352 research outputs found
Enhanced Diffusion of a Needle in a Planar Course of Point Obstacles
The transport of an infinitely thin, hard rod in a random, dense array of
point obstacles is investigated by molecular dynamics simulations. Our model
mimics the sterically hindered dynamics in dense needle liquids. The
center-of-mass diffusion exhibits a minimum, and transport becomes increasingly
fast at higher densities. The diffusion coefficient diverges according to a
power law in the density with an approximate exponent of 0.8. This observation
is connected with a new divergent time scale, reflected in a zig-zag motion of
the needle, a two-step decay of the velocity-autocorrelation function, and a
negative plateau in the non-Gaussian parameter.Comment: accepted for publication in Phys. Rev. Let
Space-resolved dynamics of a tracer in a disordered solid
The dynamics of a tracer particle in a glassy matrix of obstacles displays
slow complex transport as the free volume approaches a critical value and the
void space falls apart. We investigate the emerging subdiffusive motion of the
test particle by extensive molecular dynamics simulations and characterize the
spatio-temporal transport in terms of two-time correlation functions, including
the time-dependent diffusion coefficient as well as the wavenumber-dependent
intermediate scattering function. We rationalize our findings within the
framework of critical phenomena and compare our data to a dynamic scaling
theory.Comment: 10 pages, 7 figures, submitted to Journal of Non-Crystalline Solid
Coherence dynamics and quantum-to-classical crossover in an exciton-cavity system in the quantum strong coupling regime
Interaction between light and matter generates optical nonlinearities, which are particularly pronounced in the quantum strong coupling regime. When a single bosonic mode couples to a single fermionic mode, a Jaynes-Cummings (JC) ladder is formed, which we realize here using cavity photons and quantum dot excitons. We measure and model the coherent anharmonic response of this strongly coupled exciton-cavity system at resonance. Injecting two photons into the cavity, we demonstrate a root 2 larger polariton splitting with respect to the vacuum Rabi splitting. This is achieved using coherent nonlinear spectroscopy, specifically four-wave mixing, where the coherence between the ground state and the first (second) rung of the JC ladder can be interrogated for positive (negative) delays. With increasing excitation intensity and thus rising average number of injected photons, we observe spectral signatures of the quantum-to-classical crossover of the strong coupling regime.Peer reviewe
Nonlinear photoluminescence spectra from a quantum dot-cavity system: Direct evidence of pump-induced stimulated emission and anharmonic cavity-QED
We investigate the power-dependent photoluminescence spectra from a strongly
coupled quantum dot-cavity system using a quantum master equation technique
that accounts for incoherent pumping, pure dephasing, and fermion or boson
statistics. Analytical spectra at the one-photon correlation level and the
numerically exact multi-photon spectra for fermions are presented. We compare
to recent experiments on a quantum dot-micropiller cavity system and show that
an excellent fit to the data can be obtained by varying only the incoherent
pump rates in direct correspondence with the experiments. Our theory and
experiments together show a clear and systematic way of studying
stimulated-emission induced broadening and anharmonic cavity-QED.Comment: We have reworked our previous arXiv paper and submitted this latest
version for peer revie
The Localization Transition of the Two-Dimensional Lorentz Model
We investigate the dynamics of a single tracer particle performing Brownian
motion in a two-dimensional course of randomly distributed hard obstacles. At a
certain critical obstacle density, the motion of the tracer becomes anomalous
over many decades in time, which is rationalized in terms of an underlying
percolation transition of the void space. In the vicinity of this critical
density the dynamics follows the anomalous one up to a crossover time scale
where the motion becomes either diffusive or localized. We analyze the scaling
behavior of the time-dependent diffusion coefficient D(t) including corrections
to scaling. Away from the critical density, D(t) exhibits universal
hydrodynamic long-time tails both in the diffusive as well as in the localized
phase.Comment: 13 pages, 7 figures
Analysis Of Parity Between Protein-based Electrophoretic Methods For The Characterization Of Oral Candida Species.
Electrophoretic studies of multilocus-enzymes (MLEE) and whole-cell protein (SDS-PAGE) were carried out in order to evaluate the parity between different methods for the characterization of five Candida species commonly isolated from oral cavity of humans by numerical taxonomy methods. The obtained data revealed that sodium dodecyl sulfate polyacrylamide gel electrophoresis is more efficient in grouping strains in their respective species while MLEE has much limited resolution in organizing all strains in their respective species-specific clusters. MLEE technique must be regarded for surveys in which just one species of Candida is involved.95801-
Exciton-polariton trapping and potential landscape engineering
Exciton-polaritons in semiconductor microcavities have become a model system for the studies of dynamical Bose-Einstein condensation, macroscopic coherence, many-body effects, nonclassical states of light and matter, and possibly quantum phase transitions in a solid state. These low-mass bosonic quasiparticles can condense at comparatively high temperatures up to 300 K, and preserve the fundamental properties of the condensate, such as coherence in space and time domain, even when they are out of equilibrium with the environment. Although the presence of an in-plane confining potential is not strictly necessary in order to observe Bose-Einstein condensation, engineering of the polariton confinement is a key to controlling, shaping, and directing the flow of polaritons. Prototype polaritonbased optoelectronic devices rely on ultrafast photon-like velocities and strong nonlinearities exhibited by polaritons, as well as on their tailored confinement. Nanotechnology provides several pathways to achieving polariton confinement, and the specific features and advantages of different methods are discussed in this review. Being hybrid exciton-photon quasiparticles, polaritons can be trapped via their excitonic as well as photonic component, which leads to a wide choice of highly complementary trapping techniques. Here we highlight the almost free choice of the confinement strengths and trapping geometries that provide powerful means for control and manipulation of the polariton systems both in the semi-classical and quantum regimes. Furthermore, the possibilities to observe effects of the polariton blockade, Mott insulator physics, and population of higher-order energy bands in sophisticated lattice potentials are discussed. Observation of such effects could lead to realization of novel polaritonic non-classical light sources and quantum simulators.PostprintPeer reviewe
Observation of gain-pinned dissipative solitons in a microcavity laser
This work was supported by the National Science Center in Poland, by Grant Nos. 2016/23/N/ST3/01350 and 2018/30/E/ST7/00648, and by the Polish National Agency for Academic Exchange. The WĂĽrzburg group gratefully acknowledges support by the State of Bavaria. The work at the Australian National University was supported by the Australian Research Council.We demonstrate an experimental approach for creating spatially localized states in a semiconductor microcavity laser. In particular, we shape the spatial gain profile of a quasi-one-dimensional microcavity laser with a nonresonant, pulsed optical pump to create spatially localized structures, known as gain-pinned dissipative solitons, that exist due to the balance of gain and nonlinear losses. We directly probe the ultrafast formation dynamics and decay of these localized structures, showing that they are created on a picosecond timescale, orders of magnitude faster than laser cavity solitons. All of the experimentally observed features and dynamics are reconstructed by numerical modeling using a complex Ginzburg-Landau model, which explicitly takes into account the carrier density dynamics in the semiconductor.Publisher PDFPeer reviewe
- …