Molecular Quantum Logic Spectroscopy Using Electric-field Gradients*

Quantum-state-controlled molecular ions represent a new paradigm for the study of quantum information, metrology, and chemistry due to their extensive state space. Of particular interest are the electric dipole addressable states within the radio-frequency to microwave region. These narrow linewidth states allow for robust, laser-free quantum operations and can be implemented using electric field gradients generated by the trap electrodes (Phys. Rev. A 2021, 104, 042605). We demonstrate an example of this technique by performing a non-destructive readout of the hyperfine states of HCl+ co-trapped with Ca+. Spectroscopy is performed on opposite parity states between different hyperfine manifolds, within the same hyperfine manifold, and for different hydrogen nuclear spins.