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: https://journals.aps.org/prx/accepted/8707dK4dIb91a60bb6df4e56bdc44a53b2267be80

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).

Jonathan D. Moreno Named Third Milchberg Lecturer

Jonathan D. Moreno,  the David and Lyn Silfen University Professor at the University of Pennsylvania, gave the third Irving and Renee Milchberg Endowed Lecture on Tuesday, April 4, 2023.

Moreno's talk addressed Bioethics and the Rules-Based International Order.   Jonathan Moreno. Credit: University of PennsylvaniaJonathan Moreno. Credit: University of Pennsylvania

Moreno, an elected member of the National Academy of Medicine, studies medical ethics and health policy, the history and sociology of science, and philosophy. He received  his Ph.D. in philosophy from Washington University in St. Louis and was an Andrew W. Mellon post-doctoral fellow. His book The Body Politic: The Battle Over Science in America was a Kirkus Reviews Best Book of the Year and a Scientific American Book Club selection. More recently, he wrote Everybody Wants to Go to Heaven but Nobody Wants to Die: Bioethics and the Transformation of Healthcare in America with former Penn President Amy Gutmann.

Moreno received the 2018 Lifetime Achievement Award of the American Society for Bioethics and Humanities. 

The Irving and Renee Milchberg Endowed Lectureship was established by Prof. Howard Milchberg and his wife Rena, to remember Howard's parents, who survived the Holocaust and the distortions of truth that accompanied and facilitated it.  Milchberg’s mother and father, who died in 2017 and 2014, respectively, never received formal education, but Milchberg describes them as “remarkably open-minded and tolerant” and as “wide-ranging thinkers and skeptics.”