Researchers have developed a new computer modeling method that allows for more accurate prediction and tuning of key magnetic properties in molecular qubits, a significant component in quantum technology. This advancement is expected to help design longer-lasting and more reliable qubits, which are crucial for the development of future quantum computers and detectors.
The team, led by University of Chicago Professor Giulia Galli, focused on chromium-based molecular qubits. Their computational approach enables scientists to predict how these qubits will behave based on their material environment, particularly by examining features such as zero-field splitting (ZFS), which determines the energy levels used to encode quantum information.
“I think this work will open new venues for the simulations of molecular qubits from first principles, and I see it as a real starting point for many new investigations to come, especially on the assembly of molecular qubits,” said Prof. Giulia Galli.
Galli holds positions at both the U.S. Department of Energy’s Argonne National Laboratory and the University of Chicago Pritzker School of Molecular Engineering and Department of Chemistry. The research was published in the Journal of the American Chemical Society and supported by Q-NEXT, a DOE National Quantum Information Science Research Center led by Argonne.
Traditionally, researchers have created different materials for molecular qubits and tested their performance experimentally. The new method provides guidelines on designing these materials computationally before physical testing.
“From a design perspective, we wanted to come up with rules to engineer different properties of qubits that are beneficial to our specific application, whether that's quantum communication, quantum sensing or quantum computing,” said Michael Toriyama, postdoctoral researcher at Argonne. “Through our work, we developed a fully computational method to figure out these engineering principles.”
Molecular qubits rely on atomic spin states that can be manipulated for information processing. Accurate knowledge and control over ZFS values are necessary for precise operation in large-scale quantum systems.
“We can predict the coherence time from the ZFS using our methods, enabling better design principles to extend the coherence of a qubit,” Toriyama explained. “It's like we're figuring out how to build better armor around the qubit to protect it.”
The research team identified two main factors affecting ZFS: the geometry of the crystal surrounding the chromium atom and electric fields generated by the crystal's chemical composition.
“In other qubit types, like diamond, for example, there are limited possibilities for modifications, whereas with molecules there is a lot you can do. You can tune properties to the application you need,” said Diego Sorbelli from University of Perugia and former postdoctoral researcher at UChicago.
Lorenzo Baldinelli from University of Perugia added: “We give new design rules for modifying the composition of the environment to actively manipulate these spin structures, which we can accurately predict. So now, using our protocol, we can account not only for the electronic and spin properties of the qubit but also its surroundings.”
Sorbelli noted that predicting these properties from first principles was complex but made possible through collaboration between chemists, materials scientists and physicists within Galli’s group.
“Not too many groups are equipped to compute coherence properties of qubits. We leveraged the tools that our group has developed through years and years of research,” Toriyama said. “This was really a testament to how successful collaborations can be and how versatile our group is.”
This project received support from Q-NEXT under the U.S. Department of Energy Office of Science National Quantum Information Science Research Centers program.