Diamond is extremely valuable to science and technology not for its sparkle but for its extreme hardness, high thermal conductivity, transparency to a large fraction of the light spectrum, and a host of other exceptional properties. Two decades ago, scientists discovered another advantage: under the right conditions, diamond can become a superconductor—allowing electricity to flow through it with zero resistance.
Until recently, though, they knew little about how that happens, limiting its use in high-tech applications.
Now researchers from the Pennsylvania State University, the University of Chicago Pritzker School of Molecular Engineering (PME), and the U.S. Department of Energy National Quantum Information Science Research Center Q-NEXT, led by Argonne National Laboratory, have uncovered new insights into the physics behind the phenomenon by carefully creating high-quality diamond, isolating electronic signatures from material noise, and revealing the fundamental mechanisms that had long remained hidden.
The study, recently published in Proceedings of the National Academy of Sciences, offers a potential roadmap for enabling multiple functions on one quantum chip — an innovation that could make quantum technologies more efficient and better able to integrate with classical technologies. The key is in the capabilities of different kinds of qubits, or quantum bits, the building blocks of quantum technologies. Right now, it can be difficult to connect quantum technologies with disparate qubits, but enabling them both in a single material, particularly a thermally efficient semiconductor as versatile as diamond, could have powerful implications.
“This offers a new way of thinking by integrating superconducting and semiconductor behavior to create opportunities for multifunction quantum devices,” said David Awschalom, the Liew Family Professor of Quantum Science and Engineering and Physics at UChicago PME and the director of the Chicago Quantum Exchange. “Imagine a future technology that combines light, spin, superconductivity, and magnetism, all in a single material that one could also integrate with today’s microelectronics. There’s enormous potential at the interface between these nominally disparate areas of science that may be developed through a deeper physical understanding of the system through precise atomic-scale engineering.”
How it works
In order to become superconducting, diamond must be “doped” with atoms of boron. (Doping is the process of adding different atoms to a host material to control or change certain properties, such as electrical conductivity).
In the study, the scientists used a facility at Penn State’s Applied Research Lab to synthesize extremely high-quality diamond thin films doped with a random distribution of boron. Surprisingly, the research team found hidden order within this disordered distribution of boron in the form of a mosaic of superconducting “puddles” that must eventually link up to allow electricity to flow without resistance – which they describe as “granular superconductivity”. These puddles might form due to clustering of boron atoms within diamond, however even in microscopically uniform films, the superconductivity was found to be granular. More importantly, the superconducting mosaic is seemingly tunable and can be stretched and skewed by changing the magnetic field, electrical current and temperature.
“The graduate student leading the project discovered complex patterns in the electrical behavior of the films that could only be explained by intrinsic granularity,” said Nitin Samarth, Verne M. Willaman Professor of Physics and Materials Science and Engineering at Penn State and co-corresponding author of the paper. “This serendipitous discovery caught us totally by surprise because these are structurally homogeneous, crystalline films! So, the question was: where is this granularity coming from?”
By identifying how electrons move through and between these superconducting puddles, scientists can now begin to "stitch" these superconducting puddles together more effectively, which could significantly boost the performance and temperature range of future quantum devices. Currently, these systems require extreme cooling to function; raising that temperature would make quantum technology more accessible and energy-efficient.
Potential for new innovations
One of the most exciting implications of this research, says Awschalom, is the potential for multifunctional ‘quantum-on-chip’ applications, where multiple different types of quantum information technologies—like quantum communication and quantum computing—could coexist and work together on a single diamond chip. This is due to diamond’s built-in “spin-photon interface,” meaning it naturally connects light to matter without any other technology necessary.
As the quantum industry looks to develop a domestic diamond supply chain, this “all-in-one” diamond platform offers a path toward chips that are not only more powerful but also easier to integrate with the classical high-frequency electronics we use today.
These applications are only possibilities, but the study has taken a critical step: by understanding the underlying principles behind superconductivity in diamond, researchers can now move beyond simply observing it to actively engineering it.
“We now have a reliable roadmap for engineering diamond superconductors by independently adjusting the material’s core properties,” says Samarth, “By tuning parameters like boron doping density, crystalline orientation, mechanical strain, and dimensionality, we can move beyond simple observation and start designing diamond superconductors for specific roles. There are a lot of exciting possibilities here, for both quantum and classical technology.”