ABaQuS: A trapped-ion quantum computing system using ¹³³Ba⁺qubits

We present the design of a trapped-ion quantum computing system based on ¹³³Ba⁺ ions. The ¹³³Ba⁺ ions offer a range of potential qubit states, including magnetically insensitive hyperfine ‘clock’ qubits in the ground level and in the metastable D_5/2 level, and optical ‘clock’ qubits spanning the S_1/2−D_5/2 manifolds, therefore offering an interesting playground for novel qubit addressing, qubit hiding, and laser cooling schemes. The ion's visible light optical transitions [1] allow for the use of off-the-shelf laser components such as high performance fibre-based optical modulators.

In our experiment the ¹³³Ba⁺ ions are confined in a monolithic 3D microfabricated trap [2] that provides a high degree of control of the trapping potential whilst maintaining a low heating rate. The ground level qubit transition is driven by a two-photon Raman process using a 532 nm laser. We present our novel system for driving this 10 GHz qubit transition with low phase and intensity noise. We further discuss the design of a laser-written waveguide device used for individual addressing of non-uniformly spaced ion crystals.

[1] J. E. Christensen, D. Hucul, W. C. Campbell, and E. R. Hudson. High-fidelity manipulation of a qubit enabled by a manufactured nucleus. npj Quantum Information, 6(1):35, 2020.

[2] P. See, G. Wilpers, P. Gill, and A. G. Sinclair. Fabrication of a monolithicarray of three dimensional si-based ion traps. Journal of Microelectromechanical Systems, 22(5):1180–1189, 2013.