# Browsing by Author "Luo, Xi-Wang"

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Item Adiabatically Tuning Quantized Supercurrents in an Annular Bose-Einstein Condensate(2018-08-20) Hou, Junpeng; Luo, Xi-Wang; Sun, Kuei; Zhang, Chuanwei; Hou, Junpeng; Luo, Xi-Wang; Sun, Kuei; Zhang, ChuanweiShow more The ability to generate and tune quantized persistent supercurrents is crucial for building superconducting or atomtronic devices with novel functionalities. In ultracold atoms, previous methods for generating quantized supercurrents are generally based on dynamical processes to prepare atoms in metastable excited states. Here, we show that arbitrary quantized circulation states can be adiabatically prepared and tuned as the ground state of a ring-shaped Bose-Einstein condensate by utilizing spin-orbital-angular-momentum (SOAM) coupling and an external potential. There exists superfluid hysteresis for tuning supercurrents between different quantization values with nonlinear atomic interactions, which is explained by developing a nonlinear Landau-Zener theory. Our work will provide a powerful platform for studying SOAM-coupled ultracold atomic gases and building atomtronic circuits.Show more Item Momentum Space Aharonov-Bohm Interferometry in Rashba Spin-Orbit Coupled Bose-Einstein Condensates(Institute of Physics Publishing) Hou, Junpeng; Luo, Xi-Wang; Sun, Kuei; Zhang, Chuanwei; 4042455 (Zhang, C); Hou, Junpeng; Luo, Xi-Wang; Sun, Kuei; Zhang, ChuanweiShow more The recent experimental realization of synthetic Rashba spin-orbit coupling (SOC) paves a new avenue for exploring topological phases in ultracold atoms. The unequivocal characterization of such topological physics requires a simple scheme for measuring the Berry phase originating from the SOC. Here we propose a scheme to realize momentum space Aharonov-Bohm interferometry in a Rashba spin-orbit-coupled Bose-Einstein condensate through a sudden change of the in-plane Zeeman field. We find that the π Berry phase for the Dirac point of the Rashba SOC is directly revealed by a robust dark interference fringe in the momentum space. An external perpendicular Zeeman field opens a band gap at the Dirac point, which reduces the Berry phase along the Rashba ring, leading to lower brightness of the interference fringe. We develop a variational model with semiclassical equations of motion of essential dynamical quantities for describing the interference process, yielding real and momentum space trajectories and geometric phases agreeing with the real-time simulation of the Gross-Pitaevskii equation. Our study may pave the way for the experimental detection of Berry phases in ultracold atomic systems and further exploration of momentum space interference dynamics.Show more Item Momentum-Space Josephson Effects(Amer Physical Soc) Hou, Junpeng; Luo, Xi-Wang; Sun, Kuei; Bersano, Thomas; Gokhroo, Vandna; Mossman, Sean; Engels, Peter; Zhang, Chuanwei; 0000 0000 3722 2361 (Zhang, C); 4042455 (Zhang, C); Hou, Junpeng; Luo, Xi-Wang; Sun, Kuei; Zhang, ChuanweiShow more The Josephson effect is a prominent phenomenon of quantum supercurrents that has been widely studied in superconductors and superfluids. Typical Josephson junctions consist of two real-space superconductors (superfluids) coupled through a weak tunneling barrier. Here we propose a momentum-space Josephson junction in a spin-orbit coupled Bose-Einstein condensate, where states with two different momenta are coupled through Raman-assisted tunneling. We show that Josephson currents can be induced not only by applying the equivalent of "voltages," but also by tuning tunneling phases. Such tunneling-phase-driven Josephson junctions in momentum space are characterized through both full mean field analysis and a concise two-level model, demonstrating the important role of interactions between atoms. Our scheme provides a platform for experimentally realizing momentum-space Josephson junctions and exploring their applications in quantum-mechanical circuits.Show more Item Self-Adapted Floquet Dynamics of Ultracold Bosons in a Cavity(American Physical Society) Luo, Xi-Wang; Zhang, Chuanwei; Luo, Xi-Wang; Zhang, ChuanweiShow more Floquet dynamics of a quantum system subject to periodic modulations of system parameters provides a powerful tool for engineering new quantum matter with exotic properties. While system dynamics is significantly altered, the periodic modulation itself is usually induced externally and independent of Floquet dynamics. Here we propose a new type of Floquet physics for a Bose-Einstein condensate (BEC) subject to a shaken lattice generated inside a cavity, where the shaken lattice and atomic Floquet bands are mutually dependent, resulting in self-adapted Floquet dynamics. In particular, the shaken lattice induces Floquet quasienergy bands for the BEC, whose backaction leads to a self-adapted dynamical normal-superradiant phase transition for the shaken lattice. Such self-adapted Floquet dynamics shows two surprising and unique features: (i) The normal-superradiant phase transition possesses a hysteresis even without atom interactions. (ii) The dynamical atom-cavity steady state could exist at free energy maxima. The atom interactions strongly affect the phase transition of the BEC from zero to finite momenta. Our results provide a powerful platform for exploring self-adapted Floquet physics, which may open an avenue for engineering novel quantum materials. © 2018 American Physical Society.Show more Item Spin-Tensor-Momentum-Coupled Bose-Einstein Condensates(American Physical Society, 2017-11-06) Luo, Xi-Wang; Sun, Kuei; Zhang, Chuanwei; Luo, Xi-Wang; Sun, Kuei; Zhang, ChuanweiShow more The recent experimental realization of spin-orbit coupling for ultracold atomic gases provides a powerful platform for exploring many interesting quantum phenomena. In these studies, spin represents the spin vector (spin 1/2 or spin 1) and orbit represents the linear momentum. Here we propose a scheme to realize a new type of spin-tensor-momentum coupling (STMC) in spin-1 ultracold atomic gases. We study the ground state properties of interacting Bose-Einstein condensates with STMC and find interesting new types of stripe superfluid phases and multicritical points for phase transitions. Furthermore, STMC makes it possible to study quantum states with dynamical stripe orders that display density modulation with a long tunable period and high visibility, paving the way for the direct experimental observation of a new dynamical supersolidlike state. Our scheme for generating STMC can be generalized to other systems and may open the door for exploring novel quantum physics and device applications.Show more