In quenching a topological phase across phase transition, the dynamical bulk-surface correspondence emerges that the bulk topology of d-dimensional (dD) phase relates to the nontrivial pattern of quench dynamics emerging on (d − 1)D subspace, called band inversion surfaces (BISs) in momentum space. Here we report the first experimental observation of the dynamical bulk-surface correspondence through measuring the topological charges in a 2D quantum anomalous Hall model realized in an optical Raman lattice. The system can be quenched with respect to every spin axis by suddenly varying the two-photon detuning or phases of the Raman couplings, in which the topological charges and BISs are measured dynamically by the time-averaged spin textures. We observe that the total charges in the region enclosed by BISs define a dynamical topological invariant, which equals the Chern index of the post-quench band. The topological charges relate to an emergent dynamical field which exhibits nontrivial topology on BIS, rendering the dynamical bulk-surface correspondence. This study opens a new avenue to explore topological phases dynamically. arXiv:1905.06478v1 [cond-mat.quant-gas]

Ultra-low noise magnetic field is essential for many branches of scientific research. Examples include experiments conducted on ultra-cold atoms, quantum simulations, as well as precision measurements. In ultra-cold atom experiments specifically, a bias magnetic field will be often served as a quantization axis and be applied for Zeeman splitting. As atomic states are usually sensitive to magnetic fields, a magnetic field characterized by ultra-low noise as well as high stability is typically required for experimentation. For this study, a bias magnetic field is successfully stabilized at 14.5G, with the root mean square (RMS) value of the noise reduced to 18.5µG (1.28ppm) by placing µ-metal magnetic shields together with a dynamical feedback circuit. Long-time instability is also regulated consistently below 7µG. The level of noise exhibited in the bias magnetic field is further confirmed by evaluating the coherence time of a Bose-Einstein condensate characterized by Rabi oscillation. It is concluded that this approach can be applied to other physical systems as well.

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