We employ the hysteretic behavior of a superconducting thin film in the remanent state to generate different traps and flexible magnetic potentials for ultra-cold atoms. The trap geometry can be programmed by externally applied fields. This new approach for atom-optics is demonstrated by three different trap types realized on a single micro-structure: a Z-type trap, a double trap and a bias field free trap. Our studies show that superconductors in the remanent state provide a new versatile platform for atom-optics and applications in ultra-cold quantum gases.PACS numbers: 37.10.Gh, 03.75.Be, 74.78.NaThe use of superconductors in atom chips [1-3] is a recent development, presenting new opportunities for atom optics [4][5][6][7][8]. One demonstrated advantage of superconductors over conventional conductors is the significant reduction of near-field noise in current-carrying structures leading to low atomic heating rates and enhanced spin-flip lifetimes [9][10][11][12][13][14]. Proposals in this area advocate experimental designs for coherent coupling with atomic or molecular quantum systems that exploit the distinct properties of superconductors [15][16][17][18][19][20][21][22].In a previous paper we have demonstrated that the remanent magnetization created by vortices can be used to trap ultra cold atoms without applying a transport current [23]. Other groups have created quadrupole type traps [24] and have shown that vortices modify the trapping potential created by a transport current in a Z-type trap [25]. In this article, we show that the unique response of superconductors to applied magnetic field enables programmable magnetic trap geometries for ultra cold atoms. We demonstrate this new approach by generating three different atom trap geometries on a fixed superconducting micro-structure. We can choose the geometry by applying a suitable external magnetic field sequence. The trapping potentials are generated by spatial magnetic patterns imprinted on a thin film, using the hysteretic response of type-II superconductors.The three different geometries we realize in this article to demonstrate this new approach are shown schematically in Fig.
High atomic diffusivity in metals enables substantial tuneability of their structure and properties by tailoring the diffusional processes, but this causes their customized properties to be unstable at elevated temperatures. Eliminating diffusive interfaces by fabricating single crystals or heavily alloying helps to address this issue but does not inhibit atomic diffusion at high homologous temperatures. We discovered that the Schwarz crystal structure was effective at suppressing atomic diffusion in a supersaturated aluminum–magnesium alloy with extremely fine grains. By forming these stable structures, diffusion-controlled intermetallic precipitation from the nanosized grains and their coarsening were inhibited up to the equilibrium melting temperature, around which the apparent across-boundary diffusivity was reduced by about seven orders of magnitude. Developing advanced engineering alloys using the Schwarz crystal structure may lead to useful properties for high-temperature applications.
The galvanic corrosion behavior between pure Al and synthesized bulk Mg 2 Si in 0.01 M NaCl solution at different pH values has been investigated by the scanning vibrating electrode technique (SVET). At pH 2, bulk Mg 2 Si actively dissolves and it acts as an anode. With the increase of exposure time, the anodic activity of Mg 2 Si decreases drastically and eventually anodic activity appears on Al surface. In alkaline solution, Mg 2 Si phase always acts as the cathode. The preferential dissolution of Mg and enrichment of Si found by energy dispersive X-ray spectroscopy are responsible for the observed anodic activity decay of Mg 2 Si in acidic solution. At pH 6, the galvanic corrosion current of Al/Mg 2 Si couple is much less than those at pH 2 and pH 13, and Mg 2 Si mainly undergoes self-dissolution. These results indicate that the dealloying of binary Mg 2 Si phase depends on the solution pH value and corrosion time, which subsequently have a great influence on the galvanic corrosion current of Al/Mg 2 Si couple. Al-Mg-Si alloys are widely used in automotive, aerospace and rail transportation industries because of their high stiffness, good formability, good weldability and high corrosion resistance.1-5 Due to the low solubility of the alloying additions, second phases (such as Mg 2 Si precipitates) are commonly formed in Al-Mg-Si alloys.6 These particles have different electrochemical activities from the alloy matrix, thus galvanic corrosion can occur between the particles and surrounding matrix, 7-10 which gives rise to the degradation of Al alloys in industrial applications.Potentiodynamic polarization tests carried out by Buchheit et al. 7,8 have shown that the corrosion potential of Mg 2 Si is much lower than the alloy matrix. The Volta potential of Mg 2 Si particle measured by scanning kelvin probe force microscopy (SKPFM) is about 100∼180 mV lower than the aluminum matrix. 10 These reports indicate that Mg 2 Si particle is initially anodic relative to the aluminum matrix.Selective dissolution of Mg has been found by many research groups during the corrosion of Mg 2 Si phases. 4,9,[11][12][13] For example, Jain et al. 11 found that Mg 2 Si particle can selectively dissolve in neutral solution. Wolka et al.12 measured the open circuit potential (OCP) of Mg 2 Si using a microcapillary electrochemical cell and stated that the increase of OCP after 1 h immersion in 0.01 M NaCl solution is due to the preferential dissolution of Mg. Mg 2 Si particles in AlMg-Si alloys have also been investigated by SKPFM in combination with atomic force microscopy (AFM) observation, 13 electrochemical micro-cell measurements combined with electron probe micro analysis (EPMA) and auger electron spectroscopy (AES).4 These techniques reveal that high reactivity of Mg leads to the dealloying of Mg 2 Si particles accompanied with the enrichment of Si, which finally makes the Mg 2 Si remnant exhibit cathodic activity. Although SKPFM can measure Volta potential, it cannot provide kinetics parameters relating to the galvanic corrosion ...
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