# A cryogenic radio-frequency ion trap for quantum logic spectroscopy of highly charged ions

## TL;DR

This paper introduces a cryogenic RF ion trap system optimized for quantum logic spectroscopy of highly charged ions, demonstrating ground state cooling, low noise, and stable magnetic fields, enabling advanced ion trapping experiments.

## Contribution

The paper presents a novel cryogenic ion trap system capable of trapping and cooling highly charged ions alongside Be+ ions for quantum logic spectroscopy.

## Key findings

- Achieved ground state cooling of ion motion modes.
- Demonstrated low electric field noise levels.
- Successfully trapped and co-trapped highly charged Ar$^{13+}$ ions.

## Abstract

A cryogenic radio-frequency ion trap system designed for quantum logic spectroscopy of highly charged ions is presented. It includes a segmented linear Paul trap, an in-vacuum imaging lens and a helical resonator. We demonstrate ground state cooling of all three modes of motion of a single $^9$Be$^+$ ion and determine their heating rates as well as excess axial micromotion. The trap shows one of the lowest levels of electric field noise published to date. We investigate the magnetic-field noise suppression in cryogenic shields made from segmented copper, the resulting magnetic field stability at the ion position and the resulting coherence time. Using this trap in conjunction with an electron beam ion trap and a deceleration beamline, we have been able to trap single highly charged Ar$^{13+}$ (Ar XIV) ions concurrently with single Be$^+$ ions, a key prerequisite for the first quantum logic spectroscopy of a highly charged ion.