Probing spin-electric transitions in a molecular exchange qubit

Electric fields represent an ideal means for controlling spins at the nanoscale. Here we perform low-temperature magnetic far-IR spectroscopy on a molecular spin triangle (Fe3), and provide the first experimental evidence of spin-electric transitions in polynuclear complexes. Based on spin Hamiltonian simulations of the spectra, we identify the observed transitions, estimate the value of the spin-electric coupling, and introduce the concept of generalized exchange qubit. This applies to a wide class of molecular spin triangles, and includes the scalar chirality and the partial spin sum qubits as special cases. Finally, we theoretically show that the polarization can be used to discriminate between electric- and magnetic-dipole transitions, as well as to identify the physical origin of the zero-field splitting in the ground multiplet, a debated issue with significant implications on the coherence properties of the exchange qubit implemented in molecular spin triangles.