The extended states in disordered 1D systems in the presence of the generalized NN-mer correlations

We have been investigating the problem of the Anderson localization in a disordered one dimensional tight-binding model. The disorder is created by the interaction of mobile particles with other species, immobilized at random positions. We introduce a novel method of creating correlations in the optical lattices with such a kind of disorder by using two different lattices with commensurate lattice lengths to hold two species of the particles. Such a model, called the generalized random $N$-mer model leads to the appearance of multiple extended states in contrary to a localization of all states usually expected in one dimension. We develop a method, based on properties of transfer matrices which can be used to determine the presence of extended states and their energies for that class of correlations. Analytical results are compared with the numerical calculations for several cases which can be realized in cold-atom experiments.Comment: 6 pages, 5 figure

Variational Bose-Hubbard model revisited

For strongly interacting bosons in optical lattices the standard description using Bose-Hubbard model becomes questionable. The role of excited bands becomes important. In such a situation we compare results of simulations using multiband Bose-Hubbard model with a recent proposition based on a time dependent variational approach. It is shown that the latter, in its original formulation, uses too small variational space leading often to spurious effects. Possible expansion of variational approach is discussed.Comment: 8 pages, 6 figure

Synthetic Random Flux Model in a periodically-driven optical lattice

We propose a realization of a synthetic Random Flux Model in a two-dimensional optical lattice. Starting from Bose-Hubbard Hamiltonian for two atom species we show how to use fast-periodic modulation of the system parameters to construct random gauge field. We investigate the transport properties of such a system and describe the impact of time-reversal symmetry breaking and correlations in disorder on Anderson localization length.Comment: 6 pages, 4 figure

Role of correlations and off-diagonal terms in binary disordered one dimensional systems

We investigate one dimensional tight binding model in the presence of a correlated binary disorder. The disorder is due to the interaction of particles with heavy immobile other species. Off-diagonal disorder is created by means of a fast periodic modulation of interspecies interaction. The method based on transfer matrix techniques allows us to calculate the energies of extended modes in the correlated binary disorder. We focus on $N$-mer correlations and regain known results for the case of purely diagonal disorder. For off-diagonal disorder we find resonant energies. We discuss ambiguous properties of those states and compare analytical results with numerical calculations. Separately we describe a special case of the dual random dimer model.Comment: 6 pages, 4 figure

Controlling disorder with periodically modulated interactions

We investigate a celebrated problem of one dimensional tight binding model in the presence of disorder leading to Anderson localization from a novel perspective. A binary disorder is assumed to be created by immobile heavy particles for the motion of the lighter, mobile species in the limit of no interaction between mobile particles. Fast periodic modulations of interspecies interactions allow us to produce an effective model with small diagonal and large off-diagonal disorder unexplored in cold atoms experiments. We present an expression for an approximate Anderson localization length and verify the existence of the well known extended resonant mode and analyze the influence of nonzero next-nearest neighbor hopping terms. We point out that periodic modulation of interaction allow disorder to work as a tunable band-pass filter for momenta.Comment: version close to published vesio

Single-particle localization in dynamical potentials

Single particle localization of an ultra-cold atom is studied in one dimension when the atom is confined by an optical lattice and by the incommensurate potential of a high-finesse optical cavity. In the strong coupling regime the atom is a dynamical refractive medium, the cavity resonance depends on the atomic position within the standing-wave mode and nonlinearly determines the depth and form of the incommensurate potential. We show that the particular form of the quasi-random cavity potential leads to the appearance of mobility edges, even in presence of nearest-neighbour hopping. We provide a detailed characterization of the system as a function of its parameters and in particular of the strength of the atom-cavity coupling, which controls the functional form of the cavity potential. For strong atom-photon coupling the properties of the mobility edges significantly depend on the ratio between the periodicities of the confining optical lattice and of the cavity field.Comment: version close to that accepted in Phys. Rev.

Influence of metal objects on measured electromagnetical field intensity of ERS generator

Bakalářská práce pojednává o vlivu kovových předmětů na odchylky měřené intenzity elektromagnetického pole ERS generátoru. V práci jsou ukázány možnosti modelování šíření a odrazu elektromagnetické vlny od reflektoru nebo od zemní plochy v programu Matlab a Comsol Multiphysic. V textu je změřen vliv kovové odrazné plochy na předcertifikační EMC měření ve volném prostranství s ERS a CNE generátorem. Hlavní náplní mé bakalářské práce je ověřit praktickými měřeními teoretické předpoklady a výsledky simulací.The bachelor’s thesis treats influence of metal objects on measured electromagnetical field intensity. There are shown simulation possibilities of propagation and reflection of electromagnetic waves from reflector or ground plane in program Matlab and Comsol Multiphysic in this project. Measurement of the impact of the metal reflecting surfaces at pre-compliance EMC measurement on the open area test site with the ERS and the CNE generator are shown in this text. The main task of this bachelor’s thesis is the verification of theoretical basics and computer simulations by practical experiments.