Materials Science, Chemistry Key to QIS—and NU Excels There, Too

Quantum research at Northwestern is truly a team effort at all levels.”

Mark Hersam

The field of quantum information science (QIS) relies heavily on physics—and many think about it in those terms—but materials science and chemistry are also critical to the success of quantum technologies like computing, sensing and communications, according to Mark Hersam, PhD, chair of the materials science and engineering department and director of the materials research center at Northwestern’s McCormick School of Engineering.

“Ultimately, if you want to realize a practical technology, you are going to need a materials platform on which to have your quantum devices operating,” he says. “And chemistry is essential to materials. The surfaces of materials are typically chemically reactive and need to be controlled and passivated. And so, absolutely, materials and chemistry are critical.”

In quantum computing, for example, the most popular and commercially developed technologies are based on superconducting qubits—used by companies like IBM, Google and Rigetti Computing—which have a parameter known as coherence time, referring to how long they can hold the quantum state, says Hersam, also the Walter R. Murphy Professor of Materials Science and Engineering, and a professor of electrical and computer engineering and chemistry.

That coherence time “is limited by materials defects in the superconductor and the surrounding materials in the hardware,” he says. “Efforts in our lab and in others at Northwestern are focused on understanding those atomic-level origins of decoherence and then developing mitigation strategies. The chemistry of those materials is critical to that goal.”

Regarding quantum communication, the mode of communication typically uses light, or photons—and generating single photons is important to the success of a given application, Hersam says. “Certain materials, including materials in my lab, have shown promise for generating high-purity single photons,” he says.

In quantum sensing, Hersam and his colleagues are working to develop molecular qubits, molecules that serve as the qubit and can be directly deposited on top of whatever one is trying to detect. “Another advantage of molecular qubits is that when you synthesize them, you can make very large numbers of identical qubits, and then you can tailor their properties by changing the ligands on those molecules,” he says. “Chemistry is critical to making molecules, of course.”

Qubits provide a very high sensitivity to magnetic and electric fields, and one challenge researchers at Northwestern and elsewhere have faced is how to deposit those sensors as close as possible to what they’re trying to detect, Hersam says. One of the most popular platforms for quantum sensing is based on defects in diamonds that only show high sensitivity when they are located below the surface of the material.

“In contrast, molecules can be deposited directly on top of the surface, allowing closer proximity to the specimen being detected,” he says. “Or if you want to detect something that binds to the top surface, it is in direct contact with the sensor. Again, this is a case where chemistry is critical, particularly molecular qubits are critical, to getting high performance. Nearly anything that you want to detect becomes possible by tailoring the surface chemistry to specifically bind to the target.”

Developing Quantum Curricula

The highly interdisciplinary nature of quantum is a key consideration in developing curricula for the field, which still needs refining given how new the field is, Hersam says. “You need to have expertise in physics, for sure, and additionally, materials science and chemistry,” he says. “If you are working on quantum sensing, particularly biosensing, you also will need to know some biology. And to make technologies work, you need to think like an engineer. Ultimately, highly interdisciplinary training is essential for quantum technologies.”

The type(s) of engineering that will be relevant depend on what aspect of quantum you’re working on, Hersam says. For example, quantum computing requires knowledge of electrical engineering on the hardware side and computer science on the software side. “Quantum information science presents a challenge and an opportunity for educators to develop curricula that span those topics, which are quite broad,” he says. “In addition to breadth, quantum curricula will need to have specializations so that students who graduate from such programs do not just have cursory knowledge of lots of things, but also have rigor in at least one of those areas.”

Northwestern offers expertise in all of those areas, as the second-ranked materials science program in the country—and the site of the first-ever materials science department—and the sixth-ranked chemistry program, according to U.S. News & World Report. Hersam also mentions colleagues at the top of their respective fields, including Jens Koch, PhD, professor of physics and astronomy; and Michael Wasielewski, PhD, Clare Hamilton Hall Professor of Chemistry.

“We have exceptional strength in materials, broadly, and that includes quantum materials,” Hersam says. “Chemistry is also critical to the leadership of the quantum effort, as is physics. … For example, Jens Koch in our physics department is a pioneer of the transmon qubit, which underlies most of the commercially available quantum computers. Northwestern also has great strength in electrical engineering and computer science, which are of critical interest to quantum computing.”

Tying that together, he adds, is the fact that “Northwestern is one of the most interdisciplinary universities in the world. That interdisciplinary tradition has been developed over the past several decades at Northwestern and is especially important for quantum technologies.”

‘A Team Effort’

That explains why funding for QIS research projects at Northwestern is invariably shared by multiple principal investigators (PIs), Hersam says. “Quantum research at Northwestern is truly a team effort at all levels,” he says. “Certainly at the faculty level, but also going down to post-docs, graduate students and undergraduate students. That is the secret sauce at Northwestern: the fact that we have that interdisciplinary mix, and a long tradition of working together. It is no surprise that all of my quantum efforts are funded through multi-PI mechanisms.”

Quantum computing efforts at Northwestern are part of the Superconducting Quantum Materials and Systems (SQMS) Center, a National Quantum Initiative center led by Fermilab, with NU as the academic center, and including many other institutions such as Rigetti Computing, Hersam says.

“The SQMS Center is a case where we are bridging between the fundamental science of decoherence and the engineering of quantum devices,” he says. “Importantly, some of the methods that we are developing to mitigate decoherence have been pursued in close collaboration with Rigetti Computing, thereby providing a direct path to commercializing those developments.”

In the end, an important quality of quantum innovation is that it not only involves university research but also technology translation to industry, Hersam says. “Ultimately, we impact society not only through the students that we graduate, but also through the technologies that make it into the hands of consumers,” he says.