Progress on PTB’s transportable Al+ ion clock

Optical atomic clocks achieve fractional systematic and statistical frequency uncertainties on the order of 10⁻¹⁸. This enables novel applications, such as height measurements in relativistic geodesy with ∼ 1 cm resolution for earth monitoring. Towards this goal, we set up a transportable clock based on the ¹S₀ → ³P₀ transition in ²⁷Al⁺. A co-trapped ⁴⁰Ca⁺ ion allows state detection and cooling via quantum logic spectroscopy and sympathetic cooling.
We unveil the design and the current status of the transportable apparatus and review the recent development of the laser systems. In particular, we present the clock laser setup emitting at 267.4 nm based on single-pass frequency-quadrupling which allows phase stabilization of the complete path. Furthermore, we show the performance of the fundamental frequency to reach a fractional frequency uncertainty of ~ 10⁻¹⁶ at 1 s.