Research Highlights

Deep within every piece of magnetic material, electrons dance to the invisible tune of quantum mechanics. Their spins, akin to tiny atomic tops, dictate the magnetic behavior of the material they inhabit. This microscopic ballet is the cornerstone of magnetic phenomena, and it's these spins that a team of JILA researchers—headed by JILA Fellows and University of Colorado Boulder physics professors Margaret Murnane and Henry Kapteyn—has learned to control with remarkable precision, potentially redefining the future of electronics and data storage. 

As reported in a new Science Advances paper, the JILA team and collaborators from universities in Sweden, Greece, and Germany probed the spin dynamics within a special material known as a Heusler compound: a mixture of metals that behaves like a single magnetic material. For this study, the researchers utilized a compound of cobalt, manganese, and gallium, which behaved as a conductor for electrons whose spins were aligned upwards and as an insulator for electrons whose spins were aligned downwards.

Using a form of light called extreme ultraviolet high-harmonic generation (EUV HHG) as a probe, the researchers could track the re-orientations of the spins inside the compound after exciting it with a femtosecond laser, which caused the sample to change its magnetic properties. The key to accurately interpreting the spin re-orientations was the ability to tune the color of the EUV HHG probe light.
“In the past, people haven't done this color tuning of HHG,” explained co-first author and JILA graduate student Sinéad Ryan. “Usually, scientists only measured the signal at a few different colors, maybe one or two per magnetic element at most.” In a historic first, the JILA team tuned their EUV HHG light probe across the magnetic resonances of each element within the compound to track the spin changes with a precision down to femtoseconds (a quadrillionth of a second).

“On top of that, we also changed the laser excitation fluence, so we were changing how much power we used to manipulate the spins,” Ryan elaborated, highlighting that that step was also an experimental first for this type of research. By changing the power, the researchers could influence the spin changes within the compound.

When measuring minor changes for quantities like forces, magnetic fields, masses of small particles, or even gravitational waves, physicists use micro-mechanical resonators, which act like tuning forks, resonating at specific frequencies. Traditionally, it was assumed that the temperature across these devices is uniform. 

However, new research from JILA Fellow and University of Colorado Boulder physics professor Cindy Regal and her team, Dr. Ravid Shaniv and graduate student Chris Reetz has found that in specific scenarios, such as advanced studies looking at the interactions between light and mechanical objects, where the temperature might differ in various resonator parts, which lead to unexpected behaviors. Their observations, published in Physical Review Research, can potentially revolutionize the design of micro-mechanical resonators for quantum technology and precision sensing.

Quantum sensors help physicists understand the world better by measuring time passage, gravity fluctuations, and other effects at the tiniest scales. For example,  one quantum sensor, the LIGO gravitational wave detector, uses quantum entanglement (or the interdependence of quantum states between particles) within a laser beam to detect distance changes in gravitational waves up to one thousand times smaller than the width of a proton! 

LIGO isn’t the only quantum sensor harnessing the power of quantum entanglement. This is because entangled particles are generally more sensitive to specific parameters, giving more accurate measurements. 

While researchers can generate entanglement between particles, the entanglement may only be useful sometimes for sensing something of interest. To measure the “usefulness” of quantum entanglement for quantum sensing, physicists calculate a mathematical value, known as the Quantum Fisher Information (QFI), for their system. However, physicists have found that the more quantum states in the system, the harder it becomes to determine which QFI to calculate for each state. 

To overcome this challenge, JILA Fellow Murray Holland and his research team proposed an algorithm that uses the Quantum Fisher Information Matrix (QFIM), a set of mathematical values that can determine the usefulness of entangled states in a complicated system. 

Their results, published in Physical Review Letters as an Editor’s Suggestion, could offer significant benefits in developing the next generation of quantum sensors by acting as a type of “shortcut” to find the best measurements without needing a complicated model.

In quantum information science, many particles can act as “bits,” from individual atoms to photons. At JILA, researchers utilize these bits as “qubits,” storing and processing quantum 1s or 0s through a unique system. 

While many JILA Fellows focus on qubits found in nature, such as atoms and ions, JILA Associate Fellow and University of Colorado Boulder Assistant Professor of Physics Shuo Sun is taking a different approach by using “artificial atoms,” or semiconducting nanocrystals with unique electronic properties. By exploiting the atomic dynamics inside fabricated diamond crystals, physicists like Sun can produce a new type of qubit, known as a “solid-state qubit,” or an artificial atom.

To study nanoscale patterns in tiny electronic or photonic components, a new method based on lensless imaging allows for near-perfect high-resolution microscopy. This is especially important at wavelengths shorter than ultraviolet, which can image with higher spatial resolution than visible light but where image-forming optics are imperfect. 

The most powerful form of lensless imaging is called ptychography, which works by scanning a laser-like beam across a sample, collecting the scattered light, and then using a computer algorithm to reconstruct an image of the sample. 

While ptychography can visualize many nanostructures, this special microscope has trouble analyzing samples with very regular, repeating patterns. This is because the scattered light does not change as a periodic sample is scanned, so the computer algorithm gets confused and cannot reconstruct a good image.

Taking on this challenge, recently graduated Ph.D. researchers Bin Wang and Nathan Brooks, working with JILA Fellows Margaret Murnane and Henry Kapteyn, developed a novel method that uses short-wavelength light with a special vortex or donut shape to scan these repeating surfaces, resulting in more varied diffraction patterns. This allowed the researchers to capture high-fidelity image reconstructions using this new approach, which they recently published in Optica. This result will also be highlighted in the Optica Magazine Optics and Photonics News in the annual highlights of Optics in 2023. 

Opening new possibilities for quantum sensors, atomic clocks and tests of fundamental physics, JILA researchers have developed new ways of “entangling” or interlinking the properties of large numbers of particles. In the process they have devised ways to measure large groups of atoms more accurately even in disruptive, noisy environments. 

The new techniques are described in a pair of papers published in Nature. JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder. 

To engineer materials with unique properties, like superconductivity, scientists dive into the quantum interactions between electrons and vibrational particles called phonons. When electrons and phonons strongly interact, they behave as “quasi” particles, not single isolated particles. These interactions occur on extremely short timescales: electrons interact with each other in femtoseconds (10^-15 seconds) or even faster, while phonons respond more slowly, within hundreds of femtoseconds, since the heavier atoms move more slowly than electrons. 

To investigate these interactions, scientists often change a material's temperature, pressure, or chemical composition and measure its electrical properties to learn about the interactions. However, materials that host different interactions can exhibit very similar properties, making it challenging to pinpoint the exact nature of these interactions.

To overcome this issue, JILA graduate student Yingchao Zhang, working with JILA Fellows Henry Kapteyn and Margaret Murnane and University of Colorado Boulder physics professor Rahul Nandkishore, utilized a powerful new method to precisely identify phonon interactions within quantum materials, the results of which were published in Nano Letters. Using ultraprecise, timed laser pulses, and extreme ultraviolet pulses, they measured the response times and saw precisely how the electrons and phonons interacted.  This method paves the way for better control and manipulation of quantum materials.

In a new paper in The Astrophysical Journal, JILA Fellow Jason Dexter, graduate student Kirk Long, and other collaborators compared two main theoretical models for emission data for a specific quasar, 3C 273. Using these theoretical models, astrophysicists like Dexter can better understand how these quasars form and change over time.

Quasars, or active galactic nuclei (AGN), are believed to be powered by supermassive black holes at their centers. Among the brightest objects in the universe, quasars emit a brilliant array of light across the electromagnetic spectrum. This emission carries vital information about the nature of the black hole and surrounding regions, providing clues that astrophysicists can exploit to better understand the black hole's dynamics. 

In a recent Science paper, researchers led by JILA and NIST Fellow Jun Ye, along with collaborators JILA and NIST Fellow David Nesbitt, scientists from the University of Nevada, Reno, and Harvard University, observed novel ergodicity-breaking in C60, a highly symmetric molecule composed of 60 carbon atoms arranged on the vertices of a “soccer ball” pattern (with 20 hexagon faces and 12 pentagon faces). Their results revealed ergodicity breaking in the rotations of C60. Remarkably, they found that this ergodicity breaking occurs without symmetry breaking and can even turn on and off as the molecule spins faster and faster. Understanding ergodicity breaking can help scientists design better-optimized materials for energy and heat transfer. 

Many everyday systems exhibit “ergodicity” such as heat spreading across a frying pan and smoke filling a room. In other words, matter or energy spreads evenly over time to all system parts as energy conservation allows. On the other hand, understanding how systems can violate (or “break”) ergodicity, such as magnets or superconductors, helps scientists understand and engineer other exotic states of matter.

In a new ACS Nano paper, JILA and NIST Fellow David Nesbitt, along with former graduate student Jacob Pettine and other collaborators, developed a new method for measuring the dynamics of specific particles known as “hot carriers,” as a function of both time and energy, unveiling detailed information that can be used to improve collection efficiencies.

Metal ions can be found in almost every environment, including wastewater, chemical waste and electronic recycling waste. Properly recovering and recycling valuable metals from various sources is crucial for sustainable resource management and contributes to environmental cleanup. Because of the scarcity of some of these metals, such as rare earth elements or nickel, scientists are working to find ways to remove these ions from the waste and recycle the metals. One method used to remove these metals is to bind them to other molecules known as chelators or chelating agents. Chelators have multiple molecular groups that combine to form binding sites with a natural affinity for binding metal ions, making them a natural choice to extract metals from toxic waste. Ethylenediaminetetraacetic acid, or EDTA, is a chelator commonly used in metal removal and many other applications, including medicine. “EDTA is used to treat heavy-metal poisoning,” JILA graduate student Lane Terry explained. “So, if you have lead poisoning, you can take EDTA, which binds to the lead and then safely passes through your system. It's also used as a food preservative. So EDTA is everywhere. It's in one of my topical creams, etc.” EDTA is also commonly used in various laboratories, including many within JILA. 

To understand how EDTA binds to these metal ions and water molecules, Madison Foreman, a former JILA graduate student in the Weber group, now a postdoctoral researcher at the University of California, Berkeley, Terry, and their supervisor, JILA Fellow J. Mathias Weber, studied the geometry of the EDTA binding site using a unique method that helped to isolate the molecules and their bound ions, allowing for more in-depth analyses of the binding interactions. They published a series of three papers on this topic. In their first paper, published in the Journal of Physical Chemistry A, they found that the size of the metal ion changes where it sits in the EDTA binding site, which affects other binding interactions, especially with water. 

Some of the biggest questions about our universe may be solved by scientists using its tiniest particles. Since the 1960s, physicists have been looking at particle interactions to understand an observed imbalance of matter and antimatter in the universe. Much of the work has focused on interactions that violate charge and parity (CP) symmetry. This symmetry refers to a lack of change in our universe if all particles’ charges and orientations were inverted. “This charge and parity symmetry is the symmetry that high-energy physicists say needs to be violated to result in this imbalance between matter and antimatter,” explained JILA research associate Luke Caldwell. To try to find evidence of this violation of CP symmetry, JILA and NIST Fellows Jun Ye and Eric Cornell, and their teams, including Caldwell, collaborated to measure the electron electric dipole moment (eEDM), which is often used as a proxy measure for the CP symmetry violation. The eEDM is an asymmetric distortion of the electron’s charge distribution along the axis of its spin. To try to measure this distortion, the researchers used a complex setup of lasers and a novel ion trap. Their results, published in Science as the cover story and Physical Review A, leveraged a longer experiment time to improve the precision measurement by a factor of 2.4, setting new records. 

Quantum materials, a fascinating class of materials that harness the power of quantum mechanics, are revolutionizing modern science and technology. Quantum materials often possess exotic states of matter, such as superconductivity or magnetic ordering, that defy conventional understanding and can be manipulated for various technological applications. To further enhance and manipulate the intriguing characteristics of quantum materials, researchers leverage nanostructuring—the ability to precisely control the geometry on the atomic scale. Specifically, nanostructuring provides the ability to manipulate and fine-tune the electrical and thermal properties of quantum and other materials. This can result, for example, in designer structures that conduct current very well, but impede heat transport. A related critical challenge for a broad range of nanotechnologies is the need for more efficient cooling so that the nanodevices do not overheat during operation. To better understand heat transport at the nanoscale, JILA Fellows Margaret Murnane, Henry Kapteyn, and their research groups within the STROBE NSF Center, JILA, and the University of Colorado Boulder, created the first general analytical theory of nanoscale-confined heat transport, that can be used to engineer heat transport in 3D nanosystems—such as nanowires and nanomeshes—that are of great interest for next-generation energy-efficient devices. This discovery was published in NanoLetters. 

Two-dimensional materials, like graphene and 2D semiconductors, are an area of physics that has been growing tremendously in the last decade. According to JILA graduate student Ben Whetten, “That’s because they exhibit new spin and electronic physical phenomena and have much promise to build new miniaturized photonic or semiconductor nanoscale devices.” Researchers like Whetten, and his advisor, JILA Fellow, and University of Colorado Boulder professor Markus Raschke, develop methods to image these materials, giving a better understanding of their inner workings. In a new paper in NanoLetters, Raschke, and his team extended their ultrafast microscope to see nanometer-sized imperfection(s) within a 2D semiconductor sample that created some surprising nonlinear optical effects. 

The best clock in the world has no hands, no pendulum, no face or digital display. It is made of ultra-cold atoms trapped by light.  This atomic clock is so precise that, had it begun ticking when Earth formed billions of years ago, it would not yet have gained or lost a second. Nonetheless, this incredible clock, and all atomic clocks, operate with collections of independent atoms, and as a result, their precision is limited by the fundamental laws of quantum mechanics.  One way to get around this fundamental quantum imprecision is to entangle the atoms, or make them talk, in such a way that one cannot describe the individual atoms’ quantum states independently of one another. In this case it is possible to create the situation where the quantum noise of one atom in the clock 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. One type of entangled state is called a “squeezed state”, which can be visualized as if one had shaped the quantum noise in a way that is narrower in one direction at the expense of making the fuzziness in the adjacent direction worse.  Squeezed states have been realized in several labs around the world at groundbreaking precision levels recorded by several physics institutes, including  at JILA in Boulder, Colorado.  However, squeezing is experimentally challenging to create and there is a need for a variety of “flavors” of squeezing for different types of quantum sensing tasks.

A new approach recently described in Physical Review Letters explores a new way to generate squeezing that is exponentially faster than previous experiments and generates a new flavor of entanglement:  two-mode squeezing—a type of entanglement that is thought to be used for improving the best atomic clocks and for sensing how gravity changes the flow of time. This promising new approach was developed by a collaboration of JILA and NIST Fellows Ana Maria Rey and James K. Thompson, and their team members, along with Bhuvanesh Sundar, a former postdoctoral researcher at JILA now at Rigetti Computing, and former JILA research associate Dr. Robert Lewis-Swan, now an Assistant Professor at the University of Oklahoma.

Although one might think it would be simple, the genetics of bacteria can be rather complicated. A bacterium’s genes use a set of regulatory proteins and other molecules to monitor and change genetic expressions within the organism. One such mechanism is the riboswitch, a small piece of RNA that can turn a gene “on” or “off.” In order to “flip” this genetic switch, a riboswitch must bind to a specific ion or molecule, called a ligand, at a special riboswitch site called the aptamer. The ligand either activates the riboswitch (allowing it to regulate gene expression) or inactivates it until the ligand unbinds and leaves the aptamer. Understanding the relationship between ligands and aptamers can have big implications for many fields, including healthcare.  “Understanding riboswitches and gene expression can help us develop better antimicrobial drugs,” explained JILA graduate student Andrea Marton Menendez. “The more we know about how to attack bacteria, the better, and if we can just target one small interaction that prevents or abets a gene from being translated or transcribed, we may have an easier way to treat bacterial infections.”  
To better understand the dynamics of aptamer and ligand binding, Marton Menendez, along with JILA and NIST Fellow David Nesbitt, looked at the lysine (an amino acid) riboswitch in Bacillus subtilis, a common type of bacterium present in environments ranging from cow stomachs to deep sea hydrothermal vents. With this model organism, the researchers studied how different secondary ligands, like, potassium, cesium, and sodium, affect riboswitch activation, or its physical folding. The results have been published in the Journal of Physical Chemistry B.

For a new study, a team of physicists recruited roughly 1,000 undergraduate students at CU Boulder to help answer one of the most enduring questions about the sun: How does the star’s outermost atmosphere, or “corona,” get so hot?

The research represents a nearly-unprecedented feat of data analysis: From 2020 to 2022, the small army of mostly first- and second-year students examined the physics of more than 600 real solar flares—gigantic eruptions of energy from the sun’s roiling corona. 

The researchers, partially lead by JILA fellow Heather Lewandowski, and including 995 undergraduate and graduate students, published their finding May 9 in The Astrophysical Journal. The results suggest that solar flares may not be responsible for superheating the sun’s corona, as a popular theory in astrophysics suggests. 
 

Dipolar gases have become an increasingly important topic in the field of quantum physics in recent years. These gases consist of atoms or molecules that possess a non-zero electric dipole moment, which gives rise to long-range dipole-dipole interactions between particles. These interactions can lead to a variety of interesting and exotic quantum phenomena that are not observed in conventional gases. 

For decades, black holes have fascinated scientists and nonscientists alike. Their ominous voids, like an open pair of jaws, has inspired a whole wave of science-fiction featuring the phenomenon. Physicists have also been similarly inspired, specifically to understand the dynamics of what is happening inside of the black hole, especially for objects thatmay fall in. The historical theories about black holes are closely linked to those within quantum physics and they suggest interesting phenomena. “The best models of black holes we have in general relativity, like the Kerr metric or the Reissner-Nordström metric, actually make some pretty crazy predictions,” explained JILA graduate student Tyler McMaken. “After you fall in, you eventually reach a spot, called the inner horizon, where we can enter into a wormhole, see a naked singularity [A region in space-time at which matter is infinitely dense], time-travel, and do a bunch of things that go against what we think should be physically possible.” To better understand the quantum mechanics of these black hole models, McMaken and JILA Fellow Andrew Hamilton and looked into the quantum effects that may be happening around and inside a black hole. From their research, they found that there was a divergence of energy into multiple levels at the inner horizon of the black hole, suggesting that quantum effects play a crucial role in how to model realistic black holes. “The exciting part of this research is the discovery that quantum effects save the day—as you approach the inner horizon, you're met with a wall of diverging energy from Hawking radiation, so that any weird, causality-violating parts of the spacetime are completely blocked off and replaced with a singularity,” McMaken added. This diverging energy split the radiation into multiple levels. “Without a full theory of quantum gravity, we won’t know exactly what happens at this singularity, but we do know that just like the Big Bang singularity, or the singularity we might find in simpler spherical black holes, it marks the end of spacetime as we know it as the curvature exceeds the Planck scale.” The results of the study have been submitted by McMaken and Hamilton for publication in the journal Physical Review D.

JILA researchers have upgraded a breathalyzer based on Nobel Prize-winning frequency-comb technology and combined it with machine learning to detect SARS-CoV-2 infection in 170 volunteer subjects with excellent accuracy. Their achievement represents the first real-world test of the technology’s capability to diagnose disease in exhaled human breath.