Progress towards dipole-phonon quantum logic with trapped CaO⁺ and Ca⁺ ion

The rich internal structure of molecular ions provides challenges and opportunities for the control of molecular states for quantum information. Here we focus on dipole-phonon quantum logic, where the state of the molecular ion can be controlled through the coupling of the molecular ion dipole to its motion in an ion trap [1,2]. This requires the careful choice of a molecular ion with a dipole-allowed transition at typical ion trap frequencies. We have identified the L-doublet states of CaO+ as an ideal candidate with a predicted splitting of 0.45 MHz and 1.9 MHz for states |??²Π_3/2,??=0,??=3/2〉 and |??²Π_3/2,??=0,??=5/2〉 [3]. In our experiment, we trap a calcium oxide ion (CaO+) and a calcium ion (Ca+), where the Ca+ ion is used for sympathetic cooling and the readout of the phonon state. In this talk, we will report on the challenges of preparing CaO+ in the desired state and our latest progress towards observing dipole-phonon quantum logic.

[1] E. R. Hudson and W. C. Campbell, “Dipolar quantum logic for freely rotating trapped molecular ions,” Phys. Rev. A 98, 040302 (2018).

[2] W. C. Campbell and E. R. Hudson, “Dipole-phonon quantum logic with trapped polar molecular ions,” (2019), arXiv:1909.02668

[3] M. Mills, H. Wu, E. C. Reed, L. Qi, K. R. Brown, C. Schneider, M. C. Heaven, W. C. Campbell, and E. R. Hudson, “Dipole-phonon quantum logic with alkaline-earth monoxide and monosulfide cations,” Phys. Chem. Chem. Phys. 22, 24964–24973 (2020).