Quantum Dynamical Phase Transition in a Spin-Orbit Coupled Bose Condensate

Spin-orbit coupled bosons can exhibit rich equilibrium phases at low temperature and in the presence of particle-particle interactions. In the case with a 1D synthetic spin-orbit interaction, it has been observed that the ground state of a Bose gas can be a normal phase, stripe phase, or magnetized phase in different experimentally controllable parameter regimes. The magnetized states are doubly degenerate and consist of a many-particle two-state system. In this work, we investigate the nonequilibrium quantum dynamics by switching on an external perturbation to induce resonant couplings between the magnetized phases, and predict the novel quantum spin dynamics which cannot be obtained in the single-particle systems. In particular, due to particle-particle interactions, the transition of the Bose condensate from one magnetized phase to the other is forbidden when the strength of external perturbation is less than a critical value, and a full transition can occur only when the perturbation exceeds such critical strength. This phenomenon manifests itself a quantum dynamical phase transition, with the critical point behavior being exactly solvable. From the numerical simulations and exact analytic studies we show that the predicted many-body effects can be well observed with the current experiments.Comment: 9 pages, 4 figures, plus supplementary materia

A generic theory for Majorana zero modes in 2D superconductors

It is well known that non-Abelian Majorana zero modes (MZM) harbor at vortex cores in a $p_{x}+\text{i}p_{y}$ topological superconductor, which can be realized in a 2D spin-orbit coupled system with a single Fermi surface and by proximity coupling to an $s$-wave superconductor. Here we show that existence of non-Abelian MZMs is unrelated to the bulk topology of a 2D superconductor, and propose that such exotic modes can be resulted in much broader range of superconductors, being topological or trivial. For a generic 2D system with multiple Fermi surfaces and gapped out by superconducting pairings, we show that at least a single MZM survives if there are only odd number of Fermi surfaces of which the corresponding superconducting orders have vortices, and such MZM is protected by an emergent Chern-Simons invariant, irrespective of the bulk topology of the superconductor. This result may enrich new experimental schemes for realizing non-Aelian MZMs. In particular, we propose a minimal scheme to realize the MZMs in a 2D superconducting Dirac semimetal with trivial bulk topology, which can be well achieved based on the recent cold atom experiments.Comment: 5 pages, 3 figures, plus Supplementary Materia

Adsorption at Treated Steel-Paint Interfaces

In this thesis, a wide range of surface sensitive techniques have been used to characterise surfaces relevant to offshore steel structures, to provide fundamental understanding of steel-paint binding that prolongs coating lifespans and corrosion inhibition. Particular steel surfaces are characterised before and after almandine garnet abrasive blasting. Significant build-up and coverage of abrasive residue (almandine and calcium carbonate) is identified on the post-treatment steel, covering up to a third of the steel surface; Given the importance of the blasting materials on the surface, almandine garnet is also characterised for its surface chemistry and behaviour. By characterising both bare steel and almandine garnet, adsorption on `real' garnet-blasted steel substrates can be modelled. A dry ice-garnet mixed stream is also investigated to see whether abrasive residue could be reduced. It is found that a quarter of the steel surface is covered with blasting residue. However, cooling and moisture-condensation leads to corrosion spots formation. The adsorption of potential paint additives and components on S355 steel and garnet are determined using solution depletion isotherms. Quantitative data such as equilibrium adsorption constants, and estimation of monolayer molecular geometries are collected. The latter is further investigated through novel surface spectroscopy. In brief, most organics are found to have higher The steel surface is shown to be likely to corrode in offshore conditions with corrosion marine aerosols in a matter of a few hours. It is these corrosion products which will be substrates for coating/paint molecules. A `salt drop' corrosion study simulates relatively short timescale aerosol exposure (mins to hours). Surface chemical-environments are characterised. The corrosion products are found to be porous, inhomogeneous in chemical environment, and evolve through time, with adsorbed/occluded marine ions. Finally, as steel corrosion products are likely to adsorb marine salts, ion adsorption on almandine garnet is investigated. Cations of sodium, magnesium, and calcium are found to specifically adsorb. Numerical model co-fitting of data from different techniques successfully obtains the adsorption equilibria and constant, and the surface site density of almandine garnet. The study highlights a general need for more complete studies, using multiple adsorption experiments, for aqueous phase adsorption investigations on minerals in the future.Royal Dutch Shel

Swift2Android 利用源對源編譯器實現Swift 語言開發安卓軟件

At present, there are two main mobile platforms in the world, iOS and Android. These platforms have multitudinous resistances, so that no code can compile data from the two platforms simultaneously. Therefore, to satisfy their various clients, programmers have to set codes twice for the two distinct platforms... 目前全球普遍使用的流動平台主要分為iOS 和安卓兩種，兩個平台 之間互不兼容，以至無人能利用同一套編碼同時支援兩個平台。為 了滿足不同的客戶，編程人員必須撰寫兩套截然不同的編碼，而且 更要決定優先開發哪套編碼... Award: Gold奬項: 金

Exact new mobility edges between critical and localized states

The disorder systems host three types of fundamental quantum states, known as the extended, localized, and critical states, of which the critical states remain being much less explored. Here we propose a class of exactly solvable models which host a novel type of exact mobility edges (MEs) separating localized states from robust critical states, and propose experimental realization. Here the robustness refers to the stability against both single-particle perturbation and interactions in the few-body regime. The exactly solvable one-dimensional models are featured by quasiperiodic mosaic type of both hopping terms and on-site potentials. The analytic results enable us to unambiguously obtain the critical states which otherwise require arduous numerical verification including the careful finite size scalings. The critical states and new MEs are shown to be robust, illustrating a generic mechanism unveiled here that the critical states are protected by zeros of quasiperiodic hopping terms in the thermodynamic limit. Further, we propose a novel experimental scheme to realize the exactly solvable model and the new MEs in an incommensurate Rydberg Raman superarray. This work may pave a way to precisely explore the critical states and new ME physics with experimental feasibility.Comment: 5+6 pages, 4+5 figures. Discussions are updated. Under second round of revie

Corrosion inhibition of steel in seawater through surface phosphate formed from oil

Bis(2-ethylhexyl) phosphate (BEHP) was exposed to carbon steel surfaces from dry and water-saturated dodecane. The resulting changes to the surfaces were characterised using spectroscopic techniques (energy dispersive X-ray (EDX), X-ray photoelectron (XPS), and far-infrared reflection absorption (RAIRS) spectroscopies) and polarised neutron reflectometry (PNR). Although there was no observable affinity of BEHP to the steel surface in dry solvent, a layer of rough iron (III) phosphate formed in water-saturated dodecane. The phosphate-reacted steel surface showed some resistance to corrosion by seawater, suggesting the formation of a cohesive barrier against corrosive species. The results support the use of BEHP as an anti-corrosion additive and a viable phosphating agent for steel surfaces.Royal Dutch Shell Company; The Croucher Foundation, Hong Kon