title: Test of the Universality of Free Fall with Atoms in Different Spin Orientations.
abstract: We report a test of the universality of free fall by comparing the gravity acceleration of the ^{87}Rb atoms in m_{F}=+1 versus those in m_{F}=-1, of which the corresponding spin orientations are opposite. A Mach-Zehnder-type atom interferometer is exploited to alternately measure the free fall acceleration of the atoms in these two magnetic sublevels, and the resultant Eötvös ratio is η_{S}=(0.2±1.2)×10^{-7}. This also gives an upper limit of 5.4×10^{-6}  m^{-2} for a possible gradient field of the spacetime torsion. The interferometer using atoms in m_{F}=±1 is highly sensitive to the magnetic field inhomogeneity. A double differential measurement method is developed to alleviate the inhomogeneity influence, of which the effectiveness is validated by a magnetic field modulating experiment.
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Xiao-Chun
authors.initials: XC
authors.lastname: Duan
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Xiao-Bing
authors.initials: XB
authors.lastname: Deng
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Min-Kang
authors.initials: MK
authors.lastname: Zhou
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Ke
authors.initials: K
authors.lastname: Zhang
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Wen-Jie
authors.initials: WJ
authors.lastname: Xu
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Feng
authors.initials: F
authors.lastname: Xiong
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Yao-Yao
authors.initials: YY
authors.lastname: Xu
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Cheng-Gang
authors.initials: CG
authors.lastname: Shao
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.|Sun Yat-sen University, Guangzhou 510275, People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Luo
authors.affiliation: MOE Key Laboratory of Fundamental Physical Quantities Measurements, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Zhong-Kun
authors.initials: ZK
authors.lastname: Hu