Excitation of Molecular Hyperfine States with Electric-field Gradients

Molecular ions offer appealing architectures for quantum metrology and computing since their complex energy structures offer couplings over a wide range of the electromagnetic spectrum to the motional modes of an ion trap. Of particular interest are the addressable states within the radio-frequency to microwave region which in several species can be driven as electric dipole transitions, excluding the need for lasers. By generating electric-field gradients using the ion trap electrodes, the narrow linewidth transitions can be leveraged to perform non-destructive readout measurements as well as single and two-qubit gates (Phys. Rev. A 2021, 104, 042605). To demonstrate this technique, we co-trap Ca+ and HCl+ in a cryogenic ion trap, performing non-destructive readout of transitions between opposite parity hyperfine states of HCl+.