Creating and Controlling Spin Qubits Through Molecular Engineering

Spin-based defects within semiconductors are used to construct devices that enable information processing and sensing technologies based on the quantum nature of electrons and atomic nuclei [1]. These systems have attracted interest as they possess an electronic spin state that can be employed as a quantum bit over a range of temperatures. They have a built-in optical interface in the visible and telecom bands, retain their quantum properties over millisecond timescales or longer, and can be manipulated using a simple combination of light and microwaves. In a complementary approach, molecular spin systems are attractive building blocks for quantum information science. Bottom-up chemical design of qubits can enable atomistic tunability of spin and optical properties, scalability to multi-qubit architectures, and modularity between various host materials and devices. Designer qubits could be synthesized for a diverse range of applications from quantum sensing in biosystems to the creation of nodes in a quantum network. To this end, we discuss organometallic molecular ground-state spins with optical addressability [2]. These molecules comprise a central spin-bearing metal ion coordinated to surrounding ligands, enabling optical initialization and read out, as well as coherent microwave manipulation of the ground-state spin. We also show atomistic tunability of qubit properties by comparing molecules which differ by the placement of a single methyl group on the coordinating ligands [3], the role of lattice symmetry in controlling coherence [4] and highlighting how molecular qubits can be tailored to enhance the coupling of spins to photons.<br/><br/>[1] C. P. Anderson, D. D. Awschalom, Physics Today 76, 26 (2023)<br/>[2] S.L. Bayliss, D.W. Laorenza et al., Science 370, 1309 (2020)<br/>[3] D.W. Laorenza, et al., JCAS 143, 50 (2021)<br/>[4] S.L. Bayliss, P. Deb et al., Phys. Rev. X 12, 031028 (2022)