Heat management in ion trap optical clocks leads to extremely low uncertainties

Ion trap optical clocks measure time precisely using the energy of atomic transitions. They are so precise that black body radiation surrounding the ion is often one of the largest sources of uncertainty. This black body radiation comes primarily from heat generated by the high voltages oscillating in the megahertz range needed to operate the trap.

Nordmann et al. use passive heat management to design a trap constructed from aluminum nitride with very low, well-determined radiofrequency-induced heating and good passive heat dissipation. Using finite-element modeling and experimental measurements, the authors precisely characterize the temperature at the ions to report some of the lowest ever temperature-based uncertainties in trapped ion optical clocks operating at room temperature.

The researchers characterize the temperature of the traps by combining infrared imaging, in-situ sensors and numerical models of heat flow. “We have two sensors integrated into the trap,” said Nordmann. “We compared this to measurements with an infrared camera to see the temperature distribution across the trap. The model was adjusted until all measurements matched as closely as possible.” The model was then used with the two sensors to extract the temperature at the position of the ions.

Using this technique, the researchers achieve one of the smallest reported temperature uncertainties for ion traps, around 70 milliKelvins.

“At the moment, we are happy with the trap,” Nordmann said. However, further work is required to develop the trap into a working clock with multiple trapped ions. “We are about to demonstrate this in our trap, but it is not so easy,” she said. “That is really something nobody has done so far.”

Source: “Sub-kelvin temperature management in ion traps for optical clocks,” by T. Nordmann, A. Didier, M. Doležal, P. Balling, T. Burgermeister, and T. E. Mehlstäubler, Review of Scientific Instruments (2020). The article can be accessed at https://doi.org/10.1063/5.0024693 .