences (PNAS), JILA and NIST Fellow Thomas Perkins and his team advanced these methods by combining atomic force microscopy (AFM), a conventional nanoscience measurement tool, with precisely timed light triggers to study the functionality of the protein function in real-time. 

In a new study published in Science today, JILA and NIST (National Institute of Standards and Technology) Fellow and University of Colorado Boulder physics professor Jun Ye and his research team have taken a significant step in understanding the intricate and collective light-atom interactions within atomic clocks, the most precise clocks in the universe. 

In physics, scientists have been fascinated by the mysterious behavior of superconductors—materials that can conduct electricity with zero resistance when cooled to extremely low temperatures. Within these superconducting systems, electrons team up in “Cooper pairs” because they're attracted to each other due to vibrations in the material called phonons. 

As a thermodynamic phase of matter, superconductors typically exist in an equilibrium state. But recently, researchers at JILA became interested in kicking these materials into excited states and exploring the ensuing dynamics. As reported in a new Nature paper, the theory and experiment teams of JILA and NIST Fellows Ana Maria Rey and James K. Thompson, in collaboration with Prof. Robert Lewis-Swan at the University of Oklahoma, simulated superconductivity under such excited conditions using an atom-cavity system. 

Within atomic and laser physics communities, scientist John “Jan” Hall is a key figure in the history of laser frequency stabilization and precision measurement using lasers. Hall's work revolved around understanding and manipulating stable lasers in ways that were revolutionary for their time. His work laid a technical foundation for measuring a tiny fractional distance change brought by a passing gravitational wave. His work in laser arrays awarded him the Nobel Prize in Physics in 2005. 

Building on this foundation, JILA and NIST Fellow Jun Ye and his team embarked on an ambitious journey to push the boundaries of precision measurement even further. This time, their focus turned to a specialized technique known as the Pound-Drever-Hall (PDH) method (developed by scientists R. V. Pound, Ronald Drever, and Jan Hall himself), which plays a large role in precision optical interferometry and laser frequency stabilization.

While physicists have used the PDH method for decades in ensuring their laser frequency is stably “locked” to an artificial or quantum reference, a limitation arising from the frequency modulation process itself, called residual amplitude modulation (RAM), can still affect the stability and accuracy of the laser’s measurements. 

In a new Optica paper, Ye’s team, working with JILA electronic staff member Ivan Ryger and Hall, describe implementing a new approach for the PDH method, reducing RAM to never-before-seen minimal levels while simultaneously making the system more robust and simpler. 

Historically, JILA (a joint institute established by the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder) has been a world leader in precision timekeeping using optical atomic clocks. These clocks harness the intrinsic properties of atoms to measure time with unparalleled precision and accuracy, representing a significant leap in our quest to quantify the most elusive of dimensions: time.

However, the precision of these clocks has fundamental limits, including the “noise floor,” which is affected by the “quantum projection noise” (QPN). “This comes from the spin-statistics of the individual qubits, the truly quantum nature of the atoms being probed,” elaborated JILA graduate student Maya Miklos. State-of-the-art clock comparisons, like those directed by JILA and NIST Fellow and University of Colorado Boulder Physics professor Jun Ye, are pushing ever closer to this fundamental noise floor limit. However, this limit can be circumvented by generating quantum entanglement in the atomic samples, boosting their stability.

Now, Ye’s team, in collaboration with JILA and NIST Fellow James K. Thompson, has used a specific process known as spin squeezing to generate quantum entanglement, resulting in an enhancement in clock performance operating at the 10-17stability level. Their novel experimental setup, published in Nature Physics, also allowed the researchers to directly compare two independent spin-squeezed ensembles to understand this level of precision in time measurement, a level never before reached with a spin-squeezed optical lattice clock. 

In a new study published in Scientific Reports, JILA Fellow and University of Colorado Boulder physics professor Andreas Becker and his team theorized a new method to produce extreme ultraviolet (EUV) and x-ray light with elliptical polarization, a special shape in which the direction of light waves’ oscillation is changing. This method could provide experimentalists with a simple technique to generate such light, which is beneficial for physicists to further understand the interactions between electrons in materials on the quantum level, paving the way for designing better electronic devices such as circuit boards, solar panels, and more.