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Photonic modes exhibiting a polarization winding akin to a vortex possess an integer topological charge. Lasing with topological charge 1 or 2 can be realized in periodic lattices of up to six-fold rotational symmetry. Higher order charges require symmetries not compatible with any two-dimensional Bravais lattice. Here, we experimentally demonstrate lasing with topological charges as high as -5, +7, -17 and +19 in quasicrystals. We discover rich ordered structures of increasing topological charges in the reciprocal space. Our quasicrystal design utilizes group theory in determining electromagnetic field nodes, where lossy plasmonic nanoparticles are positioned to maximize gain. Our results open a new path for fundamental studies of higher-order topological defects, coherent light beams of high topological charge, and realizations of omni-directional, flat-band-like lasing.

We theoretically predict the full quantum geometric tensor, comprising the quantum metric and the Berry curvature, for a square lattice of plasmonic nanoparticles. The gold nanoparticles act as dipole or multipole antenna radiatively coupled over long distances. The photonic-plasmonic eigenfunctions and energies of the system depend on momentum and polarization (pseudospin), and their topological properties are encoded in the quantum geometric tensor. By T-matrix numerical simulations, we identify a TE-TM band splitting at the diagonals of the first Brillouin zone, that is not predicted by the empty lattice band structure nor by the highly symmetric nature of the system. Further, we find quantum metric around these regions of the reciprocal space, and even a non-zero Berry curvature despite the trivial lattice geometry and absence of magnetic field. We show that this non-zero Berry curvature arises exclusively from non-Hermitian effects which break the time-reversal symmetry. The quantum metric, in contrast, originates from a pseudospin-orbit coupling given by the polarization and directional dependence of the radiation., Comment: Revised version

We experimentally observe the quantum geometric tensor, namely the quantum metric and the Berry curvature, for a square lattice of radiatively coupled plasmonic nanoparticles. We observe a non-zero Berry curvature and show that it arises solely from non-Hermitian effects. The quantum metric is found to originate from a pseudospin-orbit coupling. The long-range nature of the radiative interaction renders the behavior distinct from tight-binding systems: Berry curvature and quantum metric are centered around high-symmetry lines of the Brillouin zone instead of high-symmetry points. Our results inspire new pathways in the design of topological systems by tailoring losses or gain., Comment: Revised version

We present a photoluminescence (PL) and Raman spectroscopy study of various diamond samples that have high concentrations of nitrogen-vacancy (NV) color centers up to multiple parts per million (ppm). With green red, and near infrared (NIR) light excitation, we demonstrate that while for samples with a low density of NV centers the signals are primarily dominated by Raman scattering from the diamond lattice, for higher density of NVs we observe a combination of Raman scattering from the diamond lattice and fluorescence from the NV centers, while for the highest NV densities the Raman signals from diamond are completely overwhelmed by the intense NVs fluorescence. However, under NIR excitation, Raman diamond signatures can be observed for some diamonds. These observations reveal different roles of two mechanisms of light emission and contradict the naive belief that Raman scattering enables complete characterisation of a diamond crystalline sample.

We report first-order spatial and temporal correlations in strongly coupled plasmonic Bose-Einstein condensates. The condensate is large, more than twenty times the spatial coherence length of the polaritons in the uncondensed system and hundred times the healing length, making plasmonic lattices an attractive platform for studying long-range spatial correlations in two dimensions (2D). We find that both spatial and temporal coherence display non-exponential decay; the results suggest power-law or stretched exponential behaviour with different exponents for spatial and temporal correlation decays., Comment: 13 pages, 16 figures

Polarization textures of light may reflect fundamental phenomena such as topological defects, and can be utilized in engineering light beams. Three main routes are applied during their creation: spontaneous appearance in phase transitions, steering by an excitation beam, or structural engineering of the medium. We present an approach that uses all three in a platform offering advantages that are not simultaneously provided in any previous system: advanced structural engineering, strong-coupling condensate with effective photonic interactions, as well as room temperature and sub-picosecond operation. We demonstrate domain wall polarization textures in a plasmonic lattice Bose-Einstein condensate, by combining the dipole structure of the lattice with a non-trivial condensate phase revealed by phase retrieval. These results open new prospects for fundamental studies of non-equilibrium condensation and sources of polarization-structured beams., Comment: 29 pages, 7 figures

In this paper, we develop a numerical resolution of the space-time fractional advection-dispersion equation. After time discretization, we utilize collocation technique and implement a product integration method in order to simplify the evaluation of the terms involving spatial fractional order derivatives. Then utilizing Bernstein polynomials as basis, the problem is transformed into a linear system of algebraic equations. Error analysis and order of convergence for the proposed method are also discussed. Some numerical experiments are presented to demonstrate the effectiveness of the proposed method and to confirm the analytic results., Comment: 13 pages

In the papers dealing with derivation and applications of operational matrices of Bernstein polynomials, a basis transformation, commonly a transformation to power basis, is used. The main disadvantage of this method is that the transformation may be ill-conditioned. Moreover, when applied to the numerical simulation of a functional differential equation, it leads to dense operational matrices and so a dense coefficient matrix is obtained. In this paper, we present a new property for Bernstein polynomials. Using this property, we build exact banded operational matrices for derivatives of Bernstein polynomials. Next, as an application, we propose a new numerical method based on a Petrov-Galerkin variational formulation and the new operational matrices utilizing the dual Bernstein basis for the time-fractional advection-dispersion equation. Finally, we show that the proposed method leads to a narrow-banded linear system and so less computational effort is required to obtain the desired accuracy for the approximate solution. Some numerical examples are provided to demonstrate the efficiency of the method., Comment: 19 pages submitted to Numerical Algorithms

We investigate the continuum q-Potts model at its transition point from the disordered to the ordered regime, with particular emphasis on the coexistence of disordered and ordered phases in the high-q case. We argue that occurrence of phase transition can be seen as percolation in the related random cluster representation, similarly to the lattice Potts model, and investigate the typical structure of clusters for high q. We also report on numerical simulations in two dimensions using a continuum version of the Swendsen-Wang algorithm, compare the results with earlier simulations which used the invaded cluster algorithm, and discuss implications on the geometry of clusters in the disordered and ordered phases., Comment: 24 pages, 16 figures

We have experimentally demonstrated pumping of Cooper pairs in a single-island mesoscopic structure. The island was connected to leads through SQUID (Superconducting Quantum Interference Device) loops. Synchronized flux and voltage signals were applied whereby the Josephson energies of the SQUIDs and the gate charge were tuned adiabatically. From the current-voltage characteristics one can see that the pumped current increases in 1e steps which is due to quasiparticle poisoning on the measurement time scale, but we argue that the transport of charge is due to Cooper pairs., Comment: 4 pages

Continuing improvement in processing speed has made it feasible to solve the Reynolds-Averaged Navier-Stokes equations for simple three-dimensional flows on advanced workstations. Combining multiple workstations into a network-based heterogeneous parallel computer allows the application of programming principles learned on MIMD (Multiple Instruction Multiple Data) distributed memory parallel computers to the solution of larger problems. An overset-grid flow solution code has been developed which uses a cluster of workstations as a network-based parallel computer. Inter-process communication is provided by the Parallel Virtual Machine (PVM) software. Solution speed equivalent to one-third of a Cray-YMP processor has been achieved from a cluster of nine commonly used engineering workstation processors. Load imbalance and communication overhead are the principal impediments to parallel efficiency in this application.