Fast state preparation and measurement of the ¹³³Ba⁺ ion qubits

We demonstrate fast, high-fidelity state preparation and measurement of a single trapped ¹³³Ba⁺ ion, a radioactive alkaline-earth ion with nuclear spin I=1/2, a long-lived $D_{5/2}$ state, and predominantly visible-wavelength optical transitions. This level structure enables simultaneous implementation of hyperfine and optical qubits within the same ion. We can efficiently load this ion to a radiofrequency  Paul trap by visible light photoionization. Using microwave-driven transitions within the $S_{1/2}$ hyperfine manifold, we coherently manipulate the hyperfine qubit with high precision. For state readout, the hyperfine qubit state is mapped onto the metastable $D_{5/2}$ manifold using 455 nm optical shelving, allowing discrimination of the qubit state via fluorescence detection. Off-resonant excitation from the shelving laser limits the readout fidelity; to mitigate this effect, we implement additional optical transfer pulses at 1762 nm addressing different hyperfine levels, significantly improving state-measurement performance. Composite pulse sequences are further employed to suppress amplitude and detuning errors in both microwave and optical control. These results establish ¹³³Ba⁺ as a promising platform for fast, high-fidelity qubit control, with applications to future entangling-gate experiments enabled by integrated photonics, which we are also actively testing.