Author
Wolfgang Werner Langbein
Other affiliations: Kaiserslautern University of Technology, Technical University of Denmark, Karlsruhe Institute of Technology ...read more
Bio: Wolfgang Werner Langbein is an academic researcher from Cardiff University. The author has contributed to research in topics: Quantum dot & Exciton. The author has an hindex of 54, co-authored 396 publications receiving 10439 citations. Previous affiliations of Wolfgang Werner Langbein include Kaiserslautern University of Technology & Technical University of Denmark.
Topics: Quantum dot, Exciton, Dephasing, Biexciton, Quantum well
Papers published on a yearly basis
Papers
More filters
TL;DR: Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic exciton-acoustic phonon interactions.
Abstract: We measure a dephasing time of several hundred picoseconds at low temperature in the ground-state transition of strongly confined InGaAs quantum dots, using a highly sensitive four-wave mixing technique. Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic exciton-acoustic phonon interactions.
896 citations
TL;DR: In this paper, the authors propose and investigate the potential of polariton graphs as an efficient analogue simulator for finding the global minimum of the XY model by imprinting polariton condensate lattices of bespoke geometries.
Abstract: The vast majority of real-life optimization problems with a large number of degrees of freedom are intractable by classical computers, since their complexity grows exponentially fast with the number of variables. Many of these problems can be mapped into classical spin models, such as the Ising, the XY or the Heisenberg models, so that optimization problems are reduced to finding the global minimum of spin models. Here, we propose and investigate the potential of polariton graphs as an efficient analogue simulator for finding the global minimum of the XY model. By imprinting polariton condensate lattices of bespoke geometries we show that we can engineer various coupling strengths between the lattice sites and read out the result of the global minimization through the relative phases. Besides solving optimization problems, polariton graphs can simulate a large variety of systems undergoing the U(1) symmetry-breaking transition. We realize various magnetic phases, such as ferromagnetic, anti-ferromagnetic, and frustrated spin configurations on a linear chain, the unit cells of square and triangular lattices, a disordered graph, and demonstrate the potential for size scalability on an extended square lattice of 45 coherently coupled polariton condensates. Our results provide a route to study unconventional superfluids, spin liquids, Berezinskii–Kosterlitz–Thouless phase transition, and classical magnetism, among the many systems that are described by the XY Hamiltonian.
278 citations
TL;DR: The potential of polariton graphs are investigated as an efficient analogue simulator for finding the global minimum of the XY model and provide a route to study unconventional superfluids, spin liquids, Berezinskii-Kosterlitz-Thouless phase transition, and classical magnetism, among the many systems described by the XY Hamiltonian.
Abstract: Several platforms are currently being explored for simulating physical systems whose complexity increases faster than polynomially with the number of particles or degrees of freedom in the system. Defects and vacancies in semiconductors or dielectric materials, magnetic impurities embedded in solid helium \cite{lemeshko13}, atoms in optical lattices, photons, trapped ions and superconducting q-bits are among the candidates for predicting the behaviour of spin glasses, spin-liquids, and classical magnetism among other phenomena with practical technological applications. Here we investigate the potential of polariton graphs as an efficient simulator for finding the global minimum of the $XY$ Hamiltonian. By imprinting polariton condensate lattices of bespoke geometries we show that we can simulate a large variety of systems undergoing the U(1) symmetry breaking transitions. We realise various magnetic phases, such as ferromagnetic, anti-ferromagnetic, and frustrated spin configurations on unit cells of various lattices: square, triangular, linear and a disordered graph. Our results provide a route to study unconventional superfluids, spin-liquids, Berezinskii-Kosterlitz-Thouless phase transition, classical magnetism among the many systems that are described by the $XY$ Hamiltonian.
243 citations
TL;DR: In this article, measurements and calculations of optical Rabi oscillations in the excitonic ground-state transition of an InGaAs quantum dot ensemble at low temperature are presented.
Abstract: We present measurements and calculations of optical Rabi oscillations in the excitonic ground-state transition of an InGaAs quantum dot ensemble at low temperature. Rabi oscillations which are damped versus pulse area and change period when changing pulse duration are observed. Comparisons with calculations show that the observed damping is not intrinsic to a single dot. Dephasing processes and the biexciton resonance change the amplitude and the period of the oscillations, respectively, while the damping versus pulse area is due to a distribution of transition dipole moments in the ensemble.
185 citations
TL;DR: In this article, the distribution of the fine-structure splitting and the biexciton binding energy were measured in a series of annealed InAs quantum dots, and the authors found a decrease of the binding energy with increasing annealing temperature, indicating a symmetrizing of the in-plane confinement potential.
Abstract: The distribution of the fine-structure splitting ħδ1 and of the biexciton binding energy ħδB are measured in a series of annealed InAs quantum dots. We find a decrease of ħδ1 from 96μeV to 6μeV with increasing annealing temperature, indicating a symmetrizing of the in-plane confinement potential. The biexciton binding energy shows only a weak dependence on the confinement energy, which we attribute to a compensation between decreasing confinement and decreasing separation of electron and hole.
183 citations
Cited by
More filters
28 Jul 2005
TL;DR: PfPMP1）与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。
18,940 citations
TL;DR: In this article, the authors present a comprehensive, up-to-date compilation of band parameters for the technologically important III-V zinc blende and wurtzite compound semiconductors.
Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.
6,349 citations
TL;DR: The emerging ability to control the patterns of matter on the nanometer length scale can be expected to lead to entirely new types of biological sensors capable of sensing at the single-molecule level in living cells, and capable of parallel integration for detection of multiple signals.
Abstract: In the coming decade, the ability to sense and detect the state of biological systems and living organisms optically, electrically and magnetically will be radically transformed by developments in materials physics and chemistry. The emerging ability to control the patterns of matter on the nanometer length scale can be expected to lead to entirely new types of biological sensors. These new systems will be capable of sensing at the single-molecule level in living cells, and capable of parallel integration for detection of multiple signals, enabling a diversity of simultaneous experiments, as well as better crosschecks and controls.
2,960 citations
TL;DR: The synthesis of epitaxially grown, wurtzite CdSe/CdS core/shell nanocrystals is reported in this paper, where shells of up to three monolayers in thickness were grown on cores ranging in diameter from 23 to 39.
Abstract: The synthesis of epitaxially grown, wurtzite CdSe/CdS core/shell nanocrystals is reported Shells of up to three monolayers in thickness were grown on cores ranging in diameter from 23 to 39 A Shell growth was controllable to within a tenth of a monolayer and was consistently accompanied by a red shift of the absorption spectrum, an increase of the room temperature photoluminescence quantum yield (up to at least 50%), and an increase in the photostability Shell growth was shown to be uniform and epitaxial by the use of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and optical spectroscopy The experimental results indicate that in the excited state the hole is confined to the core and the electron is delocalized throughout the entire structure The photostability can be explained by the confinement of the hole, while the delocalization of the electron results in a degree of electronic accessibility that makes these nanocrystals
2,584 citations