Towards a Transportable Aluminium Ion Quantum Logic Optical Clock

Abstract

With the advent of optical clocks featuring fractional frequency uncertainties on the order of $10^{-17}$ and below, new applications such as chronometric levelling with few-cm height resolution emerge. We are developing a transportable optical clock based on a single trapped aluminium 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 ${}^{40}{\mathrm{Ca}}^{+}$. Important features are a segmented multi-layer 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 ${}^{40}{\mathrm{Ca}}^{+}$ repump laser system. We present preliminary estimates of the trap-induced frequency shifts on ${}^{27}{\mathrm{Al}}^{+}$, derived from measurements with a single calcium ion. The micromotion-induced second-order Doppler shift for ${}^{27}{\mathrm{Al}}^{+}$ has been determined to be \sods and the black-body radiation shift is $\hat{I}´\hat{I}{½}_{\mathrm{BBR}}/\hat{I}½=(-4.0\pm 0.4)\times 10^{-18}$. Moreover, heating rates of 30 (7) quanta per second at trap frequencies of $\ddot{I}{‰}_{\mathrm{rad},\mathrm{Ca}+}\approx 2\ddot{I}€\times 2.5\mathrm{MHz}$ ($\ddot{I}{‰}_{\mathrm{ax},\mathrm{Ca}+}\approx 2\ddot{I}€\times 1.5\mathrm{MHz}$) in radial (axial) direction have been measured, enabling interrogation times of a few hundreds of milliseconds.

14 pages, 17 figures