European Conference on Trapped Ions (ECTI)

Highly charged ions (HCI) offer promising candidate species for searches of physics beyond the Standard Model and next-generation optical atomic clocks. In the CryPTEx-SC experiment, we store HCIs in a cryogenic linear Paul trap that simultaneously functions as a superconducting radio-frequency resonator filtering the trap drive [1].
The HCIs are produced in a compact electron beam ion trap and then injected into and sympathetically cooled by a Coulomb crystal of Be${}^{+}$ ions. Subsequently removing ions until a single Be${}^{+}$ cooling ion and a single HCI are left enables quantum logic spectroscopy towards frequency metrology and qubit operations with a great variety of species.
We present Be${}^{+}$ microwave spectroscopy measurements characterizing the magnetic shielding properties of the resonator trap built from superconducting niobium that almost fully encloses the stored ions [2]. While cooling the resonator trap down through its transition temperature into the superconducting state, a quantization magnetic field applied at this time becomes persistent and the trap becomes shielded from subsequent external electromagnetic fluctuations.
Using a magnetically-sensitive hyperfine transition of Be${}^{+}$ as probe, we measure the fractional decay rate of the stored magnetic field to be at the 10${}^{-10}$ s${}^{-1}$ level. Ramsey interferometry and spin-echo measurements yield coherence times of over 400 ms without active field stabilization, demonstrating excellent passive shielding of magnetic field noise at frequencies down to DC, producing a suitable environment for precision ion spectroscopy.
[1] Stark et al., Rev. Sci. Instrum. 92, 083203 (2021)
[2] Dijck et al., arXiv:2306.01670, to appear in Rev. Sci. Instrum. (2023)