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1.  A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS 
Journal of Applied Crystallography  2013;46(Pt 4):874-881.
Three-dimensional reciprocal space mapping by X-ray and electron diffraction [namely grazing-incidence X-ray diffraction (GIXD), reflection high-energy electron diffraction (RHEED) and grazing-incidence small-angle X-ray scattering (GISAXS)] was used to explore the internal structure and shape of differently oriented epitaxial Co/CaF2 facetted nanoparticles.
In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.
doi:10.1107/S0021889813008777
PMCID: PMC3769055  PMID: 24046491
cobalt-on-fluorite nanoparticles; grazing-incidence X-ray diffraction (GIXD); reflection high-energy electron diffraction (RHEED); grazing-incidence small-angle X-ray scattering (GISAXS); epitaxial growth; three-dimensional reciprocal space mapping
2.  Depth profiling of polymer films with grazing-incidence small-angle X-ray scattering 
A procedure for obtaining depth-specific scattering profiles of laterally defined nanostructure using grazing-incidence small-angle X-ray scattering is described.
A model-free method of reconstructing depth-specific lateral scattering from incident-angle-resolved grazing-incidence small-angle X-ray scattering (GISAXS) data is proposed. The information on the material which is available through variation of the X-ray penetration depth with incident angle is accessed through reference to the reflected branch of the GISAXS process. Reconstruction of the scattering from lateral density fluctuations is achieved by solving the resulting Fredholm integral equation with minimal a priori information about the experimental system. Results from simulated data generated for hypothetical multilayer polymer systems with constant absorption coefficient are used to verify that the method can be applied to cases with large X-ray penetration depths, as typically seen with polymer materials. Experimental tests on a spin-coated thick film of a blend of diblock copolymers demonstrate that the approach is capable of reconstruction of the scattering from a multilayer structure with the identification of lateral scattering profiles as a function of sample depth.
doi:10.1107/S0108767309007508
PMCID: PMC2724987  PMID: 19349663
depth profiling; grazing-incidence small-angle X-ray scattering; block copolymers
3.  Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots 
A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model.
doi:10.1007/s11671-010-9786-8
PMCID: PMC3212094
Molecular beam epitaxy; Self-assembled quantum dots; Inter-dot coupling; Anisotropic effects; Linear polarized photoluminescence emission; Grazing-incidence X-ray diffraction synchrotron; Optoelectronic
4.  New approach for structural characterization of planar sets of nanoparticles embedded into a solid matrix 
Scientific Reports  2013;3:3414.
In this work we demonstrate that Medium Energy Ion Scattering (MEIS) measurements in combination with Transmission Electron Microscopy (TEM) or Grazing Incidence Small Angle X-Ray Scattering (GISAXS) can provide a complete characterization of nanoparticle (NP) systems embedded into dielectric films. This includes the determination of the nanoparticle characteristics (location, size distribution and number concentration) as well as the depth distribution and concentration of the NP atomic components dispersed in the matrix. Our studies are performed considering a model case system consisting of planar arrangements of Au NPs (size range from 1 to 10 nm) containing three distinct Au concentrations embedded in a SiO2 film.
doi:10.1038/srep03414
PMCID: PMC3849636  PMID: 24301257
5.  Quantum-dot supercrystals for future nanophotonics 
Scientific Reports  2013;3:1727.
The study of supercrystals made of periodically arranged semiconductor quantum dots is essential for the advancement of emerging nanophotonics technologies. By combining the strong spatial confinement of elementary excitations inside quantum dots and exceptional design flexibility, quantum-dot supercrystals provide broad opportunities for engineering desired optical responses and developing superior light manipulation techniques on the nanoscale. Here we suggest tailoring the energy spectrum and wave functions of the supercrystals' collective excitations through the variation of different structural and material parameters. In particular, by calculating the excitonic spectra of quantum dots assembled in two-dimensional Bravais lattices we demonstrate a wide variety of spectrum transformation scenarios upon alterations in the quantum dot arrangement. This feature offers unprecedented control over the supercrystal's electromagnetic properties and enables the development of new nanophotonics materials and devices.
doi:10.1038/srep01727
PMCID: PMC3635059
6.  Properties and applications of quantum dot heterostructures grown by molecular beam epitaxy 
Nanoscale Research Letters  2006;1(1):32-45.
One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two: quantum wires and quantum dots, in order to realize novel devices that make use of low-dimensional confinement effects. One of the promising fabrication methods is to use self-organized three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. This article is intended to convey the flavour of the subject by focussing on the structural, optical and electronic properties and device applications of self-assembled quantum dots and to give an elementary introduction to some of the essential characteristics.
doi:10.1007/s11671-006-9017-5
PMCID: PMC3246631
Heterostructures; Semiconductors; Self-assembly; Quantum dots; Lasers; Optoelectronics
7.  Structural rearrangements in a lamellar diblock copolymer thin film during treatment with saturated solvent vapor 
Macromolecules  2010;43(1):418-427.
We have investigated the structural changes in thin films of lamellar poly(styrene-b-butadiene) diblock copolymers during treatment with saturated cyclohexane vapor, a solvent slightly selective for polybutadiene. Using real-time, in-situ grazing-incidence small-angle X-ray scattering (GISAXS), the swelling and the rearrangement of the lamellae were investigated with a time resolution of a few seconds, and the underlying processes on the molecular level were identified. After a few minutes in vapor, a transient state with a more well-defined and more long-range ordered lamellar orientation was encountered. Additional parallel lamellae formed which we attribute to the increased degree of coiling of the polymers in the swollen state. Eventually, the film became disordered. These changes are attributed to the increased mobility of the swollen polymers and the gradually decreasing segment-segment interaction parameter in the film as solvent is absorbed.
doi:10.1021/ma9017795
PMCID: PMC2841441  PMID: 20305742
polymer physics; diblock copolymers; thin films; grazing-incidence small-angle X-ray scattering
8.  Low-temperature fabrication of layered self-organized Ge clusters by RF-sputtering 
Nanoscale Research Letters  2011;6(1):341.
In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.
doi:10.1186/1556-276X-6-341
PMCID: PMC3211430  PMID: 21711858
9.  Self-Assembling Complexes of Quantum Dots and scFv Antibodies for Cancer Cell Targeting and Imaging 
PLoS ONE  2012;7(10):e48248.
Semiconductor quantum dots represent a novel class of fluorophores with unique physical and chemical properties which could enable a remarkable broadening of the current applications of fluorescent imaging and optical diagnostics. Complexes of quantum dots and antibodies are promising visualising agents for fluorescent detection of selective biomarkers overexpressed in tumor tissues. Here we describe the construction of self-assembling fluorescent complexes of quantum dots and anti-HER1 or anti-HER2/neu scFv antibodies and their interactions with cultured tumor cells. A binding strategy based on a very specific non-covalent interaction between two proteins, barnase and barstar, was used to connect quantum dots and the targeting antibodies. Such a strategy allows combining the targeting and visualization functions simply by varying the corresponding modules of the fluorescent complex.
doi:10.1371/journal.pone.0048248
PMCID: PMC3484990  PMID: 23133578
10.  Reversible Morphology Control in Block Copolymer Films via Solvent Vapor Processing: An In Situ GISAXS study 
Macromolecules  2010;43(9):4253-4260.
The real time changes occurring within films of cylinder-forming poly(α-methylstyrene-block-4-hydroxystyrene) (PαMS-b-PHOST) were monitored as they were swollen in tetrahydrofuran (THF) and acetone solvent vapors. In situ information was obtained by combining grazing incidence small angle X-ray scattering (GISAXS) with film thickness monitoring of the solvent vapor swollen films. We show that for self assembly to occur, the polymer thin film must surpass a swollen thickness ratio of 212% of its original thickness when swollen in THF vapors and a ratio of 268% for acetone vapor annealing. As the polymer becomes plasticized by solvent vapor uptake, the polymer chains must become sufficiently mobile to self assemble, or reorganize, at room temperature. Using vapors of a solvent selective to one of the blocks, in our case PHOST-selective acetone, an order-order transition occured driven by the shift in volume fraction. The BCC spherical phase assumed in the highly swollen state can be quenched by rapid drying. Upon treatment with vapor of a non-selective solvent, THF, the film maintained the cylindrical morphology suggested by its dry-state volume fraction. In situ studies indicate that self-assembly occurs spontaneously upon attaining the threshold swelling ratios.
doi:10.1021/ma902646t
PMCID: PMC2992440  PMID: 21116459
11.  Characterization of Lipid-Templated Silica and Hybrid Thin Film Mesophases by Grazing Incidence Small-Angle X-ray Scattering 
The nanostructure of silica and hybrid thin film mesophases templated by phospholipids via an evaporation-induced self-assembly (EISA) process was investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Diacyl phosphatidylcholines with two tails of 6 or 8 carbons were found to template 2D hexagonal mesophases, with the removal of lipid from these lipid/silica films by thermal or UV/O3 processing resulting in a complete collapse of the pore volume. Monoacyl phosphatidylcholines with single tails of 10–14 carbons formed 3D micellular mesophases; the lipid was found to be extractable from these 3D materials, yielding a porous material. In contrast to pure lipid/silica thin film mesophases, films formed from the hybrid bridged silsesquioxane precursor bis(triethoxysilyl)ethane exhibited greater stability toward (both diacyl and monoacyl) lipid removal. Ellipsometric, FTIR, and NMR studies show that the presence of phospholipid suppresses siloxane network formation, while actually promoting condensation reactions in the hybrid material. 1D X-ray scattering and FTIR data were found to be consistent with strong interactions between lipid headgroups and the silica framework.
doi:10.1021/la900748r
PMCID: PMC2736351  PMID: 19496546
12.  Ultra-High Efficiency Photovoltaic Cells for Large Scale Solar Power Generation 
Ambio  2012;41(Suppl 2):125-131.
The primary targets of our project are to drastically improve the photovoltaic conversion efficiency and to develop new energy storage and delivery technologies. Our approach to obtain an efficiency over 40% starts from the improvement of III–V multi-junction solar cells by introducing a novel material for each cell realizing an ideal combination of bandgaps and lattice-matching. Further improvement incorporates quantum structures such as stacked quantum wells and quantum dots, which allow higher degree of freedom in the design of the bandgap and the lattice strain. Highly controlled arrangement of either quantum dots or quantum wells permits the coupling of the wavefunctions, and thus forms intermediate bands in the bandgap of a host material, which allows multiple photon absorption theoretically leading to a conversion efficiency exceeding 50%. In addition to such improvements, microfabrication technology for the integrated high-efficiency cells and the development of novel material systems that realizes high efficiency and low cost at the same time are investigated.
doi:10.1007/s13280-012-0267-4
PMCID: PMC3357770  PMID: 22434438
Multi-junction; Quantum well; Concentrator; Photovoltaic
13.  Mapping DNA Quantity into Electrophoretic Mobility through Quantum Dot Nanotethers for High Resolution Genetic and Epigenetic Analysis 
ACS Nano  2011;6(1):858-864.
Newly discovered nanoparticle properties have driven the development of novel applications and uses. We report a new observation where the electrophoretic mobility of a quantum dot-DNA nanoassembly can be precisely modulated by the degree of surface DNA conjugation. By using streptavidin-coated quantum dots (QD) as nanotethers to gather biotin-labeled DNA into electrophoretic nanoassemblies, the QD surface charge is modulated and transformed into electrophoretic mobility shifts using standard agarose gel electrophoresis. Typical fluorescent assays quantify based on relative intensity. However, this phenomenon uses a novel approach that accurately maps DNA quantity into shifts in relative band position. This property was applied in a quantum dot enabled nanoassay called Quantum Dot Electrophoretic Mobility Shift Assay (QEMSA) that enables accurate quantification of DNA targets down to 1.1-fold (9%) changes in quantity, beyond what is achievable in qPCR. In addition to these experimental findings, an analytical model is presented to explain this behavior. Finally, QEMSA was applied to both genetic and epigenetic analysis of cancer. First, it was used to analyze copy number variation (CNV) of the RSF1/HBXAP gene where conventional approaches for CNV analysis based on comparative genomic hybridization (CGH), microarrays, and qPCR are unable to reliably differentiate less than 2-fold changes in copy number. Then, QEMSA was used for DNA methylation analysis of the p16/CDK2A tumor suppressor gene where its ability to detect subtle changes in methylation was shown to be superior to that of qPCR.
doi:10.1021/nn204377k
PMCID: PMC3273333  PMID: 22136600
Quantum dot; Nanother; DNA; Electrophoretic mobility; Copy number variation; methylation
14.  Entrapment in phospholipid vesicles quenches photoactivity of quantum dots 
Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers.
doi:10.2147/IJN.S22953
PMCID: PMC3173050  PMID: 21931483
fluorescence lifetime; free radicals; liposomes; lipodots; reactive oxygen species
15.  The Development of Quantum Dot Calibration Beads and Quantitative Multicolor Bioassays in Flow Cytometry and Microscopy1 
Analytical biochemistry  2007;364(2):180-192.
The use of fluorescence calibration beads has been the hallmark of quantitative flow cytometry. It has enabled the direct comparison of inter-laboratory data as well as quality control in clinical flow cytometry. In this paper we have described a simple method for producing color-generalizable calibration beads based on streptavidin functionalized quantum dots. Based on their broad absorption spectra and relatively narrow emission, that is tunable on the basis of dot-size, quantum dot calibration beads can be made for any fluorophore that matches their emission color. In an earlier publication(1) we characterized the spectroscopic properties of commercial streptavidin functionalized dots (Invitrogen). Here we describe the molecular assembly of these dots on biotinylated beads. The law of mass action is used to readily define the site densities of the dots on the beads. The applicability of these beads is tested against the industry standard, commercial fluorescein calibration beads. The utility of the calibration beads are also herein extended to the characterization surface densities of dot-labeled epidermal growth factor ligands as well as quantitative indicators of the binding of dot-labeled virus particles to cells.
doi:10.1016/j.ab.2007.02.006
PMCID: PMC2018651  PMID: 17397793
nanotechnology; quantum dots; calibration beads; flow cytometer; quantitation; fluorescence; multiplex; bioassays; virus particles; microscopy; spectroscopy; mass action
16.  Raman scattering of InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces 
Nanoscale Research Letters  2012;7(1):476.
We present a comparative analysis of Raman scattering by acoustic and optical phonons in InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces. Doublets of folded longitudinal acoustic phonons up to the fifth order were observed in the Raman spectra of (001)- and (311)B-oriented quantum dot superlattices measured in polarized scattering geometries. The energy positions of the folded acoustic phonons are well described by the elastic continuum model. Besides the acoustic phonons, the spectra display features related to confined transverse and longitudinal optical as well as interface phonons in quantum dots and spacer layers. Their frequency positions are discussed in terms of phonon confinement, elastic stress, and atomic intermixing.
doi:10.1186/1556-276X-7-476
PMCID: PMC3506502  PMID: 22916827
Raman scattering spectroscopy; Quantum dots, Nanocrystals; Nanoparticles; Phonons
17.  Small-Angle X-Ray Scattering for Imaging of Surface Layers on Intact Bacteria in the Native Environment 
Journal of Bacteriology  2013;195(10):2408-2414.
Crystalline cell surface layers (S-layers) represent a natural two-dimensional (2D) protein self-assembly system with nanometer-scale periodicity that decorate many prokaryotic cells. Here, we analyze the S-layer on intact bacterial cells of the Gram-positive organism Geobacillus stearothermophilus ATCC 12980 and the Gram-negative organism Aquaspirillum serpens MW5 by small-angle X-ray scattering (SAXS) and relate it to the structure obtained by transmission electron microscopy (TEM) after platinum/carbon shadowing. By measuring the scattering pattern of X rays obtained from a suspension of bacterial cells, integral information on structural elements such as the thickness and lattice parameters of the S-layers on intact, hydrated cells can be obtained nondestructively. In contrast, TEM of whole mounts is used to analyze the S-layer lattice type and parameters as well as the physical structure in a nonaqueous environment and local information on the structure is delivered. Application of SAXS to S-layer research on intact bacteria is a challenging task, as the scattering volume of the generally thin (3- to 30-nm) bacterial S-layers is low in comparison to the scattering volume of the bacterium itself. For enhancement of the scattering contrast of the S-layer in SAXS measurement, either silicification (treatment with tetraethyl orthosilicate) is used, or the difference between SAXS signals from an S-layer-deficient mutant and the corresponding S-layer-carrying bacterium is used for determination of the scattering signal. The good agreement of the SAXS and TEM data shows that S-layers on the bacterial cell surface are remarkably stable.
doi:10.1128/JB.02164-12
PMCID: PMC3650539  PMID: 23504021
18.  A Complete Physical Germanium-on-Silicon Quantum Dot Self-Assembly Process 
Scientific Reports  2013;3:2099.
Achieving quantum dot self-assembly at precise pre-defined locations is of vital interest. In this work, a novel physical method for producing germanium quantum dots on silicon using nanoindentation to pre-define nucleation sites is described. Self-assembly of ordered ~10 nm height germanium quantum dot arrays on silicon substrates is achieved. Due to the inherent simplicity and elegance of the proposed method, the results describe an attractive technique to manufacture semiconductor quantum dot structures for future quantum electronic and photonic applications.
doi:10.1038/srep02099
PMCID: PMC3695558  PMID: 23807261
19.  Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field 
Nature Communications  2014;5:3268.
Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain—that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations.
Optical control of nuclear spin polarization in semiconductor quantum dots is promising for applications in NMR imaging. Sallen et al. report efficient dynamic nuclear polarization at zero magnetic field in strain-free gallium arsenide quantum dots with Knight fields dominating the nuclear quadrupole effects.
doi:10.1038/ncomms4268
PMCID: PMC3926008  PMID: 24500329
20.  Quantum Information Processing in the Wall of Cytoskeletal Microtubules 
Journal of Biological Physics  2006;32(5):413-420.
Microtubules (MT) are composed of 13 protofilaments, each of which is a series of two-state tubulin dimers. In the MT wall, these dimers can be pictured as “lattice” sites similar to crystal lattices. Based on the pseudo-spin model, two different location states of the mobile electron in each dimer are proposed. Accordingly, the MT wall is described as an anisotropic two-dimensional (2D) pseudo-spin system considering a periodic triangular “lattice”. Because three different “spin-spin” interactions in each cell exist periodically in the whole MT wall, the system may be shown to be an array of three types of two-pseudo-spin-state dimers. For the above-mentioned condition, the processing of quantum information is presented by using the scheme developed by Lloyd.
doi:10.1007/s10867-006-9025-9
PMCID: PMC2651539  PMID: 19669447
MT; tubulin dimer; 2-D pseudo-spin; “lattice” site; two-state; information processing
21.  Strongly coupled slow-light polaritons in one-dimensional disordered localized states 
Scientific Reports  2013;3:1994.
Cavity quantum electrodynamics advances the coherent control of a single quantum emitter with a quantized radiation field mode, typically piecewise engineered for the highest finesse and confinement in the cavity field. This enables the possibility of strong coupling for chip-scale quantum processing, but till now is limited to few research groups that can achieve the precision and deterministic requirements for these polariton states. Here we observe for the first time coherent polariton states of strong coupled single quantum dot excitons in inherently disordered one-dimensional localized modes in slow-light photonic crystals. Large vacuum Rabi splittings up to 311 μeV are observed, one of the largest avoided crossings in the solid-state. Our tight-binding models with quantum impurities detail these strong localized polaritons, spanning different disorder strengths, complementary to model-extracted pure dephasing and incoherent pumping rates. Such disorder-induced slow-light polaritons provide a platform towards coherent control, collective interactions, and quantum information processing.
doi:10.1038/srep01994
PMCID: PMC3683671  PMID: 23771242
22.  Two-component Dirac-like Hamiltonian for generating quantum walk on one-, two- and three-dimensional lattices 
Scientific Reports  2013;3:2829.
From the unitary operator used for implementing two-state discrete-time quantum walk on one-, two- and three- dimensional lattice we obtain a two-component Dirac-like Hamiltonian. In particular, using different pairs of Pauli basis as position translation states we obtain three different form of Hamiltonians for evolution on one-dimensional lattice. We extend this to two- and three-dimensional lattices using different Pauli basis states as position translation states for each dimension and show that the external coin operation, which is necessary for one-dimensional walk is not a necessary requirement for a walk on higher dimensions but can serve as an additional resource to control the dynamics. The two-component Hamiltonian we present here for quantum walk on different lattices can serve as a general framework to simulate, control, and study the dynamics of quantum systems governed by Dirac-like Hamiltonian.
doi:10.1038/srep02829
PMCID: PMC3789158  PMID: 24088731
23.  Renormalization and small-world model of fractal quantum repeater networks 
Scientific Reports  2013;3:1222.
Quantum networks provide access to exchange of quantum information. The primary task of quantum networks is to distribute entanglement between remote nodes. Although quantum repeater protocol enables long distance entanglement distribution, it has been restricted to one-dimensional linear network. Here we develop a general framework that allows application of quantum repeater protocol to arbitrary quantum repeater networks with fractal structure. Entanglement distribution across such networks is mapped to renormalization. Furthermore, we demonstrate that logarithmical times of recursive such renormalization transformations can trigger fractal to small-world transition, where a scalable quantum small-world network is achieved. Our result provides new insight into quantum repeater theory towards realistic construction of large-scale quantum networks.
doi:10.1038/srep01222
PMCID: PMC3564040  PMID: 23386977
24.  Scherrer grain-size analysis adapted to grazing-incidence scattering with area detectors 
Journal of Applied Crystallography  2009;42(Pt 6):1030-1034.
Various aspects of the application of the Scherrer formula to grain-size analysis in thin films of soft materials are discussed within the methodology of grazing-incidence small- and wide-angle scattering and in conjunction with the use of area detectors.
Ever since its formulation, the Scherrer formula has been the workhorse for quantifying finite size effects in X-ray scattering. Various aspects of Scherrer-type grain-size analysis are discussed with regard to the characterization of thin films with grazing-incidence scattering methods utilizing area detectors. After a brief review of the basic features of Scherrer analysis, a description of resolution-limiting factors in grazing-incidence scattering geometry is provided. As an application, the CHESS D1 beamline is characterized for typical scattering modes covering length scales from the molecular scale to the nanoscale.
doi:10.1107/S0021889809040126
PMCID: PMC2779741  PMID: 19953189
Scherrer formula; grazing-incidence small-angle scattering (GISAXS); grazing-incidence wide-angle scattering (GIWAXS); thin films; soft materials
25.  Three-dimensional dynamics of a fermionic Mott wedding-cake in clean and disordered optical lattices 
Scientific Reports  2013;3:2570.
Non-equilibrium quantum phenomena are ubiquitous in nature. Yet, theoretical predictions on the real-time dynamics of many-body quantum systems remain formidably challenging, especially for high dimensions, strong interactions or disordered samples. Here we consider a notable paradigm of strongly correlated Fermi systems, the Mott phase of the Hubbard model, in a setup resembling ultracold-gases experiments. We study the three-dimensional expansion of a cloud into an optical lattice after removing the confining potential. We use time-dependent density-functional theory combined with dynamical mean-field theory, considering interactions below and above the Mott threshold, as well as disorder effects. At strong coupling, we observe multiple timescales in the melting of the Mott wedding-cake structure, as the Mott plateau persist orders of magnitude longer than the band insulating core. We also show that disorder destabilises the Mott plateau and that, compared to a clean setup, localisation can decrease, creating an interesting dynamic crossover during the expansion.
doi:10.1038/srep02570
PMCID: PMC3759837  PMID: 23999144

Results 1-25 (881228)