Researchers led by Prof. Giulia Galli at the University of Chicago’s Pritzker School of Molecular Engineering report a computational study that predicts the conditions to create specific spin defects in silicon carbide. Their findings, published online in Nature Communications, represent an important step towards identifying fabrication parameters for spin defects useful for quantum technologies.
Electronic spin defects in semiconductors and insulators are rich platforms for quantum information, sensing, and communication applications. Defects are impurities and/or misplaced atoms in a solid, and the electrons associated with these atomic defects carry a spin. This quantum mechanical property can be used to provide a controllable qubit, the basic unit of operation in quantum technologies.
Yet the synthesis of these spin defects, typically achieved experimentally by implantation and annealing processes, is not yet well understood and, importantly, cannot yet be fully optimized. In silicon carbide — an attractive host material for spin qubits due to its industrial availability — different experiments have so far yielded different recommendations and outcomes for creating the desired spin defects.
“There hasn’t yet been a clear strategy to engineer the formation of spin defects to the exact specifications we want, a capability that would be highly advantageous for advancing quantum technologies,” says Galli, the Liew Family Professor of Molecular Engineering and Chemistry, who is the corresponding author of the new paper. “So, we embarked on a long computational journey to ask the following question: Can we understand how these defects form by carrying out comprehensive atomistic simulations?”
Galli’s team—including Cunzhi Zhang, a postdoctoral researcher in Galli’s group, and Francois Gygi, a professor of computer science at the University of California, Davis—have combined multiple computational techniques and algorithms to predict the formation of specific spin defects in silicon carbide known as “divacancies”.
“Divacancies are created by removing a silicon and a carbon atom sitting close together in a silicon carbide solid. We know from previous experiments that these types of defects are promising platforms for sensing applications,” Zhang says.
Quantum sensing could enable detection of magnetic and electric fields and also reveal how complex chemical reactions occur, beyond what’s possible with today’s technologies. “To unlock quantum sensing capabilities in the solid-state, we first need to be able to create the right spin defects or qubits at the right location.” Galli says.
To find a recipe for predicting the formation of particular spin defects, Galli and her team combined several techniques to help them look at the movements of atoms and charges when a defect forms as a function of temperature.
“Typically, when a spin defect is created, other defects also appear and those may negatively interfere with the targeted sensing capabilities of the spin defect,” says Gygi, the main developer of the first-principles molecular dynamics code Qbox used in the team’s quantum simulations. “Being able to fully understand the complex mechanism of defect formation is very important.”