Development of a strontium optical lattice clock for the SOC mission on the ISS

Stefano Origlia ,P Gill,W Ertmer,M S Pramod,U Sterr,S Schiller,S Bize,E.-M Rasel,Ch Lisdat,Kai Bongs ,Lyndsie Smith ,Yeshpal Singh ,Sruthi Viswam ,Jérôme Lodewyck ,Bertrand Venon ,David Holleville ,Ian R Hill ,Wei He ,Dariusz Świerad ,J Stühler ,James W Hughes ,Yuri B Ovchinnikov ,Rodolphe Le Targat ,A P Kulosa ,G P Barwood ,Stefan Vogt ,Wilhelm Kaenders

doi:10.1117/12.2229473

Abstract

The ESA mission "Space Optical Clock" project aims at operating an optical lattice clock on the ISS in approximately 2023. The scientific goals of the mission are to perform tests of fundamental physics, to enable space-assisted relativistic geodesy and to intercompare optical clocks on the ground using microwave and optical links. The performance goal of the space clock is less than $1 \times 10^{-17}$ uncertainty and $1 \times 10^{-15} {\tau}^{-1/2}$ instability. Within an EU-FP7-funded project, a strontium optical lattice clock demonstrator has been developed. Goal performances are instability below $1 \times 10^{-15} {\tau}^{-1/2}$ and fractional inaccuracy $5 \times 10^{-17}$. For the design of the clock, techniques and approaches suitable for later space application are used, such as modular design, diode lasers, low power consumption subunits, and compact dimensions. The Sr clock apparatus is fully operational, and the clock transition in $^{88}$Sr was observed with linewidth as small as 9 Hz.

Highlights

The development of optical clocks worldwide is opening the door to new applications, with clocks on ground and in space
One current focus is transportable optical clocks. They are desirable for several reasons, such as comparisons between frequency standards in distant laboratories and for relativistic geodesy, and they represent an essential step towards space optical clocks
The system is fully operational using the isotopic species 88Sr. It is the choice for initial work, since it is the most abundant strontium isotope and easier to trap and cool, whereas 87Sr is preferred as optical frequency standard

Summary

INTRODUCTION

The development of optical clocks worldwide is opening the door to new applications, with clocks on ground and in space. The most recent results in the field of optical clocks show that uncertainty and instability approaching 1 × 10-18 has been achieved in neutral strontium[1] and ytterbium[2] clocks. One current focus is transportable optical clocks. Within the Space Optical Clock[3] (SOC) mission development two transportable optical lattice clocks have been built, based on neutral ytterbium[4] and strontium atoms. An even narrower linewidth (9 Hz) was achieved by locking the clock laser to a non-transportable ultrastable cavity. This first section of this report will introduce the applications of atomic clocks in space and the Space Optical Clock project, as well as the basics of a strontium optical lattice clock.

Space clocks applications

Strontium lattice clocks

THE SOC2 STRONTIUM BREADBOARD

Laser systems

Atoms cooling and trapping

Clock spectroscopy in the optical lattice

CONCLUSIONS