Nathan Schine Twists Photons and Cools Atoms in a Unique Quantum Dance

Deepening our understanding of the quantum world and developing new tools to peer into it is a very active area of physics research today. In this crowded field full of diverse theoretical ideas and physical tools, Assistant Professor and JQI Fellow Nathan Schine has managed to carve out a distinctive space for himself and his lab.Nathan SchineNathan Schine

Schine’s research program manipulates the interactions between atoms and photons—the particles that make up light—in novel, well-controlled ways in order to simulate other, harder-to-probe quantum phenomena. To coax the photons into new simulation patterns, Schine is using unique arrangements of mirrors to bounce photons around. He is also strategically placing atoms in the photons’ way with the help of precisely controlled laser beams. To boot, the atoms he is using (ytterbium) have a relatively complex structure, giving Schine extra avenues to explore. He has been able to create this unique niche by combining the experimental expertise he gained from graduate school and postdoctoral research with his theoretical big-picture savvy.

Schine has been slowly homing in on his academic sweet spot for much of his life. Growing up, his interests were broad—they included science and math, but also history and other areas of the humanities. “It wasn't like I knew from an early age that I was going to go be a physicist,” Schine says.

Science wasn’t outside the realm of Schine’s imagination, however. His father was a chemistry teacher, his mother had a degree in math, and his grandfather was a physics professor at Vanderbilt University. 

Keeping his options open, Schine attended Williams College. Ranked first among U.S. liberal arts colleges by U.S. News and World Report, Williams boasts an unusually strong science and math program. Schine was interested in math, but eventually found it to be too abstract for his taste. “When math got into proving the existence of a solution to a problem and not actually solving the problem, I sort of lost the thread a bit,” he recalls. Instead, he found that the part of math he enjoyed most could be gotten through physics, so he dove deeper into the subject. 

An undergraduate research project sealed the deal for Schine as a physicist and experimentalist. He started working in the lab of his soon-to-be quantum mechanics professor, Barclay Jermain Professor of Natural Philosophy at Williams Protik Majumder, midway through his sophomore year.

Under Majumder’s supervision, Schine started to get a taste for experimental physics. He was performing spectroscopic measurements on indium atoms as a sophomore and continued working with Majumder until he graduated. Indium, with its three loosely bound, outermost electrons, is hard to model theoretically, and Majumder’s lab collaborated with theorists to benchmark their calculations and zero in on precise values. 

Schine relished the chance to make a real contribution to the project. He also found joy in tinkering in the lab, finding his calling as an experimentalist. “I liked the day-to-day aspects of it, the actual process of building a laser or something,” Schine says. “A lot of it is very tactile and building up this sort of Rube Goldberg device that happens to be useful for physics—that, I think, is a lot of fun.”

Majumder had a slightly different take on what set Schine apart in his lab. “He was really unusual, even as a 20-year-old, in being able to balance comfortably the very hands-on build stuff with the bigger intellectual picture, which is obviously something that's been characteristic of his career since then,” Majumder says. Schine’s research with Majumder culminated in a senior thesis and a peer-reviewed publication

Schine was inspired by his undergraduate research experience and decided to pursue graduate school. His chops setting up lasers and other experimental equipment meant he could hit the ground running and start contributing right away to the brand-new lab of Jonathan Simon at the University of Chicago. 

The lab Simon was envisioning involved filling an optical cavity—a set of mirrors trapping light and bouncing it back and forth between them—with ultracold rubidium atoms. The idea was to use the photons themselves as a quantum playground, used to re-create and study quantum phenomena that happen in other, less accessible settings. 

A lot of the interesting quantum phenomena that appear in real materials are hard to peer into at the quantum level but are nevertheless important for our daily lives because of their ubiquitous applications in technology. In Simon’s lab, precisely controlled photons can play a similar role to electrons inside of a material. Studying how these photons behave in a cavity and measuring them directly can then give clues about what happens inside the chunks of material. 

There is one obvious limitation for photons playing the part of electrons: They don’t have an electric charge. And charged electrons—specifically in magnetic fields—are responsible for a range of interesting material effects that might need simulating. 

Back in the early 1980s, physicists discovered one such effect.  A thin layer of semiconductor placed inside a strong magnetic field was found to conduct electricity in very precise chunks. As the magnetic field is increased, the conductivity doesn’t change for a while—it stays at one plateau—and then hops abruptly to another plateau. This is known as the integer quantum Hall effect (IQHE) because the plateaus appeared at very regularly spaced integer values.

Even more strangely, for very cleanly engineered semiconductors, experimentalists found sub-plateaus within the plateaus, appearing at precise fractions of the previous integer values. They termed this, predictably, the fractional quantum Hall effect (FQHE). The origins of these fractional plateaus are largely still a mystery, although physicists are pretty certain that it has something to do with interactions between electrons giving rise to unexpected collective behaviors. If there was a way to simulate the full quantum theory of the FQHE, it might reveal new insights into what’s going on. 

Simon and Schine, along with their labmates, hatched a plan. They conceived of a new way to make photons behave as though they have charge and live in a magnetic field that could, in principle, allow the photons to interact with each other and simulate the FQHE. Their plan involved a wonky cavity: four mirrors aligned to bounce light around in a twisted bow-tie configuration over and over again, with one of the mirrors slightly askew, as in the diagram shown below.

Photons and atoms in Schine’s tilted bow-tie cavity. (Credit: Nathan Schine/JQI)Photons and atoms in Schine’s tilted bow-tie cavity. (Credit: Nathan Schine/JQI)

Schine and his labmates focused on what happened along a plane at the center of this cavity. There, the photons were analogous to electrons traveling inside a thin material like in either of the Hall effects. The twisted mirror configuration causes the photons to twist around, much like electrons precess around inside a magnetic field. 

With careful cavity design, they were able to make the analogy come to life and make their photons replicate the IQHE in its full glory. They published this result in the journal Nature

To go beyond integer quantum Hall physics, the particles need to interact with one another—not just pass through each other, like photons are wont to do. That’s where atoms entered the picture. Previously, scientists had worked out a technique that allows atoms to serve as an intermediary through which photons can talk to each other. 

In parallel with the twisted cavity work, Simon’s lab had been working on this atom-assisted approach to making photons interact with each other. This involved cooling a gas of rubidium atoms to extremely low temperatures, just a touch above absolute zero. Then, the light was tuned to a particular color that would allow one of the rubidium atoms to absorb a single photon. This atom then prevented any nearby atoms from absorbing a photon, ensuring no other photon got too close. This created an effective interaction between photons, where they were averse to being too close to one another. 

The next step was to combine the two techniques: put the rubidium inside the skewed bowtie cavity. The cavity makes photons act like electrons in a magnetic field, and the atoms create a medium through which the photons can interact. The combination created the right conditions for FQHE physics. Although short-lived, the photons in Schine’s experiment appeared to indeed exhibit the hallmarks of fractional quantum Hall physics. Schine and his labmates published this result in the journal Nature

This was the first time the fractional quantum Hall effect had been simulated in any medium. For his graduate work, Schine was named a finalist for a thesis prize from the American Physical Society’s Division of Atomic Molecular and Optical Physics, the most prestigious thesis award in this field. 

Schine was still circling around his ultimate niche, though, and he sought to broaden his experimental skillset during his postdoctoral studies. He joined the group of Adam Kaufman at JILA at the University of Colorado Boulder (sometimes snarkily called JQI West). Kaufman’s lab manipulates atoms with light, using a tool called optical tweezers—laser beams focused down to a very narrow spot, intense enough to hold an atom in place. 

Schine, Kaufman, and collaborators used these optical tweezers to put a new spin on atomic clocks, which are the most precise timekeepers we have. They work by counting the intrinsic ticking of individual atoms. Precise as they are, scientists are actively working on making them even more so, both for better technology like navigation and geolocation and for scientific inquiries, like the basic nature of fundamental constants and gravity

The team endeavored to use a fundamentally quantum property—entanglement—to make pairs of atoms tick in tandem, thereby making the clock more precise. They cooled a gas of strontium atoms just above absolute zero and used optical tweezers to create a large array of atom pairs. These pairs were then made to interact using the same trick Schine had used during his graduate work: one atom absorbing a photon prevented another atom nearby from doing so as well, thus making their behavior depend on one another. Generating entangled atoms like this is a promising way to improve clock performance. They published this work in the journal Nature Physics

Now, Schine is starting to build up his own lab here at the University of Maryland. When deciding exactly what kind of experiment to embark upon, Schine was guided by his graduate school advisor Simon’s philosophy. “There are different strategies for setting up experiments,” Schine says. “But I think Jon’s was very much to build something that no one else has done before experimentally—to put ourselves in an area where there's a lot of low-hanging fruit.” Schine explained that this will involve combining his optical cavity expertise with an array of tweezer-trapped atoms, now using ytterbium. For instance, he predicts this will allow dramatic improvements in performing quantum measurements, which is an essential part of quantum computing or quantum simulation experiments. 

As Schine is assembling his lab and unique research program, he encourages interested students and postdocs to reach out to him. And, according to Schine’s undergraduate adviser, Schine’s teaching and mentoring abilities promise to be excellent. “One of the things we really work hard at in a place like Williams,” Majumder says, “is to make sure our students are not just the ones who can get into the lab, hide in a corner and just do amazing work. And that really comes through with Nathan. He's just such a good explainer of what he's doing. And he's so enthusiastic—it's very infectious.”

Story by Dina Genkina

Alum Jonathan Hoffman Heads Toward New Horizon in Navigation Science

As a PhD graduation present, UMD physics alumnus Jonathan Hoffman’s adviser gave him a signed copy of the book Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time. The book follows John Harrison, an 18th-century carpenter who took it upon himself to solve what was known as the longitude problem.

Jonathan Hoffman Jonathan Hoffman Back then, ships at sea had no way of measuring their longitude—their position east or west of the prime meridian—causing many to get lost and often shipwrecked as a result. Harrison built five generations of clocks—which he named H1 through H5—culminating in the most precise clock of his time that sailors could use to precisely track the sun’s location at noon and thus infer their longitude.

Longitude quickly became Hoffman’s favorite book. Eight years later, as a program manager at the Defense Advanced Research Projects Agency (DARPA), Hoffman started a new program called H6 seeking to build a ‘spiritual successor’ to Harrison’s clocks: a “6th clock” that would be a compact, affordable, and precise device that would help navigate in situations where a GPS signal is unavailable. “It's the clock that Harrison would build to solve today's timing problem,” Hoffman says. 

Harrison’s story was mired in controversy. In 1714, the British Parliament announced the Longitude Prize, an award of up to 20,000 pounds for anyone who could solve the longitude problem, but it was overseen by the royal astronomer—a proponent of the mainstream star-gazing (rather than Harrison’s timekeeping) approach. Although Harrison was awarded various prizes throughout his 45 years of work, he was never officially awarded the full prize.

As a program manager at DARPA, Hoffman’s role parallels not that of Harrison, but that of the Board of Longitude, which was established to oversee the prize. But his H6 program also seeks to avoid the mistakes made by that board. Instead of looking for a solution from a particular well-established technology, Hoffman wants to give scientists the opportunity to bring in new outside-the-box ideas. “I wanted to question if there’s a different way, a way of going back to the drawing board and making clocks, something that could be incredibly small but still maintain time correct to a microsecond for up to a week,” Hoffman says.

Scientific Roots

Hoffman hadn’t always had an eye toward project management. Like most who pursue a physics PhD, he grew up interested in science, broadly defined. “I always would like to grab books and look at astronomy pictures,” Hoffman recalls. Through high school and college, his interests in science, and physics in particular, deepened further. “I think it's fascinating that there's an underlying connection and description and law for how things function,” he says.

Entering graduate school at UMD in 2009, Hoffman intended to study string theory. “I was really enamored with the idea of understanding how all of the forces were unified,” he recalls. But a conversation with a theoretical physics professor at UMD steered Hoffman towards a more practical path in experimental physics. 

With an eye towards the future, Hoffman joined a lab overseen by Professors Luis Orozco and Steve Rolston, in collaboration with Fredrick Wellstood and Chris Lobb, working on a novel idea to combine different quantum computing technologies for the best of both worlds. The idea involved placing ultracold atoms—atoms cooled just a tad above absolute zero—next to superconducting qubits. Getting ultracold atoms and superconducting qubits close enough to each other and tuned appropriately to communicate with one another was a difficult proposition that had never been attempted before. To aid in the quest, the team decided to trap atoms in a light trap produced just outside an optical fiber. To coax an optical fiber into carrying most of the light just outside itself, rather than at its center, it was necessary to stretch the fiber incredibly thin—more than a hundred times smaller than a human hair.

The bulk of Hoffman’s graduate school work was to devise a technique for stretching optical fibers to that size, while ensuring that they continued to guide most of the light along their path. The requirements were stringent—just a few stray, unguided photons would destroy the superconducting state if they hit it. Virtually all of the light needed to remain guided by the fiber, trapping atoms. Hoffman and his labmates devised a bespoke machine for pulling the fiber, and a careful protocol that resulted in fibers that could retain a record 99.95% of the light.

Although the process was at times arduous, Hoffman credits his time in graduate school with teaching him to persist through a difficult problem. “Practically, day to day,” Hoffman says, “I don't think graduate school was as exciting and rewarding as what I do now. But it did teach some very important lessons about determination and focus.”

A Taste of the Bigger Picture

After graduating from UMD (and receiving his fortuitous graduation present) in 2014, Hoffman was still unsure what he wanted to do. A former student from the same lab told him about a job at Booz Allen Hamilton. “He said ‘you will help advise on who should get funding and you will follow people's work’,” Hoffman says. “And I didn't actually really understand what any of that meant, but I was lucky because I ended up loving it.”

The job description turned out to be exactly correct. At Booz Allen, Hoffman worked as an assistant to program managers at DARPA, learning about the work funded through the programs, and advising. “Having worked on a very particular problem for six years,” Hoffman says, “it was just an entirely broader array of subjects. I was looking at a field as a whole and seeing where there are technology gaps and how you can close them, helping advise on or what needs investment.”

Hoffman reveled in seeing the bigger picture and picking out areas where fundamental science, slightly refined, could benefit technology. He got to learn about and support programs in a broad array of fields, including atomic physics, chemical spectroscopy, integrated photonics and positioning, navigation, and timing. He worked alongside DARPA program managers and becoming one himself gradually became a career goal.

Inspired in part by Harrison’s story in the Longitude book, the related topics of positioning, navigation, and timing quickly became among Hoffman’s chief interests, along with quantum sensing. As the navigation-related program he was supporting was coming to a close, Hoffman realized that he wanted to dig deeper. As a Booz Allen Hamilton contractor, he would have been reassigned to other fields, so he found a new role at the Army Research Laboratory (ARL) where he was able to do a mix of research work and program management.

While at ARL, Hoffman collaborated with several UMD professors at the Quantum Technology Center and the Joint Quantum Institute. He worked closely with JQI Fellow and QTC Director Ronald Walsworth on quantum sensing problems—Walsworth’s area of expertise. He also continued thinking about positioning, navigation, and timing and started a program to create smaller clocks for portable GPS devices.

Juggling Programs and People

During his time at ARL, Hoffman was developing his ideas about alternative ways to make affordable yet precise clocks. When the opportunity arose to interview for a program management role at DARPA, he pitched his plan to encourage new approaches to the problem. “I guess they liked it well enough because they hired me,” Hoffman says.

Hoffman’s H6 program is set to begin in the coming months. Since arriving at DARPA in 2021, however, Hoffman’s interests have only broadened. He now dreams of a program to create portable MRI’s that could be an affordable tool in every doctor’s office and is managing other programs in quantum sensing and communication.

What he finds particularly rewarding about his work is the collaboration with a huge range of experts in different fields, from scientists to generals. “It is a really broad experience,” Hoffman says. “Working with academia, national labs, industry, large businesses, small businesses—it’s really great to get all of those perspectives and be able to interact with leaders across multiple fields.”

To continue interacting with many partners to make the best possible scientific advances, Hoffman encourages a broad range of people to work with DARPA and support their mission. He says people can come in as contractors, subject matter experts, apply for small business funding through various mechanisms, apply for young faculty awards, or apply for research grants and more.

Overall, Hofmann has no regrets about his transition from in-the-lab scientific work to program management. “It's absolutely important and it's fascinating and rewarding to understand and just be motivated by the specific science, but it's always been helpful for me having the larger picture of where this would go in the long-term plan.”

Story by Dina Genkina

Twisting Up Atoms Through Space and Time


Nearly 50-meter Laser Experiment Sets Record in Campus Hallway

It's not at every university that laser pulses powerful enough to burn paper and skin are sent blazing down a hallway. But that’s what happened in UMD’s Energy Research Facility, an unremarkable looking building on the northeast corner of campus. If you visit the utilitarian white and gray hall now, it seems like any other university hall—as long as you don’t peek behind a cork board and spot the metal plate covering a hole in the wall.A laser is sent down a UMD hallway in an experiment to corral light as it makes a 45-meters-long journey.A laser is sent down a UMD hallway in an experiment to corral light as it makes a 45-meters-long journey.

But for a handful of nights in 2021, UMD Physics Professor Howard Milchberg and his colleagues transformed the hallway into a laboratory: The shiny surfaces of the doors and a water fountain were covered to avoid potentially blinding reflections; connecting hallways were blocked off with signs, caution tape and special laser-absorbing black curtains; and scientific equipment and cables inhabited normally open walking space.

As members of the team went about their work, a snapping sound warned of the dangerously powerful path the laser blazed down the hall. Sometimes the beam’s journey ended at a white ceramic block, filling the air with louder pops and a metallic tang. Each night, a researcher sat alone at a computer in the adjacent lab with a walkie-talkie and performed requested adjustments to the laser.

Their efforts were to temporarily transfigure thin air into a fiber optic cable—or, more specifically, an air waveguide—that would guide light for tens of meters. Like one of the fiber optic internet cables that provide efficient highways for streams of optical data, an air waveguide prescribes a path for light. These air waveguides have many potential applications related to collecting or transmitting light, such as detecting light emitted by atmospheric pollution, long-range laser communication or even laser weaponry. With an air waveguide, there is no need to unspool solid cable and be concerned with the constraints of gravity; instead, the cable rapidly forms unsupported in the air. In a paper accepted for publication in the journal Physical Review XPhysical Review X the team described how they set a record by guiding light in 45-meter-long air waveguides and explained the physics behind their method.

The researchers conducted their record-setting atmospheric alchemy at night to avoid inconveniencing (or zapping) colleagues or unsuspecting students during the workday. They had to get their safety procedures approved before they could repurpose the hallway.

“It was a really unique experience,” says Andrew Goffin, a UMD electrical and computer engineering graduate student who worked on the project and is a lead author on the resulting journal article. “There's a lot of work that goes into shooting lasers outside the lab that you don't have to deal with when you're in the lab—like putting up curtains for eye safety. It was definitely tiring.”

 Left to right Eric Rosenthal, a physicist at the U.S. Naval Research Laboratory; Anthony Valenzuela, a physicist at the U.S. Army Research Lab; and Goffin align optics at a porthole in the wall in order to send the laser beam from the lab down the hallway. The white dotted lines show the approximate beam path before and after the optics redirected it. Left to right Eric Rosenthal, a physicist at the U.S. Naval Research Laboratory; Anthony Valenzuela, a physicist at the U.S. Army Research Lab; and Goffin align optics at a porthole in the wall in order to send the laser beam from the lab down the hallway. The white dotted lines show the approximate beam path before and after the optics redirected it. All the work was to see to what lengths they could push the technique. Previously Milchberg’s lab demonstrated that a similar method worked for distances of less than a meter. But the researchers hit a roadblock in extending their experiments to tens of meters: Their lab is too small and moving the laser is impractical. Thus, a hole in the wall and a hallway becoming lab space.

“There were major challenges: the huge scale-up to 50 meters forced us to reconsider the fundamental physics of air waveguide generation, plus wanting to send a high-power laser down a 50-meter-long public hallway naturally triggers major safety issues,” Milchberg says. “Fortunately, we got excellent cooperation from both the physics and from the Maryland environmental safety office!”

Without fiber optic cables or waveguides, a light beam—whether from a laser or a flashlight—will continuously expand as it travels. If allowed to spread unchecked, a beam’s intensity can drop to un-useful levels. Whether you are trying to recreate a science fiction laser blaster or to detect pollutant levels in the atmosphere by pumping them full of energy with a laser and capturing the released light, it pays to ensure efficient, concentrated delivery of the light.

Milchberg’s potential solution to this challenge of keeping light confined is additional light—in the form of ultra-short laser pulses. This project built on previous work from 2014 in which his lab demonstrated that they could use such laser pulses to sculpt waveguides in the air.

The short pulse technique utilizes the ability of a laser to provide such a high intensity along a path, called a filament, that it creates a plasma—a phase of matter where electrons have been torn free from their atoms. This energetic path heats the air, so it expands and leaves a path of low-density air in the laser’s wake. This process resembles a tiny version of lighting and thunder where the lightning bolt’s energy turns the air into a plasma that explosively expands the air, creating the thunderclap; the popping sounds the researchers heard along the beam path were the tiny cousins of thunder.

But these low-density filament paths on their own weren’t what the team needed to guide a laser. The researchers wanted a high-density core (the same as internet fiber optic cables). So, they created an arrangement of multiple low-density tunnels that naturally diffuse and merge into a moat surrounding a denser core of unperturbed air.

The 2014 experiments used a set arrangement of just four laser filaments, but the new experiment took advantage of a novel laser setup that automatically scales up the number of filaments depending on the laser energy; the filaments naturally distribute themselves around a ring.

The researchers showed that the technique could extend the length of the air waveguide, increasing the power they could deliver to a target at the end of the hallway. At the conclusion of the laser’s journey, the waveguide had kept about 20% of the light that otherwise would have been lost from their target area. The distance was about 60 times farther than their record from previous experiments. The team’s calculations suggest that they are not yet near the theoretical limit of the technique, and they say that much higher guiding efficiencies should be easily achievable with the method in the future.

“If we had a longer hallway, our results show that we could have adjusted the laser for a longer waveguide,” says Andrew Tartaro, a UMD physics graduate student who worked on the project and is an author on the paper. “But we got our guide right for the hallway we have.”Distributions of the laser light collected after the hallway journey without a waveguide (left) and with a waveguide (right). Distributions of the laser light collected after the hallway journey without a waveguide (left) and with a waveguide (right).

The researchers also did shorter eight-meter tests in the lab where they investigated the physics playing out in the process in more detail. For the shorter test they managed to deliver about 60% of the potentially lost light to their target.

The popping sound of the plasma formation was put to practical use in their tests. Besides being an indication of where the beam was, it also provided the researchers with data. They used a line of 64 microphones to measure the length of the waveguide and how strong the waveguide was along its length (more energy going into making the waveguide translates to a louder pop).

The team found that the waveguide lasted for just hundredths of a second before dissipating back into thin air. But that’s eons for the laser bursts the researchers were sending through it: Light can traverse more than 3,000 km in that time.

Based on what the researchers learned from their experiments and simulations, the team is planning experiments to further improve the length and efficiency of their air waveguides. They also plan to guide different colors of light and to investigate if a faster filament pulse repetition rate can produce a waveguide to channel a continuous high-power beam.

“Reaching the 50-meter scale for air waveguides literally blazes the path for even longer waveguides and many applications”, Milchberg says. “Based on new lasers we are soon to get, we have the recipe to extend our guides to one kilometer and beyond.”

Story by Bailey Bedford. Images by Intense Laser-Matter Interactions Lab, UMD.

In addition to Milchberg, Goffin and Tartaro, Aaron Schweinsburg and Anthony Valenzuela from the DEVCOM Army Research Lab, and Eric Rosenthal from the Naval Research Lab are also authors and Ilia Larkin, a former UMD graduate student and current systems engineer at KLA, is a co-lead author.

Publication information:

PI affiliations: Howard Milchberg is jointly appointed to the departments of Physics and Electrical and Computer Engineering and is affiliated with the Institute for Research in Electronics and Applied Physics.

This work is supported by the Office of Naval Research (N00014-17-1-2705 and N00014-20-1-2233), the Air Force Office of Scientific Research and the JTO (FA9550-16-1-0121, FA9550-16-1-0284, and FA9550-21-1-0405), the  Army Research Lab (W911NF1620233) and the Army Research Office (W911NF-14-1-0372).