Axial and Radial Sympathetic Cooling in a Sorted Mixed-Isotope Ion Chain

Heating due to coupling to noisy electric field presents challenges to scaling up quantum systems based on long chains of trapped ions [1]. While motional heating can be countered by sympathetic cooling with other ion species, it is challenging to do this in long chains while preserving qubit coherence and connectivity. We address this challenge by sympathetically cooling ¹⁷¹Yb⁺ data ions with ¹⁷²Yb⁺ ions [1].

Collisions with background gas atoms cause reordering of the two isotopes in our room-temperature chains, which affects the operation of entangling gates. We maintain the isotope sequence of ions trapped in a Sandia HOA 2.1.1 surface trap [2] using an efficient sorting protocol using nearest-neighbor swaps with low overhead. We implement sympathetic narrow-line cooling on both axial and radial modes of sorted mixed-species chains and investigate the resulting cross-thermalization of the modes.