# Observation of individual spin quantum transitions of a single antiproton

## TL;DR

This paper reports the first detection of individual spin quantum transitions of a single trapped antiproton, demonstrating high-fidelity spin-state determination and initialization, advancing precision measurements of the antiproton magnetic moment.

## Contribution

It introduces a method for detecting single antiproton spin transitions with high fidelity in a Penning trap, enabling more precise magnetic moment measurements.

## Key findings

- Spin quantum transitions detected with 92.1% fidelity.
- Spin-state initialization achieved with >99.9% fidelity.
- Average initialization time of 24 minutes.

## Abstract

We report on the detection of individual spin quantum transitions of a single trapped antiproton in a Penning trap. The spin-state determination, which is based on the unambiguous detection of axial frequency shifts in presence of a strong magnetic bottle, reaches a fidelity of 92.1$\%$. Spin-state initialization with $>99.9\%$ fidelity and an average initialization time of 24 min are demonstrated. This is a major step towards an antiproton magnetic moment measurement with a relative uncertainty on the part-per-billion level.