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IEEE photonics journal

The Design, Realization, and Validation of the Scheme for Quantum Degenerate Research in Microgravity

Lin Li, Wei Xiong, Bin Wang, Tang Li, Y. Xie, Angang Liang, Mingshan Huang, Xiaolong Yuan, Yuanyuan Liu, Jingwei Ji, Min Gao, Minjie Huang, Cuiyun Zhou, Tieqiang Song, Xingping Xu, Zhaogang Liang, Su Fang, Dijun Chen, Xia Hou, Xiaoji Zhou, Xuzong Chen, Weibiao Chen, Liang Liu

Published Apr 10, 2023• 8 citations
Publisher

Abstract

In microgravity, atoms can be prepared to a lower temperature and manipulated with a longer time. The Cold Atom Physics Research Rack (CAPR) in Chinese Space Station, which aims to prepare quantum degenerate gas for deep cooling and quantum simulation in microgravity, has been designed, realized, and validated. We built an integrated CAPR, consisting of a physical system, an all-fiber 780nm laser system and a low phase noise 1064nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a87Rb quantum degenerate gas with 1.2ⅹ105atoms and a temperature below 30nK was achieved on ground. In this article, we also show the robustness of the rack, based on the experimental results before and after the simulation of the vibration and impact during the launch.

DOI
10.1109/jphot.2023.3266108

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In microgravity, atoms can be prepared to a lower temperature and manipulated with a longer time. The Cold Atom Physics Research Rack (CAPR) in Chinese Space Station, which aims to prepare quantum degenerate gas for deep cooling and quantum simulation in microgravity, has been designed, realized, and validated. We built an integrated CAPR, consisting of a physical system, an all-fiber 780nm laser system and a low phase noise 1064nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a87Rb quantum degenerate gas with 1.2ⅹ105atoms and a temperature below 30nK was achieved on ground. In this article, we also show the robustness of the rack, based on the experimental results before and after the simulation of the vibration and impact during the launch.
The Cold Atom Physics Rack (CAPR) of Chinese space station will be launched at the end of 2022. The important goal of CAPR is to achieve BEC at 100 pk. In order to obtain ultracold atoms in microgravity of space station, we propose a two-stage cooling scheme using all-optical trap with different waist beams. The cold atom cloud obtained by this scheme is composed of condensate and thermal atoms around condensate. The design of our two-stage cooling scheme will effectively reduce the temperature of the thermal atom cloud and the effective temperature generated by the interaction energy of the condensate. The atomic temperature of 5 nk is obtained from the ground test experiment, and the corresponding temperature under the microgravity condition of the space station is theoretically predicted to be less than 100 pk. Taking the advantages of ultracold temperature and long-time detection, many scientific experiments will be arranged. In this paper, the ground test experiments based on ground principle prototype and pre-prototype for CAPR are also introduced.
The China Space Station (CSS) provides an ideal experimental platform for researching and applying ultracold atoms in microgravity. On 31 October 2022, the Cold Atom Physics Research Rack (CAPR) was launched to the CSS together with the Mengtian lab module, designed by the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (SIOM) and Peking University. The main goal of the CAPR is to build an ultracold atomic physics experiment platform using 87Rb Bose Einstein Condensate (BEC) in the CSS. In microgravity, ultracold atoms can be cooled to picokelvin (pK) via Two-Stage Crossed Beams Cooling (TSCBC), which is three orders of magnitude lower than on earth and can inspire the novel physical phenomena. The preparation of the BEC and the deep cooling are introduced in this paper, as well as a series of advancements in ultracold atoms in microgravity. The CAPR is an experimental platform that relies on evaporative cooling in a crossed optical dipole trap. Furthermore, the CAPR’s design scheme and ground verification experiment are also introduced. So far, the CAPR has continued to conduct research on ultracold atoms in microgravity, with more than two years of uninterrupted operation in orbit. Up to now, preliminary experimental results have been achieved, realizing the primary purpose of the CAPR.
In the development of the Cold Atom Physics Research Rack (CAPR) on board the Chinese Space Station, the laser system plays a critical role in preparing the all-optical 87Rb Bose–Einstein condensates (BECs). An all-fiber laser system has been developed for CAPR to provide the required optical fields for atom interaction and to maintain the beam pointing in long-term operation. The laser system integrates a 780 nm fiber laser system and an all-fiber optical control module for sub-Doppler cooling, as well as an all-fiber 1064 nm laser system for evaporative cooling. The high-power, single-frequency 780 nm lasers are achieved through rare-Earth doped fiber amplification, fiber frequency-doubling, and frequency stabilization technology. The all-fiber optical control module divides the output of the 780 nm laser system into 15 channels and regulates them for cooling, trapping, and probing atoms. Moreover, the power consistency of each pair of cooling beams is ensured by three power tracking modules, which is a prerequisite for maintaining stable MOT and molasses. A high-power, compact, controlled-flexible, and highly stable l064 nm all-fiber laser system employing two-stage ytterbium-doped fiber amplifier (YDFA) technology has been designed for evaporative cooling in the optical dipole trap (ODT). Finally, an all-optical 87Rb BEC is realized with this all-fiber laser system, which provides an alternative solution for trapping and manipulating ultra-cold atoms in challenging environmental conditions.
To obtain cold atom samples with temperatures lower than 100 pK in the cold atom physics rack experiment of the Chinese Space Station, we propose to use the momentum filtering method for deep cooling of atoms.This paper introduces the experimental results of the momentum filtering method verified by our ground testing system.In the experiment, we designed a specific experimental sequence of standing-wave light pulses to control the temperature, atomic number, and size of the atomic cloud.The results show that the momentum filter can effectively and conveniently reduce the temperature of the atomic cloud and the energy of Bose-Einstein condensation, and can be flexibly combined with other cooling methods to enhance the cooling effect.This work provides a method for the atomic cooling scheme of the ultra-cold atomic system on the ground and on the space station, and shows a way of deep cooling atoms.
Cold atom states are prepared by laser cooling, evaporation cooling and other cooling methods to cool down the atoms close to almost absolute zero in temperature. As a popular research frontier of quantum physics, cold atom physics has been developed to explore, study and measure the spin degrees of freedom in atoms. The precise measurement of the rich quantum magnetism presented by the hyperfine structure of the internal spin freedom is undoubtedly of great significance to basic physics and the innovation of new technologies. With the advantages of microgravity environment and the creation of new extreme conditions, cold atom experimentalists can achieve long-time precision measurement and ultra-low temperature of pK level which is not viable on the ground. The manipulation and precision measurement of quantum magnetism can break through the gravitational limit and reach new parameter regions. In this paper, we review the principles, devices and schemes of cold atom experiments in ground and microgravity environment, the transfer between Zeeman states with different magnetic quantum numbers, magnetic phase transition, time-of-flight imaging and phase contrast imaging. As for the precise measurement, two aspects are emphasized: the deep cooling of atoms under microgravity and the use of non-destructive phase contrast imaging.
The optical system is a complex and precise subsystem for the atom interferometer (AI), especially for those used in field or space applications. Here, we introduce the design of the optical system of the China Space Station atom interferometer (CSSAI). The scheme is optimized to reduce the complexity while maintaining the capability to achieve dual-species AI. It features a fused silica optical bench with bonding technology, ensuring compactness and smaller thermal deformation. Spatial structures are designed to isolate the vibration and transfer the heat. After assembling, the optical system has a size of 250 mm × 240 mm × 104 mm and weighs 5.2 kg. After installing in the CSSAI, it passed the thermal and mechanical tests and then launched to the China Space Station (CSS). The output laser power changes are less than 15% from ground to space, and its long-term fluctuations are less than 2.5% for months in space. Cold atom preparation and interference are also realized in space. This optical system is extremely integrated and robust, which provides a foundation for the design of future cold atom payloads in space.