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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.

Techniques developed for quantum-information processing using trapped ions may be useful in future atomic clocks. Here, we summarize experiments at NIST that (1) use quantum gates to entangle ions and thereby improve the measurement signal-to-noise ratio in spectroscopy and (2) implement sympathetic cooling and quantum state transfer techniques, which might be used to increase the number of choices of ions used for clocks.