We report the experimental observation of tunable, non-reciprocal quantum transport of a Bose-Einstein condensate in a momentum lattice. By implementing a dissipative Aharonov-Bohm (AB) ring in momentum space and sending atoms through it, we demonstrate a directional atom flow by measuring the momentum distribution of the condensate at different times. While the dissipative AB ring is characterized by the synthetic magnetic flux through the ring and the laser-induced loss on it, both the propagation direction and transport rate of the atom flow sensitively depend on these highly tunable parameters. We demonstrate that the non-reciprocity originates from the interplay of the synthetic magnetic flux and the laser-induced loss, which simultaneously breaks the inversion and the time-reversal symmetries. Our results open up the avenue for investigating non-reciprocal dynamics in cold atoms, and highlight the dissipative AB ring as a flexible building element for applications in quantum simulation and quantum information. arXiv:2001.01859v1 [cond-mat.quant-gas]

We report the experimental implementation of discrete-time topological quantum walks of a Bose-Einstein condensate in momentum space. Introducing stroboscopic driving sequences to the generation of a momentum lattice, we show that the dynamics of atoms along the momentum lattice is dictated by a periodically driven Su-Schieffer-Heeger model, which is equivalent to a discretetime topological quantum walk. We directly measure the underlying topological invariants through time-averaged mean chiral displacements in different time frames, which are consistent with our experimental observation of topological phase transitions. The high tunability of the system further enables us to observe robust helical Floquet channels in the one-dimensional momentum lattice, which derive from the winding of Floquet quasienergy bands. Our experiment opens up the avenue of investigating discrete-time topological quantum walks using cold atoms, where the many-body environment and tunable interactions offer exciting new possibilities.Exploring topological phases is a main theme in modern physics. Characterized by topological invariants which reflect the global geometric properties of the system wave function, topological phases host a range of fascinating features, which are robust to local perturbations and are potentially useful for applications in quantum information and quantum computation [1,2]. Besides conventional topological materials in solid-state systems, topological phenomena also emerge away from equilibrium. For example, topological phases and emergent topological phenomena exist in non-Hermitian open systems [3][4][5][6][7][8][9][10][11][12][13][14], in periodically driven Floquet systems and quench processes [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], which have stimulated intense interest recently due to the rapid progress in synthetic quantum-simulation platforms such as cold atoms [34][35][36][37], photonics [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52], phononics [53], and superconducting qubits [54].A particularly interesting subject is topologies in periodically driven Floquet systems, which are shown to have a rich structure and host novel topological phases with no counterparts in static systems [20][21][22][23]. A paradigmatic example of topological Floquet dynamics is discrete-time quantum walks, which, besides potential applications in quantum information [55][56][57], have been widely used in photonics for the exploration of Floquet topological phases [38][39][40][41][42][43][44][45][46][47]. In cold atoms, whereas Floquet topological phases [34] and quantum walks [58] have been respectively implemented, quantum walks with topological properties are yet to be experimentally realized.Here we report the experimental implementation of discrete-time topological quantum walks in momentum space for a Bose-Einstein condensate (BEC). Combining the generation of momentum lattice [59-63] with stroboscopic driving sequences, dynamics of the conden-sate atoms is governed b...

Introduced oxygen vacancy on WO with specific exposed facets was prepared through facile solvothermal treatment and different cooling methods. We demonstrated that the density of oxygen defects could be regulated by different cooling methods and speculated that oxygen vacancy with appropriate concentration range could promote photocatalytic activity through suppressing the recombination of photo-induced carriers. The specific exposed facets with higher oxidation efficiency were prepared by solvothermal reaction. WO-A treated by air cooling exhibits the best photocatalytic oxygen evolution rate at 500 μmol g h using AgNO as sacrifice agent under visible light (λ > 400 nm) without any co-catalysts, which is about 2 times higher than WO-N without oxygen defects. This strategy, using different cooling methods to regulate oxygen vacancy concentration on tungsten oxides, could contribute to the design of other high efficiency photocatalysts.

With the improved understanding of the molecular pathogenesis and characteristics of cancers, the critical role of the immune system in preventing tumor development has been widely accepted. The understanding of the relationship between the immune system and cancer progression is constantly evolving, from the cancer immunosurveillance hypothesis to immunoediting theory and the delicate balance in the tumor microenvironment. Currently, immunotherapy is regarded as a promising strategy against cancers. Although adoptive cell therapy (ACT) has shown some exciting results regarding the rejection of tumors, the effect is not always satisfactory. Cellular therapy with CD4 + T cells remains to be further explored since the current ACT is mainly focused on CD8 + cytotoxic T lymphocytes (CTLs). Recently, Th9 cells, a subgroup of CD4 + T helper cells characterized by the secretion of IL-9 and IL-10, have been reported to be effective in the elimination of solid tumors and to exhibit superior antitumor properties to Th1 and Th17 cells. In this review, we summarize the most recent advances in the understanding of Th9 cell differentiation and the dual role, both anti-tumor and pro-tumor effects, of Th9 cells in tumor progression.

The electrochemical behavior of poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFDMS-b-PDMS) films deposited on a glassy carbon electrode was investigated by means of cyclic voltammetry (CV). The influences of the solvent, film thickness, temperature, and PDMS block length in PFDMS-b-PDMS on the electrode process were discussed. It was found that in 0.1 M aqueous LiClO(4) the electrochemical processes of the films on a glassy carbon electrode were complex and have a low rate of electron transport and mass diffusion. The kinetic parameters obtained indicated that the electrode process was controlled by both the electrode reaction and mass diffusion.

For laser cooling considerations, we have theoretically investigated the electronic, rovibrational and hyperfine structures of BaF molecule. The highly diagonal Franck-Condon factors and the branching ratios for all possible transitions within the lowest-lying four electronic states have also been calculated. Meanwhile, the mixing between metastable A 2 ∆ and A 2 Π states and further the lifetime of the ∆ state have been estimated since the loss procedure via ∆ state would like fatally destroy the main quasi-cycling Σ − Π transition for cooling and trapping. The resultant hyperfine splittings of each rovibrational states in X 2 Σ + state provide benchmarks for sideband modulations of cooling and repumping lasers and remixing microwaves to address all necessary levels. The calculated Zeeman shift and g-factors for both X and A states serve as benchmarks for selections of the trapping laser polarizations. Our study paves the way for future laser cooling and magneto-optical trapping of the BaF molecule.

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