Radio-frequency spectroscopy of a strongly interacting spin-orbit coupled Fermi gas

We investigate experimentally and theoretically radio-frequency spectroscopy and pairing of a spin-orbit-coupled Fermi gas of $^{40}$K atoms near a Feshbach resonance at $B_{0}=202.2$ G. Experimentally, the integrated spectroscopy is measured, showing characteristic blue and red shifts in the atomic and molecular responses, respectively, with increasing spin-orbit coupling. Theoretically, a smooth transition from atomic to molecular responses in the momentum-resolved spectroscopy is predicted, with a clear signature of anisotropic pairing at and below resonance. Our many-body prediction agrees qualitatively well with the observed spectroscopy near the Feshbach resonance.Comment: 7 pages, 4 figures. Supercedes 1302.055

Atomic Bose-Einstein condensate in a twisted-bilayer optical lattice

Observation of strong correlations and superconductivity in twisted-bilayer-graphene have stimulated tremendous interest in fundamental and applied physics. In this system, the superposition of two twisted honeycomb lattices, generating a Moir$\acute{\mathrm{e}}$ pattern, is the key to the observed flat electronic bands, slow electron velocity and large density of states. Despite these observations, a full understanding of the emerging superconductivity from the coupled insulating layers and the appearance of a small magic angle remain a hot topic of research. Here, we demonstrate a quantum simulation platform to study superfluids in twisted bilayer lattices based on Bose-Einstein condensates loaded into spin-dependent optical lattices. The lattices are made of two sets of laser beams that independently address atoms in different spin states, which form the synthetic dimension of the two layers. The twisted angle of the two lattices is controlled by the relative angle of the laser beams. We show that atoms in each spin state only feel one set of the lattice and the interlayer coupling can be controlled by microwave coupling between the spin states. Our system allows for flexible control of both the inter- and intralayer couplings. Furthermore we directly observe the spatial Moir$\acute{\mathrm{e}}$ pattern and the momentum diffraction, which confirm the presence of atomic superfluid in the bilayer lattices. Our system constitutes a powerful platform to investigate the physics underlying the superconductivity in twisted-bilayer-graphene and to explore other novel quantum phenomena difficult to realize in materials.Comment: 6 pages, 5 figure

Research on the Green Effect of Environmental Policies—From the Perspective of Policy Mix

Environmental protection policy serves as an effective means for the government to curb environmental pollution and promote high-quality economic development. The government must weigh the effects of different policy mixes. From the perspective of policy combination, this paper discusses the green effect of environmental protection policy theoretically and empirically. First and foremost, this paper sorts out the reforming time of environmental protection taxes and the situation of the low-carbon pilot city, and puts forward two hypotheses. Furthermore, by referring to the environmental protection tax, the policy for the low-carbon pilot city, and the urban air quality indicator from 2014 to 2020, this paper explores the green effect of the environmental protection policy and further validates the consolidation effect of the policy mix on the green effect. The study reveals a significant decrease in the air pollution level in regions with higher standards for levying an environmental protection tax. The conclusion remains robust via parallel trend testing and substitution of the subject variables. Furthermore, an analysis of the policy mix of an environmental protection tax indicates that the policy mix of an environmental protection tax and low-carbon city produces a significant green effect, which not only curbs air pollution but also reduces greenhouse gas emissions. An in-depth analysis shows that an environmental protection tax has the best green effect in the first and second areas of a low-carbon pilot market. The synergies of low-carbon pilot effects are higher in areas with low and middle tax rates