Cryogenic ion trap of ⁸⁸Sr⁺ with a superconductive helical RF resonator

Cryogenic ion trap is a crucial technique for implementing high-fidelity quantum logic gates with planer circuit traps. When a trap apparatus is cooled to a few kelvins, a motional decoherence caused by electric noise from the electrodes, known as the anomalous heating [1], can be suppressed. It is necessary to apply RF voltages higher than 100 V on the trap to levitate ions, while managing heat production inside the cryostat to maintain the cryogenic environment. To minimize the trapping RF power, we have developed a superconductive helical RF resonator, which is made from copper plated with lead. The skin of the resonator became superconducting below 7.2 K, and its quality factor reached 10⁴. Combined with a non-superconductive electrode trap, trapping of ⁸⁸Sr⁺ ions has been achieved with an RF power below +5 dBm.

[1] M. Brownnutt et al., Rev. Mod. Phys. 87, 1419 (2015).