The team wanted to find a new bottom-up approach to develop molecules whose spin states can be used as qubits, and can be readily interfaced with the outside world. To do so, they used organometallic chromium molecules to create a spin state that they could control with light and microwaves.
By exciting the molecules with precisely controlled laser pulses and measuring the light emitted, they could “read” the molecules’ spin state after being placed in a superposition—a key requirement for using them in quantum technologies
By varying just a few different atoms on these molecules through synthetic chemistry, they were also able to modify both their optical and magnetic properties, highlighting the promise for tailor-made molecular qubits.
“Over the last few decades, optically addressable spins in semiconductors have been shown to be extremely powerful for applications including quantum-enhanced sensing,” said Awschalom, who is also director of the Chicago Quantum Exchange and director of Q-NEXT, a Department of Energy National Quantum Information Science Research Center led by Argonne National Laboratory. “Translating the physics of these systems into a molecular architecture opens a powerful toolbox of synthetic chemistry to enable novel functionality that we are only just beginning to explore.”
“Our results open up a new area of synthetic chemistry. We demonstrated that synthetic control of symmetry and bonding creates qubits that can be addressed in the same way as defects in semiconductors,” Freedman said. “Our bottom-up approach enables both functionalization of individual units as ‘designer qubits’ for target applications and the creation of arrays of readily controllable quantum states, offering the possibility of scalable quantum systems.”
One potential application for these molecules could be quantum sensors that are designed to target specific molecules. Such sensors could find specific cells within the body, detect when food spoils, or even spot dangerous chemicals.
This bottom-up approach could also help integrate quantum technologies with existing classical technologies.
“Some of the challenges facing quantum technologies might be able to be overcome with this very different bottom-up approach,” said Sam Bayliss, a postdoctoral scholar in the Awschalom Group at University of Chicago’s Pritzker School of Molecular Engineering and co first author on the paper. “Using molecular systems in light-emitting diodes was a transformative shift; perhaps something similar could happen with molecular qubits.”
Daniel Laorenza, a graduate student at Northwestern University and co-first author, sees tremendous potential for chemical innovation in this space. “This chemically specific control over the environment around the qubit provides a valuable feature to integrate optically addressable molecular qubits into a wide range of environments,” he said.
Other authors on the paper include UChicago graduate students Peter Mintun and Berk Diler Kovos.
Citation: “Optically addressable molecular spins for quantum information processing.” Bayliss et al., Science, Nov. 12, 2020. DOI: 10.1126/science.abb9352
Funding: Office of Naval Research, National Science Foundation, Department of Energy