Researchers at the University of Chicago Pritzker School of Molecular Engineering have created a computational framework to fully model the energy loss from spin defects, a historically difficult process to predict. These defects, embedded in materials like diamond and silicon carbide, are being investigated as stable qubits for quantum sensing technologies.
The new approach accurately predicts internal conversion, where energy dissipates as atomic vibrations instead of light, by accounting for complex interactions within realistic solid models. “This internal conversion process is not only relevant to spin defects—it’s also related to processes of interest to energy technologies,” said Giulia Galli, the Liew Family Professor of Electronic Structure and Simulations.
UChicago PME Framework Models Internal Conversion in Spin Defects
This capability stems from a full optical cycle simulation of these defects, offering a significant advancement in understanding their behavior for quantum technologies and beyond. Implementation of the framework relies on the WEST code, an open-source simulation program developed by Galli’s group since 2015 with funding from the U.S. Office of Basic Energy Sciences, through the Midwest Integrated Center for Computational Materials (MICCoM).
The team’s success hinged on addressing the computational challenges inherent in accurately describing these complex interactions. The framework’s ability to model internal conversion, alongside other relaxation pathways like photon emission and spin transitions, provides a complete picture of how these defects respond to excitation.
The significance of accurately modeling internal conversion extends beyond quantum sensing applications, with potential implications for renewable energy technologies. Stefano Villani, a PME postdoctoral researcher and the study’s first author, explained that “Although the equations are known, it’s hard to describe the process accurately because of computational difficulties.” He added that accounting for complex interactions between the electrons and surrounding atoms is challenging in realistic solids represented by models with hundreds or thousands of atoms.
This internal conversion process is not only relevant to spin defects-it’s also related to processes of interest to energy technologies.
Giulia Galli, the Liew Family Professor of Electronic Structure and Simulations in UChicago PME and the Department of Chemistry and the senior author of the study
WEST Code Predicts Energy Loss in Silicon Carbide Divacancies
Calculations using the WEST code revealed a previously underestimated energy loss pathway in silicon carbide divacancies, challenging existing assumptions about their behavior as potential qubits. The team’s simulations demonstrated that internal conversion, a non-radiative decay process, contributes significantly to the excited-state lifetime of these defects, resolving a discrepancy between theoretical predictions and experimental observations.
“We were expecting to see an effect, but of a smaller magnitude,” said Giulia Galli, noting the unexpected importance of this phenomenon. The framework’s success hinged on a complete mathematical derivation of the process, something previously lacking despite known equations, and efficient algorithms for its implementation.
While the framework accurately predicted energy loss in nitrogen-vacancy centers in diamond, confirming established understanding of singlet and triplet state behavior, the silicon carbide results were particularly revealing. The team is now focused on reducing the computational demands of the framework, exploring integration with machine learning to accelerate excited-state calculations and broaden its applicability to other materials relevant to both quantum technologies and renewable energy conversion.
This internal conversion process is not only relevant to spin defects-it’s also related to processes of interest to energy technologies.
Giulia Galli, the Liew Family Professor of Electronic Structure and Simulations in UChicago PME and the Department of Chemistry and the senior author of the study
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