Quantum phases of the biased two-chain-coupled Bose-Hubbard Ladder

We investigate the quantum phases of bosons in a two-chain-coupled ladder. This bosonic ladder is generally in a biased configuration, meaning that the two chains of the ladder can have dramatically different on-site interactions and potential energies. Adopting the numerical density-matrix renormalization-group method, we analyze the phase transitions in various parameter spaces. We find signatures of both insulating-to-superfluid and superfluid-to-insulating quantum phase transitions as the interchain tunnelling is increased. Interestingly, tunning the interaction to some intermediate values, the system can exhibit a reentrant quantum phase transition between insulating and superfluid phases. We show that for infinite interaction bias, the model is amenable to some analytical treatments, whose prediction about the phase boundary is in great agreement with the numerical results. We finally clarify some critical parameters which separate the system into regimes with distinct phase behaviours, and briefly compare typical properties of the biased and unbiased bosonic ladder systems. Our work enriches the Bose-Hubbard physics.Comment: 10 pages, 7 figure

Spin-tensor Meissner currents of ultracold bosonic gas in an optical lattice

We investigate the Meissner currents of interacting bosons subjected to a staggered artificial gauge field in a three-leg ribbon geometry, realized by spin-tensor--momentum coupled spin-1 atoms in a 1D optical lattice. By calculating the current distributions using the state-of-the-art density-matrix renormalization-group method, we find a rich phase diagram containing interesting Meissner and vortex phases, where the currents are mirror symmetric with respect to the {\color{red}middle leg} (i.e., they flow in the same direction on the two boundary legs opposite to that on the middle leg), leading to the spin-tensor type Meissner currents, which is very different from previously observed chiral edge currents under uniform gauge field. The currents are uniform along each leg in the Meissner phase and form vortex-antivortex pairs in the vortex phase. Besides, the system also support a polarized phase that spontaneously breaks the mirror symmetry, whose ground states are degenerate with currents either uniform or forming vortex-antivortex pairs. We also discuss the experimental schemes for probing these phases. Our work provides useful guidance to ongoing experimental research on synthetic flux ribbons and paves the way for exploring novel many-body phenomena therein.Comment: 10 pages, 9 figure

Exploring interacting topological insulator of extended Su-Schrieffer-Heeger model

Exploring topological phases in interacting systems is a challenging task. We investigate many-body topological physics of interacting fermions in an extended Su-Schrieffer-Heeger (SSH) model, which extends the two sublattices of SSH model into four sublattices and thus is dubbed SSH4 model, based on the density-matrix renormalization-group numerical method. The interaction-driven phase transition from topological insulator to charge density wave (CDW) phase can be identified by analyzing the variations of entanglement spectrum, entanglement entropies, energy gaps, CDW order parameter, and fidelity. We map the global phase diagram of the many-body ground state, which contains nontrivial topological insulator, trivial insulator and CDW phases, respectively. In contrast to interacting SSH model, in which the phase transitions to the CDW phase are argued to be first-order phase transitions, the phase transitions between the CDW phase and topologically trivial/nontrivial phases are shown to be continuous phase transitions. Finally, we {also} show the phase diagram of interacting spinful SSH4 model, where the attractive (repulsive) on-site spin interaction amplifies (suppresses) the CDW phase. The models analyzed here can be implemented with ultracold atoms on optical superlattices.Comment: 9 pages, 5 figure

Energy harvesting, desalination and coastal protection by sscillating surge wave energy converter

As recognized by the United Nations, Food, Energy and Water (FEW) nexus is central to sustainable development, and the demand for all these three is increasing due to a rising global population, rapid urbanization, changing diets and economic growth. For the US, over 53% of the population lives within 50 miles of the coast (NOAA), the coastal zone is an interaction region between land and ocean and an interface of geosphere, hydrosphere, atmosphere, and biosphere, as well as greatly affected by human activities, the stability of coastal ecosystem is very weak. Oscillating surge wave energy converter can harvest energy from ocean waves to power saline water desalination and reduce the coastal erosion as physical barrier, and the desalinated fresh water can be used for saline-sodic-alkaline soil reclamation and make it suitable for plant growth and then act as a biological barrier. Power takeoff (PTO) is possibly the single most important element in wave energy technology, and underlines many (possibly most) of the failures to date (Falcão). The reason is that the wave energy is concentrated at low frequencies and oscillating velocities, which makes efficient conversion extremely difficult and limits the options for efficient power takeoff. A novel PTO, called mechanical motion rectifier (MMR), is proposed to convert bidirectional motion into unidirectional motion. Tank tests for small-scale prototypes have been down. Please click Additional Files below to see the full abstract