# Ion-Based Characterization of Laser Beam Profiles for Quantum Information Processing

## TL;DR

This paper shows how trapped ions can be used to measure laser beam properties for quantum computing, improving gate performance.

## Contribution

A novel method using trapped ions as sensors to characterize laser beams for quantum gates is introduced.

## Key findings

- Using 171Yb+ ions, the four-photon Stark Shift effect is applied to measure laser profiles, alignments, and polarizations.
- Optimizing individual laser parameters leads to faster and more stable Raman-driven quantum gates.
- Trapped ions can effectively probe their local environment to improve system performance.

## Abstract

Laser-driven operations are a common approach for engineering one- and two-qubit gates in trapped-ion arrays. Measuring key parameters of these lasers, such as beam sizes, intensities, and polarizations, is central to predicting and optimizing gate speeds and stability. Unfortunately, it is challenging to accurately measure these properties at the ion location within an ultra-high vacuum chamber. Here, we demonstrate how the ions themselves may be used as sensors to directly characterize the laser beams needed for quantum gate operations. Making use of the four-photon Stark Shift effect in 171Yb+ ions, we measure the profiles, alignments, and polarizations of the lasers driving counter-propagating Raman transitions. We then show that optimizing the parameters of each laser individually leads to higher-speed Raman-driven gates with smaller susceptibility to errors. Our approach demonstrates the capability of trapped ions to probe their local environments and to provide useful feedback for improving system performance.