Towards motional mode engineering in a long trapped ion string using optical tweezers

Long linear trapped ion crystals are a well established platform for quantum information processing and quantum simulations. Performing high fidelity gate operations which rely on shared phonon modes becomes challenging due to spectral crowding and motional heating. Parallel gate operations become especially difficult due to the collective nature of phonon modes. These challenges can be mitigated by engineering the trapping potentials along the string locally to decouple the motion of selected ions from the collective. Selectively increasing confinement at specific ions can be used to create local motional modes. This also increases the frequency of the common motional mode, which results in a reduction of motional heating to allow for higher gate fidelity.

We present experimental work performed in a cryogenic apparatus exploiting a segmented-electrode ion trap architecture. This provides an ultra-high vacuum environment and fine control over the electric trapping potentials, allowing us to produce stable long linear ion strings.

A subset of up to ten ions are individually controlled by tightly focused laser beams perpendicular to the ion string axis providing reconfigurable optical tweezers and single ion addressing for quantum operations. We demonstrate engineering of the motional spectrum of long ion strings of up to a hundred ⁴⁰Ca⁺ ions.