Vortex-vortex control in exciton-polariton condensates

Vortices are widely studied in fields ranging from nonlinear optics to magnetic systems and superconductors. A vortex carries a binary information corresponding to its topological charge, `plus' or `minus', that can be used for information storage and processing. In spatially extended optical and condensed many-particle systems, achieving full control over vortex formation and its charge is particularly difficult and is not easily extended to systems of multiple vortices. Here we demonstrate the optical creation of multiplets of phase-locked vortices in polariton condensates using off-resonant excitation with ring-shaped pump beams. We find that the vorticity of one vortex can be controlled solely using the phase-locking with other nearby vortices. Using this mechanism, we demonstrate how an existing vortex with a specific topological charge can be inverted to the oppositely charged state, and how the charge state of one reference vortex can be copied to a neighboring vortex. This way we can optically encode any set of binary information onto a chain of vortices. We further show that this information can be modified later by using the possibility to address and manipulate each vortex in the chain individually.Comment: Physical Review B, in pres

Circular polarization reversal of half-vortex cores in polariton condensates

Vortices are topological objects carrying quantized orbital angular momentum and have been widely studied in many physical systems for their applicability in information storage and processing. In systems with spin degree of freedom the elementary excitations are so called half-vortices, carrying a quantum rotation only in one of the two spin components. We study the spontaneous formation and stability of localized such half-vortices in semiconductor microcavity polariton condensates, non-resonantly excited by a linearly polarized ring-shaped pump. The TE-TM splitting of optical modes in the microcavity system leads to an effective spin-orbit coupling, resulting in solutions with discrete rotational symmetry. The cross-interaction between different spin components provides an efficient method to realize all-optical half-vortex core switching inverting its circular polarization state. This switching can be directly measured in the polarization resolved intensity in the vortex core region and it can also be applied to higher order half-vortex states.Comment: 8 pages, 8 figure

Second-Order Self-Consistent-Field Density-Matrix Renormalization Group

We present a matrix-product state (MPS)-based quadratically convergent density-matrix renormalization group self-consistent-field (DMRG-SCF) approach. Following a proposal by Werner and Knowles (JCP 82, 5053, (1985)), our DMRG-SCF algorithm is based on a direct minimization of an energy expression which is correct to second-order with respect to changes in the molecular orbital basis. We exploit a simultaneous optimization of the MPS wave function and molecular orbitals in order to achieve quadratic convergence. In contrast to previously reported (augmented Hessian) Newton-Raphson and super-configuration-interaction algorithms for DMRG-SCF, energy convergence beyond a quadratic scaling is possible in our ansatz. Discarding the set of redundant active-active orbital rotations, the DMRG-SCF energy converges typically within two to four cycles of the self-consistent procedureComment: 40 pages, 5 figures, 3 table

Regional climate projections in two alpine river basins: Upper Danube and Upper Brahmaputra

Projections from coarse-grid global circulation models are not suitable for regional estimates of water balance or trends of extreme precipitation and temperature, especially not in complex terrain. Thus, downscaling of global to regionally resolved projections is necessary to provide input to integrated water resources management approaches for river basins like the Upper Danube River Basin (UDRB) and the Upper Brahmaputra River Basin (UBRB). This paper discusses the application of the regional climate model COSMO-CLM as a dynamical downscaling tool. To provide accurate data the COSMO-CLM model output was post-processed by statistical means. This downscaling chain performs well in the baseline period 1971 to 2000. However, COSMO-CLM performs better in the UDRB than in the UBRB because of a longer application experience and a less complex climate in Europe. Different climate change scenarios were downscaled for the time period 1960–2100. The projections show an increase of temperature in both basins and for all seasons. The values are generally higher in the UBRB with the highest values occurring in the region of the Tibetan Plateau. Annual precipitation shows no substantial change. However, seasonal amounts show clear trends, for instance an increasing amount of spring precipitation in the UDRB. Again, the largest trends for different precipitation statistics are projected in the region of the Tibetan Plateau. Here, the projections show up to 50% longer dry periods in the months June to September with a simultaneous increase of about 10% for the maximum amount of precipitation on five consecutive days. For the Assam region in India, the projections also show an increase of 25% in the number of consecutive dry days during the monsoon season leading to prolonged monsoon breaks

Approaching the Automation of Cyber Security Testing of Connected Vehicles

The advancing digitalization of vehicles and automotive systems bears many advantages for creating and enhancing comfort and safety-related systems ranging from drive-by-wire, inclusion of advanced displays, entertainment systems up to sophisticated driving assistance and autonomous driving. It, however, also contains the inherent risk of being used for purposes that are not intended for, raging from small non-authorized customizations to the possibility of full-scale cyberattacks that affect several vehicles to whole fleets and vital systems such as steering and engine control. To prevent such conditions and mitigate cybersecurity risks from affecting the safety of road traffic, testing cybersecurity must be adopted into automotive testing at a large scale. Currently, the manual penetration testing processes cannot uphold the increasing demand due to time and cost to test complex systems. We propose an approach for an architecture that (semi-)automates automotive cybersecurity test, allowing for more economic testing and therefore keeping up to the rising demand induced by new vehicle functions as well as the development towards connected and autonomous vehicles.Comment: 3 pages, 1 figure, Central European Cybersecurity Conference 2019 (CECC2019), Munic