The reproducibility of spectral lines from atoms and ions makes them universally reliable frequency standards. Thus, improving the stability of ion traps is an open challenge in time and frequency metrology. A device invented by Stark et al. combines a radio-frequency cavity with a linear Paul trap to attain a remarkable standard of stability.

The researchers achieved this by minimizing two common ion trap problems: electromagnetic noise and spectral impurity of electric trapping fields. Their trap enclosure is made of niobium, which when cooled to its superconducting state, shields ions from external electric and magnetic fluctuations. Moreover, its geometry selectively amplifies and purifies the radio-frequency voltages needed for trapping. Working at 4.1 Kelvin with a cryogenic trap pressure below 10−14 millibar, the quality factor of the resonant cavity reaches values exceeding 200,000.

These features make the device a versatile, ultralow-noise trap capable of holding and cooling any ion at nearly ideal conditions, even highly charged ions, which have the highest frequency stability of any atomic system.

“This will prove an advantage … in searches for new fundamental physics that would manifest themselves as reproducible, very small deviations from the known laws of physics,” author Julian Stark said.

Optical clocks and quantum computers are some of the technological applications Stark anticipates of the device.

“As we speak, the next generation of optical clocks based on highly charged ions is being developed in our collaboration with the German national time-keeping institution, the Physikalisch-Technische Bundesanstalt,” he said. “Plans are coming up for using such traps for quantum-computing applications benefiting from its ultimate stability by keeping quantum error rates very low.”

Source: “An ultralow-noise superconducting radio-frequency ion trap for frequency metrology with highly charged ions,” by J. Stark, C. Warnecke, S. Bogen, S. Chen, E. A. Dijck, S. Kühn, M. K. Rosner, A. Graf, J. Nauta, J.-H. Oelmann, L. Schmöger, M. Schwarz, D. Liebert, L. J. Spieß, S. A. King, T. Leopold, P. Micke, P. O. Schmidt, T. Pfeifer, and J. R. Crespo Lopez-Urrutia, Review of Scientific Instruments (2021). The article can be accessed at https://doi.org/10.1063/5.0046569.