image: Figure 1: (Left) Rotation and acceleration measurements using the CSSAI in-orbit and (Right) Rotation comparison between the CSSAI and the classical gyroscopes of the CSS.
Credit: ©Science China Press
High-precision space-based gyroscopes are important in space science research and space engineering applications. In fundamental physics research, they can be used to test the general relativity effects, such as the frame-dragging effect. These tests can explore the boundaries of the validity of general relativity and search for potential new physical theories. Several satellite projects have been implemented, including the Gravity Probe B (GP-B) and the Laser Relativity Satellite (LARES), which used electrostatic gyroscopes or the orbit data of the satellite to test the frame-dragging effect, achieving testing accuracies of 19% and 3% respectively. No violation of this general relativity effect was observed. Atom interferometers (AIs) use matter waves to measure inertial quantities. In space, thanks to the quiet satellite environment and long interference time, AIs are expected to achieve much higher acceleration and rotation measurement accuracies than those on the ground, making them important candidates for high-precision space-based inertial sensors. Europe and the United States propose relevant projects and have already conducted pre-research experiments for AIs using microgravity platforms such as the dropping tower, sounding rocket, parabolic flying plane, and the International Space Station.
The research team led by Mingsheng Zhan from the Innovation Academy for Precision Measurement Science and Technology of the Chinese Academy of Sciences (APM) developed a payload named China Space Station Atom Interferometer (CSSAI) [npj Microgravity 2023, 9 (58): 1-10], which was launched in November 2022 and installed inside the High Microgravity Level Research Rack in the China Space Station (CSS) to carry out scientific experiments. This payload enables atomic interference experiments of 85Rb and 87Rb and features an integrated design. The overall size of the payload is only 46 cm × 33 cm × 26 cm, with a maximum power consumption of approximately 75 W.
Recently, Zhan’s team used CSSAI to realize the space cold atom gyroscope measurements and systematically analyze its performance. Based on the 87Rb atomic shearing interference fringes achieved in orbit, the team analyzed the optimal shearing angle relationship to eliminate rotational measurement errors and proposed methods to calibrate these angles, realizing precise in-orbit rotation and acceleration measurements. The uncertainty of the rotational measurement is better than 3.0×10⁻⁵ rad/s, and the resolution of the acceleration measurement is better than 1.1×10⁻⁶ m/s². The team also revealed various errors that affect the space rotational measurements. This research provides a basis for the future development of high-precision space quantum inertial sensors. This work has been published in the 4th issue of National Science Review in 2025, titled "Realization of a cold atom gyroscope in space". Professors Xi Chen, Jin Wang, and Mingsheng Zhan are the co-corresponding authors.
The research team analyzed and solved the dephasing problem of the cold atom shearing interference fringe. Under general cases, the period and phase of shearing fringes will be affected by the initial position and velocity distribution of cold atom clouds, thus resulting in errors in rotation and acceleration measurements. Through detailed analyses of the phase of the shearing fringes, a magic shearing angle relationship was found, which eliminates the dephasing caused by the parameters of the atom clouds. Furthermore, a scheme was proposed to calibrate the shearing angle precisely in orbit. Then, the research team carried out precision in-orbit rotation and acceleration measurements based on the shearing interference fringes. By utilizing the fringes with an interference time of 75 ms, a rotation measurement resolution of 50 μrad/s and an acceleration measurement resolution of 1.0 μm/s² were achieved for a single experiment. A long-term rotation measurement resolution of 17 μrad/s was achieved through data integration. Furthermore, the research team studied error terms for the in-orbit atom interference rotation measurement. Systematic effects were analyzed for the imaging magnification factor, shearing angle, interference time sequence, laser wavelength, atom cloud parameter, magnetic field distribution, etc. It is found that the shearing angle error is one of the main factors that limits the measurement accuracy of future high-precision cold atom gyroscopes in space. The rotation measured by CSSAI was compared with that measured by the gyroscope of the CSS, and these two measurement values are in good agreement, further demonstrating the reliability of the rotation measurement.
This work not only realized the world's first space cold atom gyroscope but also provided foundations for the future space quantum inertial sensors in engineering design, inertial quantity extraction, and error evaluation.