# Spectroscopy of a synthetic trapped ion qubit

## TL;DR

This paper reports the spectroscopic characterization of the synthetic $^{133}$Ba$^+$ ion, including isotope shifts and hyperfine structure, to facilitate its use as a qubit in quantum information processing.

## Contribution

It provides the first detailed spectroscopic measurements of $^{133}$Ba$^+$, enabling laser cooling and quantum control of this isotope for quantum computing applications.

## Key findings

- Measured isotope shifts and hyperfine structures of key electronic transitions.
- Completed spectroscopic data for laser cooling all long-lived barium II isotopes.
- Demonstrated trapping and laser cooling of synthetic $^{133}$Ba$^+$.

## Abstract

$^{133}\text{Ba}^+$ has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1/2 nucleus and visible wavelength electronic transitions. Using a microgram source of radioactive material, we trap and laser-cool the synthetic $A$ = 133 radioisotope of barium II in a radio-frequency ion trap. Using the same, single trapped atom, we measure the isotope shifts and hyperfine structure of the $6^2 \text{P}_{1/2}$ $\leftrightarrow$ $6^2 \text{S}_{1/2}$ and $6^2 \text{P}_{1/2}$ $\leftrightarrow$ $5^2 \text{D}_{3/2}$ electronic transitions that are needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. We also report the $6^2 \text{P}_{1/2}$ $\leftrightarrow$ $5^2 \text{D}_{3/2}$ electronic transition isotope shift for the rare $A$ = 130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.