### Description

Trapped ion devices make some of the best candidates for quantum information processors as they provide naturally identical qubits with long coherence times. One approach to scaling these systems is using large registers of ions. This can be achieved through implementing qubits in multiple atomic species, where each qubit type is insensitive to the others' light fields, eliminating scattering errors. This allows for advanced qubit control and manipulation schemes. However, using multiple species adds significant experimental overhead [1].

An alternative to using multiple species is using long lived metastable states to encode, store, and manipulate quantum information. In our experiment, we use Barium ions, which have a metastable $5\text{D}_{5/2}$ manifold with a lifetime of $\sim30\,\text{s}$, long enough for quantum information processing. When combined with the stable $6\text{S}_{1/2}$ ground state manifold, we can gain all of the benefits of having two atomic species, while maintaining the technical simplicity of having just one [1,2]. Additionally, the Barium isotope we use, $^{137}\text{Ba}^{+}$, has nuclear spin 3/2, giving magnetically insensitive ‘clock’ qubits in both the $6\text{S}_{1/2}$ and $5\text{D}_{5/2}$ manifolds as well as ‘clock’ transitions between the manifolds. Both the ground state qubits and metastable state qubits can be driven using a 2-photon Raman process with 532nm light and very low scattering error.

We demonstrate individual manipulation of ‘clock’ qubits in these separate manifolds, a prerequisite for partial projective measurements and mid-circuit measurements. Such techniques can be used for error correction schemes using ancilla qubits. Additionally, we can perform in-sequence cooling of the ions to keep error rates low and constant.

## References

[1] D. Allcock et al., Applied Physics Letters, vol. 119, p. 214 002, 2021.

[2] H.-X. Yang et al., arXiv preprint arXiv:2106.14906, 2021.

Presenter name | Jamie Leppard |
---|---|

How will you attend ICAP-27? | I am planning on in-person attendance |