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BYLINE: Leah Hesla
Newswise — With enough information, humans can make solid, bang-on predictions — about the rise time of a bread loaf, the lifetime of a diseased cell, the exact time of a solar eclipse. That’s the triumph of science. The triumph of nature is that we can still be surprised.
As a middle schooler taking his first physics class, Benjamin Pingault was drawn to that cycle of surprise and prediction.
“You could predict the future,” he said. “You know your system. You describe it. You use a few formulas, and you can predict what will happen. And it works. I thought, ‘That’s the closest thing we have to magic.’”
That predictive power becomes even more remarkable when you consider that researchers use it to model and control the enigmatic behavior of atoms — the foundation of quantum physics. Pingault, a scientist at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, develops qubits, engineering these packets of quantum information for future technologies such as hackerproof telecommunication and ultraprecise sensors.
“People don’t realize how good they are at physics … You know how [a] ball [thrown into the air] will move. You’re processing physics in your head. Quantum is just changing the rules a bit.” —Benjamin Pingault, Argonne scientist
Creating color centers
A co-investigator within Q-NEXT, a DOE National Quantum Information Science Research Center led by Argonne, Pingault focuses on a type of qubit called a color center. A color center is created when an atom is missing or replaced by another type of atom in a crystal. For example, one can remove two adjacent carbon atoms from diamond and swap one out with a tin atom. Presto chango — you have a tin vacancy, one of many color center types. (The term “color center” comes from the fact that the irregularity gives the crystal a specific hue.)
The quantum information community has been drawn to color centers because they serve as an interface between light and something called “spin.” A tiny quantum magnet pinned to the color center, the spin serves as its information-processing core. Like an atom-scale memory chip, the color center stores spin-encoded information, transmitting it as particles of light (photons) or even tiny vibrations (phonons).
Working at the Argonne Quantum Foundry, Pingault studies what makes good color centers and puts them through their paces. How is the qubit affected by its environment? How do you engineer it to transmit useful photons? Or phonons?
“The work is very creative, in a sense,” said Pingault, who got into quantum information following an internship that introduced him to qubit engineering. “There was the aspect of controlling something at an atomic scale that I found fascinating. You can remove your sample, put it back, and it behaves the same. And you’re dealing with only one or two atoms. Again, it was almost magic.”
Fine-tuning signals
Although you’re dealing with only one or two atoms, the way you talk to color centers is very much at the human-scale: Conversations with color centers entail lasers, lots of mirrors, photon detectors and microwave sources, similar to what’s used in your microwave oven.
“I like the fact that with these color centers, you get to really tweak the experiment yourself. It’s not a black box where you put the sample in and wait for results,” Pingault said. “You get to align the mirrors and lasers, choose the optics you put on the table, design the microwave circuitry you want to use. You can add an extra filter, and it is pretty quick. You’re fine-tuning your system quite easily.”
The color center’s easy accessibility has a flip side. Because the qubit is not isolated but instead surrounded by hundreds of billions of atoms that influence the spin, it sits in a noisy environment that the spin-encoded signal must penetrate.
“It’s a little bit like you’re trying to have a conversation with a friend who’s in the middle of Times Square, and you need to hear your friend perfectly,” Pingault said. “And you’re at the Statue of Liberty or even in San Francisco.”
To tamp down the noise, scientists often cool their qubits to near absolute zero in special refrigerators, creating a quiet environment for sending and receiving quantum information.
Pingault focuses on color centers made from group IV elements of the periodic table, such as silicon, germanium and tin. They have the advantage of emitting very precise colors of photons determined by the state of their spins, making them useful for transmitting information over metropolitan-scale quantum networks. And since these qubits are sensitive to vibrations, scientists can also drive the spin by giving it an atom-scale tap, generating phonons, which are useful for transmitting information over chip-scale distances. Through Q-NEXT, Pingault works to scale up quantum technologies based on these group IV color centers in diamond.
Many-splendored science
While group IV color centers are Pingault’s qubit of choice, there’s no best qubit, he says.
“I think the ideal material doesn’t really exist,” Pingault said. “It’s about getting the best material combined with the best practices and best protocols. That’s why you need to tailor all three at the same time. You need to understand what’s happening from a physics point of view to tailor your system to a given application.”
In other words, play to the material’s strengths. For every use, there’s a technology. It’s a broad-minded take, one that Pingault maintains beyond materials science. Having conducted research in six countries on three continents, Pingault has a prismatic perspective on approaches to problem-solving and collaboration.
“Research can be quite culturally dependent,” he said. “Experiencing different ways and approaches of doing research helped me refine what works best for me.”
Scientific culture is hierarchical at some organizations. At others, independence is encouraged. Similarly, the ways we learn science are shaped by individual needs: Some students prefer to teach themselves. Others appreciate more guidance.
“Tailoring the research environment to the person that you’re supervising and mentoring helps them, and it helps you collaborate in the most fruitful way,” he said.
Pingault received his undergraduate degree from Paris-Saclay University and ESPCI in France. The education journey that followed took him to Germany, Japan, the United Kingdom, the United States and the Netherlands. He completed his doctoral degree at the University of Cambridge, and after two subsequent fellowships, joined Argonne and the University of Chicago as a staff scientist in 2023.
As one might expect, Pingault’s picked up a few languages along the way. He’s fluent or conversant in three and a student of at least eight others.
“Knowing languages helps you understand how people think — just based on the structure of the language, the vocabulary that’s used, what the language highlights,” said Pingault, who compares language to how physics works. “You’ve got a set of rules that you can be creative with. You might uncover different ways of doing the same things or optimize for certain purposes.”
And in both cases, with enough practice, you build an intuition for how things work — a fact too many doubt when it comes to quantum science. Its reputation as a domain reserved for geniuses is misplaced, Pingault says. It’s like any discipline: With effort, familiarity becomes fluency.
“People don’t realize how good they are at physics,” he said. Just as we can predict the arc of a ball thrown into the air, with training, we can develop an intuition for quantum physics. “You know how the ball will move. You’re processing physics in your head. Quantum is just changing the rules a bit.”
That we can intuit the behavior of an atom, shape the forces that govern a thing so small, and harness them for information-sharing are the thrills of quantum science. And because nature’s complexity is infinite, the thrills will keep coming.
“Nothing is actually mundane. Nothing is usual. Even a simple chair, the material it’s made of, its structure — everything has been adapted to a certain purpose,” Pingault said. “There’s always some underlying complexity to anything that looks simple and obvious.”
And discovery typically begins where certainty ends.
“We never know enough, but I think that’s helpful. Approaching things in different ways and seeing things from different perspectives helps you remain curious,” Pingault said. “If you’re not feeling a bit stretched, you’re probably not discovering anything. It’s important to challenge what we know.”
This work was supported by DOE’s Office of Science National Quantum Information Science Research Centers as part of the Q-NEXT center.
About Q-NEXT
Q-NEXT is a U.S. Department of Energy National Quantum Information Science Research Center led by Argonne National Laboratory. Q-NEXT brings together world-class researchers from national laboratories, universities and U.S. technology companies with the goal of developing the science and technology to control and distribute quantum information. Q-NEXT collaborators and institutions have established two national foundries for quantum materials and devices, develop networks of sensors and secure communications systems, establish simulation and network test beds, and train the next-generation quantum-ready workforce to ensure continued U.S. scientific and economic leadership in this rapidly advancing field. For more information, visit https://q-next.org/.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology by conducting leading-edge basic and applied research in virtually every scientific discipline. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.
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