Photogeneration and Control of Molecular Electron Spin Qubits for Quantum Information Science

In this project, funded by the Chemical Mechanism, Function, and Properties Program of the Chemistry Division, Professor Michael R. Wasielewski of the Department of Chemistry at Northwestern University is developing molecular quantum bits (qubits) for quantum information applications that offer a variety of benefits compared to other physical qubits, such as structural reproducibility, atomic scale spatial control, and structural modularity. Molecular architectures provide unmatched flexibility for tailoring quantum properties using bottom-up synthetic strategies. The project will use light to generate unpaired electron spins in molecules that will serve as good qubits because their two spin states constitute the quintessential two-level quantum system, in which the two states can exist in a superposition. The project will also study the interaction of two or more spins resulting in quantum entanglement, a property essential to most quantum information science applications in computing, communications and sensing. In addition, this project will provide the advanced education for students necessary for workforce development in the rapidly expanding field of quantum information science. Photogenerated spin-correlated radical pairs (SCRPs) in organic molecules provide new molecular approaches to spin qubit pairs (SQPs) for QIS applications. This project addresses four goals essential for exploiting SCRPs as SQPs that target QIS applications. The investigators will 1) photo-generate SCRPs doped into crystalline hosts to produce oriented SQPs with well-defined initial quantum states that will be addressed and manipulated using microwave pulses to serve as two-qubit quantum gates using optically detected magnetic resonance (pulse-ODMR) readout; 2) teleport spin states between two sites, focusing on a new approach that employs long-lived excited states of stable radicals to promote longer distance teleportation in systems doped into crystalline hosts; 3) explore how the degree of molecular chirality influences coherent spin dynamics through the chirality-induced spin selectivity (CISS) effect; and 4) investigate how CISS influences spin teleportation, and in turn, how teleportation can inform on the magnitude of the CISS contribution to spin dynamics. In topics 3 and 4, in addition to small molecules, they will employ DNA hairpins, which will provide a scalable platform for the rapid synthesis of a wide variety of molecular QIS systems. They will perform time resolved electron paramagnetic resonance experiments using continuous as well as pulsed microwaves following laser excitation of the molecules to create the SQPs. They will also employ pulse-ODMR to explore how to reduce the size of the spin ensembles with the ultimate goal of achieving single molecule or near single molecule sensitivity to probe the spin states of these systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.