Manipulation of quantum noise for precision measurements with cold atoms

Xiangyu Dong, Shengjie Jin, Hongmian Shui +2 more

Ultra-cold atoms provide ideal platforms for interferometry. The macroscopic matter-wave property of ultra-cold atoms leads to large coherent length and long coherent time, which enable high accuracy and sensitivity to measurement. Here, we review our efforts to improve the performance of the interferometer. We demonstrate a shortcut method for manipulating ultra-cold atoms in an optical lattice. Compared with traditional ones, this shortcut method can reduce the manipulation time by up to three orders of magnitude. We construct a matter-wave Ramsey interferometer for trapped motional quantum states and significantly increase its coherence time by one order of magnitude with an echo technique based on this method. Efforts have also been made to enhance the resolution by multimode scheme. Application of a noise-resilient multi-component interferometer shows that increasing the number of paths could sharpen the peaks in the time-domain interference fringes, which leads to a resolution nearly twice compared with that of a conventional double-path two-mode interferometer. With the shortcut method mentioned above, improvement of the momentum resolution could also be fulfilled, which leads to atomic momentum patterns less than 0.6 ℏkL . To identify and remove systematic noises, we introduce the methods based on the principal component analysis (PCA) that reduce the noise in detection close to the 1 / 2 of the photon-shot noise and separate and identify or even eliminate noises. Furthermore, we give a proposal to measure precisely the local gravity acceleration within a few centimeters based on our study of ultracold atoms in precision measurements.

Wen-Cui Peng, Biao Tang, Wei Jian Yang +3 more

T. Takano, Shin-Ichi-Ro Tanaka, Ryo Namiki +1 more

We report successful manipulation of nonclassical atomic spin states. We apply an off-resonant noncircularly-polarized light pulse to a measurement-induced squeezed spin state of a cold atomic ensemble. By changing the pulse duration, we clearly observe a rotation of the anisotropic quantum-noise distribution in good contrast with the case of manipulation of a coherent spin state where the quantum-noise distribution is always isotropic. This is an important step for quantum state tomography, quantum swapping, and precision spectroscopic measurement.

Roy S. Bondurant

Wei Wang, Hao Zhu, Li Wang +3 more

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.