The International Space Station provides an ideal platform for high precision frequency measurements, both as applied to scientific experiments and as regards basic time metrology. Consequently, a variety of clocks are being developed for flight on the Space Station, a majority of which are atomic clocks with very good stability for time periods in excess of 1,000 seconds. We plan to significantly augment the scope and capability of the ensemble of space clocks by adding to it SUperconducting Microwave Oscillator, SUMO. SUMO is a space version of the superconducting cavity stabilized oscillator, SCSO; the most precise clock developed to date for the interval range of around 100seconds. Short descriptions are given of the SUMO project and the SCSO technology and the principal disturbances causing frequency fluctuations are outlined. The planned improvements to the SCSO and preliminary results of the development work for SUMO are also highlighted.
The International Space Station provides an ideal platform for high precision frequency measurements, both as applied to scientific experiments and as regards basic time metrology. Consequently, a variety of clocks are being developed for flight on the Space Station, a majority of which are atomic clocks with very good stability for time periods in excess of 1,000 seconds. We plan to significantly augment the scope and capability of the ensemble of space clocks by adding to it SUperconducting Microwave Oscillator, SUMO. SUMO is a space version of the superconducting cavity stabilized oscillator, SCSO; the most precise clock developed to date for the interval range of around 100seconds. Short descriptions are given of the SUMO project and the SCSO technology and the principal disturbances causing frequency fluctuations are outlined. The planned improvements to the SCSO and preliminary results of the development work for SUMO are also highlighted.
Many physics experiments call on improved resolution to better define the experimental results, thus improving tests of theories. Modern microwave technology combined with high-Q resonators can achieve frequency readout and control with resolutions up to a part in 10(exp 18). When the physical quantity in question in the experiment can be converted to a frequency or a change in frequency, a high-stability microwave oscillator can be applied to obtain state-of-the-art precision. In this work we describe the overall physical concepts and the required experimental procedures for optimizing a high-resolution frequency measurement system that employs a high-Q superconducting microwave cavity and a low-noise frequency synthesizer. The basic approach is to resolve the resonant frequencies of a high-Q (Q > 10(exp 10)) cavity to extremely high precision (one part in 10(exp 17)- 10(exp 18)). Techniques for locking the synthesizer frequency to a resonant frequency of the superconducting cavity to form an ultra-stable oscillator are described. We have recently set up an ultra-high-vacuum high-temperature annealing system to process superconducting niobium cavities, and have been able to consistently achieve Q > 10(exp 9). We have integrated high-Q superconducting cavities with a low-noise microwave synthesizer in a phase-locked-loop to verify the frequency stability of the system. Effects that disturb the cavity resonant frequency (such as the temperature fluctuations and mechanical vibrations) and methods to mitigate those effects are also considered. Applicability of these techniques to experiments will be discussed, and our latest experimental progress in achieving high-resolution frequency measurements using the superconducting-cavity-stabilized-oscillator will be presented.
Abstract Atomic clocks with higher frequency stability and accuracy than traditional space-borne atomic clocks are the cornerstone of long-term autonomous operation of space-time-frequency systems. We proposed a space cold atoms clock based on an intracavity cooling scheme, which captures cold atoms at the center of a microwave cavity and then executes in situ interactions between the cold atoms and microwaves. As a result of the microgravity environment in space, the cold atoms can interact with the microwaves for a longer time, which aids in realizing a high-precision atomic clock in space. This paper presents the overall design, operational characteristics, and reliability test results of the space atomic clock based on the intracavity cooling scheme designed for the operation onboard the China space station. In addition, the engineering prototype performance of the space cold atoms microwave clock is also presented. The ground test results for the clock show a fractional frequency stability of 1.1 × 10−12 τ−1/2 reaching 2.5 × 10−15 at 200,000 s, providing solid technical and data support for its future operation in orbit.
Ultra-precise optical clocks in space will allow new studies in fundamental physics and astronomy. Within an European Space Agency (ESA) program, the “Space Optical Clocks” (SOC) project aims to install and to operate an optical lattice clock on the International Space Station (ISS) towards the end of this decade. It would be 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. Within the EU-FP7-SPACE-2010-1 project No. 263500, during the years 2011–2015 a compact, a modular and robust strontium lattice optical clock demonstrator has been developed. The goal performance is a fractional frequency instability below 1 × 10 − 15 τ − 1 / 2 and a fractional inaccuracy below 5 × 10 − 17 . Here we describe the current status of the apparatus' development, including the laser subsystems. The robust preparation of cold 88 Sr atoms in a second-stage magneto-optical trap (MOT) is achieved.
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 1×10−15at 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.
This work presents the realisation and characterisation of the world’s smallest transportable optical lattice clock as part of the Space Optical Clocks 2 EU project built at the University of Birmingham. Housed in a transportable rack of dimensions 170 x 100 x 60 cm, such a device aims to measure the frequency of the doubly-forbidden 1S0−3P0 clock transition in 88Sr in an unprecedented compact apparatus as a major technological milestone towards an optical clock upon the International Space Station. A master optical clock in space would serve with unrivalled accuracy and stability to disseminate a precise and accurate reference for terrestrial clocks and the coordination of international time. Such a clock has the potential to redefine the second, revolutionise timekeeping and precision measurements, and perform fundamental science experiments in space. \nUsing a combination of novel design, innovative cooling techniques, and robust, compact commercially available products, the clock portability, robustness and operational simplicity have been improved. The apparatus simply and effectively cools and traps up to 105 88Sr atoms at a temperature of 1.3±0.2μK in an optical lattice with a lifetime of 0.52±0.01s within 400ms. The most recent preliminary clock spectroscopy measurement was 3.6 ± 0.2Hz. The instability of the clock has been measured at 8×10−17 after averaging for 300s with the goal instability being 5.8×10−17 within the same averaging time. These results show the experiment will lead transportable optical clock research and continue with the goal of being a master clock in space.
With timekeeping being of paramount importance for modern life, much research and major scientific advances have been undertaken in the field of frequency metrology, particularly over the last few years. New Nobel-prize winning technologies have enabled a new era of atomic clocks; namely the optical clock. These have been shown to perform significantly better than the best microwave clocks reaching an inaccuracy of 1.6 10^-18. With such results being found in large lab based apparatus, the focus now has shifted to portability - to enable the accuracy of various ground based clocks to be measured, and compact autonomous performance - to enable such technologies to be tested in space. This could lead to a master clock in space, improving not only the accuracy of technologies on which modern life has come to require such as GPS and communication networks. But also more fundamentally, this could lead to the redefinition of the second and tests of fundamental physics. Within the European collaboration, Space Optical Clocks (SOC2) consisting of various institutes and industry partners across Europe we have tried to tackle this problem of miniaturisation whilst maintaining stability, accuracy (5 10^-17) and robustness whilst keeping power consumption to a minimum -- necessary for space applications. We will present the most recent results of the Sr optical clock in SOC2 and also the novel compact design features, new methods employed and outlook.