Towards a transportable aluminium ion quantum logic optical clock.

With the advent of optical clocks featuring fractional frequency uncertainties on the order of 10 and below, new applications such as chronometric leveling with few-centimeter height resolution emerge. We are developing a transportable optical clock based on a single trapped aluminum ion, which is interrogated via quantum logic spectroscopy. We employ singly charged calcium as the logic ion for sympathetic cooling, state preparation, and readout. Here, we present a simple and compact physics and laser package for manipulation of Ca. Important features are a segmented multilayer trap with separate loading and probing zones, a compact titanium vacuum chamber, a near-diffraction-limited imaging system with high numerical aperture based on a single biaspheric lens, and an all-in-fiber Ca repump laser system. We present preliminary estimates of the trap-induced frequency shifts on Al, derived from measurements with a single calcium ion. The micromotion-induced second-order Doppler shift for Al has been determined to be δνν=-0.4 ×10 and the black-body radiation shift is δν/ν = (-4.0 ± 0.4) × 10. Moreover, heating rates of 30 (7) quanta per second at trap frequencies of ω ≈ 2π × 2.5 MHz (ω ≈ 2π × 1.5 MHz) in radial (axial) direction have been measured, enabling interrogation times of a few hundreds of milliseconds.