High-fidelity spatial and polarization addressing of Ca + 43 qubits using near-field microwave control
Individual addressing of qubits is essential for scalable quantum computation. Spatial addressing allows unlimited numbers of qubits to share the same frequency, while enabling arbitrary parallel operations. We demonstrate addressing of long-lived Ca+43 "atomic clock" qubits held in separate zones (960μm apart) of a microfabricated surface trap with integrated microwave electrodes. Such zones could form part of a "quantum charge-coupled device" architecture for a large-scale quantum information processor. By coherently canceling the microwave field in one zone we measure a ratio of Rabi frequencies between addressed and nonaddressed qubits of up to 1400, from which we calculate a spin-flip probability on the qubit transition of the nonaddressed ion of 1.3×10-6. Off-resonant excitation then becomes the dominant error process, at around 5×10-3. It can be prevented either by working at higher magnetic field, or by polarization control of the microwave field. We implement polarization control with error 2×10-5, which would suffice to suppress off-resonant excitation to the ∼10-9 level if combined with spatial addressing. Such polarization control could also enable fast microwave operations.