Making the atomic universe visible

As a teenager in Mauritius, an island nation off the East African coast, Nitin Samarth sank himself in the study of the stars. A member of his school’s astronomy club, he regularly recorded astronomical data, sending it abroad to professional astronomy societies. He and his 14-year-old club cohorts even petitioned their school to let them voyage into the Indian Ocean to experience totality during an upcoming solar eclipse.

“Naturally, this request was totally turned down,” said Samarth, the Verne M. Willaman professor of physics and of materials science and engineering at Penn State.

“When astronomers map out the sky, they make that data available to the community. … So in that same sense, we want to make the materials universe visible to the community so that anyone can go in and explore the data.”  — Nitin Samarth, Penn State

The curiosity that drove Samarth to explore the sky now drives him to plumb the atomic realm.

As a researcher at Penn State, Samarth develops atomic states of matter for quantum technologies, catalogs their features and makes the data available to all — continuing the tradition of community science for which astronomy is famous.

“When astronomers map out the sky, they make that data available to the community,” Samarth said. ​“So in that same sense, we want to make the materials universe visible to the community so that anyone can go in and explore the data.”

It’s an important but unsung contribution to quantum technologies, which are expected to revolutionize areas such as finance and medicine in the coming decades. Headlines tout the potentially game-changing impact of quantum computers, but less media attention is paid to the atomic materials that lie at their foundation.

Scientists manipulate atomic states of matter in countless ways to create qubits — the fundamental units of quantum information. What features make these materials viable quantum-information carriers? How do you engineer them to bring out those features? Which properties are best suited to which uses?

A collaborator within Q-NEXT — a U.S. Department of Energy (DOE) National Quantum Information Science Research Center led by DOE’s Argonne National Laboratory — Samarth is a leader both in growing quantum materials and in building open libraries of quantum-materials data.

A materials world

For Samarth, the universe of quantum materials is an expansive atom-scale playground full of twists and turns.

“There are so many parameters that come into play in determining the properties of a material. And it’s because of this combination of so many parameters that we can get interesting surprises,” Samarth said. ​“It is not so easy in a predictable way to achieve a result. And that’s what keeps me excited.”

As part of Q-NEXT, Samarth is helping grow the capabilities of the Argonne Quantum Foundry, whose recent establishment was one of Q-NEXT’s achievements. An expert in creating different types of crystals for hosting qubits, Samarth advises other foundry researchers on promising avenues of exploration, advancing state-of-the-art quantum materials for real-world applications.

“When Q-NEXT came along, I got interested in the idea that, with this quantum foundry, maybe I can develop some materials that others in the foundry may not have the bandwidth to develop,” he said.

One material in particular has been of special interest to him and his Penn State group: boron-doped diamond.

Diamond is a popular material for hosting qubits: It’s good at sustaining the qubit’s lifetime, and it’s easily incorporated into today’s information technologies.

The qubit itself takes the form of a nitrogen vacancy (NV) center: One of diamond’s carbon atoms is replaced by a nitrogen atom and an atom-sized hole. Using a laser, a scientist controls the NV center’s ​“spin” — a property of all atomic matter — to process quantum information. When boron is incorporated into the diamond in just the right way, scientists can systematically engineer the NV center’s behavior as a qubit.

Boron’s capabilities don’t stop there. Astonishingly, at high densities, boron can convert diamond from a nonconducting to a superconducting material.

Samarth and the Q-NEXT team are excited about the prospects of boron-doped diamond for quantum technologies: Two foundational platforms for quantum information processing — superconducting devices and NV centers — could be integrated within a single material.

To realize the material’s potential, Samarth is pioneering the challenging process of controlling the placement of boron in thin films of diamond, mere micrometers thick, less than a tenth of the width of a human hair.

“We’re opening up a niche aspect of the foundry dedicated to the synthesis of this material,” he said.

Even as he spearheads this specialty line of research, he continues to share his work with the community by building materials databases that anyone can access. As the associate director of the 2D Crystal Consortium (2DCC) at Penn State, Samarth has been part of the team developing the consortium’s Lifetime Sample Tracking System, which has cataloged the properties of hundreds of atom-scale materials.

“You can look up any of the hundreds of samples that have been grown and all the parameters that have been varied,” he said.

The science of sharing science is its own pursuit.

“The challenge has been understanding what we need to capture from a particular synthesis process and the easiest way to get all this information into a database,” Samarth said. ​“You want some way in which everything that we’re entering into the electronic lab notebook is easily sucked in by this database system without imposing extra burdens on the scientists running the synthesis tools. My colleagues in the 2DCC have done a superb job in developing such a framework!”

Q-NEXT will use some of the system’s database tools to track the structural properties, growth conditions and other technical aspects of materials synthesized at the Argonne Quantum Foundry.

“So there’s now a nice collaboration between the foundry and colleagues within the 2DCC at Penn State,” Samarth said. ​“The software that we’ve developed can be of use broadly to the community.”

It’s difficult to pin Samarth’s exploration of the atomic universe to one type of material. When he isn’t researching diamond, he’s investigating the spin properties of materials whose behavior can be described using concepts from the field of topology. Topology is a branch of mathematics focused on space and how it changes when transformed by bending or stretching, for example. These seemingly exotic mathematical concepts can be applied to quantum-physical behaviors.

“We can use these concepts to build energy-efficient quantum memory architectures under real-life conditions,” Samarth said.

And in a recent collaboration led by his Penn State colleague Cui-Zu Chang, scientists used the 2DCC facility to create superconducting material from two nonsuperconducting magnetic compounds. As an added bonus, these compounds can also be manipulated according to topological principles.

Together, Samarth’s work advances materials needed to build a viable quantum computer.

“Who knows whether these materials will ever be important for quantum technology or not. There’s a lot more that has to be done before you can make them useful,” he said. ​“But it’s a good start. It’s always nice to have surprises.”

The accidents of exploration

And as Samarth will tell you, curiosity begets useful surprises.

When he was starting out as an assistant professor at Penn State, Samarth got curious about what could happen when you manipulated spins in semiconductors. Semiconductors were already popular — they’re the foundation of computer chips. But spin-dependent phenomena in semiconductors were new research territory. What cool things could one do?

“My main interest was: Can I go and look at phenomena that are not yet at the stage of being useful for technology?” Samarth said. ​“There were fundamental questions to be answered. If you could answer those questions, then you could envision a path toward a useful technology.”

The questions were straightforward: How long can the spin maintain quantum information? A nanosecond? A femtosecond? How long does the spin propagate? Samarth and a small science community began designing materials they could probe for answers.

“It was great fun. It was the stage of the field where we could ask very simple questions and get very direct answers,” Samarth said. ​“Somehow, by going after interesting questions of that kind, we were able to show that spins in semiconductors could retain their lifetimes at room temperature for long enough to be useful.”

It was an unexpected result born from pure exploration.

Surprises continued to spring from studying semiconductor spin. Early in Samarth’s career at Penn State, in a collaboration with a colleague at the University of California, Santa Barbara (now director of Q-NEXT, David Awschalom of the University of Chicago), the graduate students made a discovery about one of Samarth’s semiconductor samples — ​“one of the most boring samples we could make, honestly,” Samarth observed wryly: This most ordinary sample exhibited spin lifetimes in the nanosecond range — a healthy timespan in the quantum world.

“And that was not the aim of the project at all,” Samarth said. ​“The data was beautiful. It gives me a thrill to look at it, because it was a serendipitous discovery. That’s what really then got us to think seriously about spins in semiconductors and using them as qubits.”

The small semiconductor-spin-studying community of the 2000s has since grown to a substantial branch of quantum research, which itself arose from asking the question, ​“What practical uses can we make of nature’s quantum properties?”

“I’ve always been fascinated by quantum mechanics because it’s one of those aspects of our current understanding of the universe that never ceases to surprise me,” Samarth said. ​“I can honestly say that I don’t understand quantum mechanics, because at a purely intuitive level, it challenges your understanding at every stage of trying to approach a quantum mechanical problem. And yet we know it works.”

And with each surprise, quantum technology tends toward the useful, the practical, the beneficial.

“The idea that one can use quantum technologies to really open up new ways to interrogate, to probe our universe, is fascinating,” Samarth said. ​“It’s going to be a while before society broadly benefits from quantum technologies, but the pace at which we are going over the last 10 years has completely amazed me.”

This work was supported by the DOE 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://​ener​gy​.gov/​s​c​ience.