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. 

Momentum filtering scheme of cooling atomic clouds for the Chinese Space Station

The Efimov effect and its universal property are of paramount importance in quantum few-body physics. Despite this, the predicted ground state Efimov resonance has not yet been observed in 39,40,41K-87Rb mixtures within the currently available observation window. Cooling atoms in the microgravity environment of outer space might overcome this limitation, whereas the residual curvature of the strong magnetic fields may result in significant atom leakage. In this work, we propose an optical method based on far-detuned time-averaged dipole potential to counteract the three-dimensional inhomogeneous field. The target intensity distribution can be conveniently obtained by modulating the central position of the quasi-1D print beam using acoustic optical modulators. Within a volume of 300 × 300 × 400 µm3, the residual potential fluctuations can be reduced by two orders of magnitude to less than 100 pK. The proposed approach offers a realistic prospect of investigating the Efimov-type resonance in the 40K-87Rb Bose-Fermi mixture.

Compensating three-dimensional field inhomogeneity in cold atom Efimov-state search by a time-averaged optical potential.

Efficient cold atom source from a single-layer atom chip

The capability to reach ultracold atomic temperatures in compact instruments has recently been extended into space. Ultracold temperatures amplify quantum effects, while free-fall allows further cooling and longer interactions time with gravity - the final force without a quantum description. On Earth, these devices have produced macroscopic quantum phenomena such as Bose-Einstein condensation (BECs), superfluidity, and strongly interacting quantum gases. Quantum sensors interfering the superposition of two ultracold atomic isotopes have tested the Universality of Free Fall (UFF), a core tenet of Einstein's classical gravitational theory, at the $10^{-12}$ level. In space, cooling the elements needed to explore the rich physics of strong interactions and preparing the multiple species required for quantum tests of the UFF has remained elusive. Here, utilizing upgraded capabilities of the multi-user Cold Atom Lab (CAL) instrument within the International Space Station (ISS), we report the first simultaneous production of a dual species Bose-Einstein condensate in space (formed from $^{87}$Rb and $^{41}$K), observation of interspecies interactions, as well as the production of $^{39}$K ultracold gases. We have further achieved the first space-borne demonstration of simultaneous atom interferometry with two atomic species ($^{87}$Rb and $^{41}$K). These results are an important step towards quantum tests of UFF in space, and will allow scientists to investigate aspects of few-body physics, quantum chemistry, and fundamental physics in novel regimes without the perturbing asymmetry of gravity.

pdf/quantum-gas-mixtures-and-dual-species-atom-interferometry-in-2jarx9sv.pdf

Quantum Gas Mixtures and Dual-Species Atom Interferometry in Space

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.

Deep cooling scheme of quantum degenerate gas and ground experimental verification for chinese space station

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 780 nm laser system and a low phase noise 1064 nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a 87Rb quantum degenerate gas with 1.2 × 105 atoms and a temperature below 30 nK 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.

https://ieeexplore.ieee.org/ielx7/4563994/4814557/10098699.pdf

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

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Deep cooling scheme of quantum degenerate gas and ground experimental verification for chinese space station

Momentum filtering scheme of cooling atomic clouds for the Chinese Space Station

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