The space optical clocks project: Development of high-performance transportable and breadboard optical clocks and advanced subsystems

Abstract

Abstract-The use of ultra-precise optical clocks in space ("master clocks") will allow for a range of new applications in the fields of fundamental physics (tests of Einstein's theory of General Relativity, time and frequency metrology by means of the comparison of distant terrestrial clocks), geophysics (mapping of the gravitational potential of Earth), and astronomy (providing local oscillators for radio ranging and interferometry in space). Within the ELIPS-3 program of ESA, the "Space Optical Clocks" (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade, as a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Undertaking a necessary step towards optical clocks in space, the EU-FP7-SPACE-2010-1 project no. 263500 (SOC2) (2011-2015) aims at two "engineering confidence", accurate transportable lattice optical clock demonstrators having relative frequency instability below 1×10 -15 at 1 s integration time and relative inaccuracy below 5×10 -17 . This goal performance is about 2 and 1 orders better in instability and inaccuracy, respectively, than today's best transportable clocks. The devices will be based on trapped neutral ytterbium and strontium atoms. One device will be a breadboard. The two systems will be validated in laboratory environments and their performance will be established by comparison with laboratory optical clocks and primary frequency standards. In order to achieve the goals, SOC2 will develop the necessary laser systems -adapted in terms of power, linewidth, frequency stability, long-term reliability, and accuracy. Novel solutions with reduced space, power and mass requirements will be implemented. Some of the laser systems will be developed towards particularly high compactness and robustness levels. Also, the project will validate crucial laser components in relevant environments. In this paper we present the project and the results achieved during the first year.

Towards practical autonomous deep-space navigation using X-Ray pulsar timing

“…For example, a space optical clock similar to those currently under development (e.g. [67]), could be of benefit to a long-duration advanced space experiment.…”

A compact atomic beam based system for Doppler-free laser spectroscopy of strontium atoms

“…Sr based clocks have reached fractional stability of 2.2 × 10 −16 and a total uncertainty of 2.1 × 10 −18 [1]. Efforts are also going on in building next generation space based optical clocks for fundamental physics, geophysics and astronomical applications [2,3]. For any such frequency reference to become a frequency standard, a large network of terrestrial and space based clocks is desirable leading to many technical challenges.…”

A compact, robust, and transportable ultra-stable laser with a fractional frequency instability of 1 × 10−15

“…These conditions make Space an ideal place to carry out certain precision experiments, in particular for testing fundamental notions of space and time [1][2][3][4][5][6]. For example, atomic clocks, including optical clocks, are proposed to be operated in Space for testing the gravitational time dilation or the Shapiro effect.…”