Chiral Geometric Qubit in a Frustrated Molecular Spin Triangle

Abstract

Spin frustration in antiferromagnetically coupled triangles creates states distinguished by chirality, offering a molecular route to encoded quantum operations. Here, we show how scalar chirality and geometric phases arise in the ground doublet of a spin-$1/2$ triangle. A Dzyaloshinskii--Moriya (DM) interaction establishes the chirality of the states, while broken $C_3$ symmetry allows these states to acquire geometric phases. We show how to encode a qubit in states of opposite scalar chirality and opposite geometric phases and implement a geometric $Z$ gate that cancels the relative dynamical phase, making it insensitive to pulse-duration errors. As an example of such a chiral geometric qubit, we investigate a Cu${}_3$-based paramagnetic molecular magnet, using broken-symmetry density functional theory and multireference spin--orbit calculations to estimate the strengths of the exchange and DM interactions. The results show that such paramagnetic molecules could serve as tunable platforms for implementing chiral geometric qubits.