Probing microscopic models for system-bath interactions via parametric driving

We show that strong parametric driving of a quantum harmonic oscillator coupled to a thermal bath allows one to distinguish between different microscopic models for the oscillator-bath coupling. We consider a bath with an Ohmic spectral density and a model where the system-bath interaction can be tuned continuously between position and momentum coupling via the coupling angle $\alpha$. We derive a master equation for the reduced density operator of the oscillator in Born-Markov approximation and investigate its quasi-steady state as a function of the driving parameters, the temperature of the bath and the coupling angle $\alpha$. We find that the time-averaged variance of position and momentum exhibits a strong dependence on these parameters. In particular, we identify parameter regimes that maximise the $\alpha$-dependence and provide an intuitive explanation of our results.Comment: 13 pages, 8 figure

Optical control of the current-voltage relation in stacked superconductors

We simulate the current-voltage relation of short layered superconductors, which we model as stacks of capacitively coupled Josephson junctions. The system is driven by external laser fields, in order to optically control the voltage drop across the junction. We identify parameter regimes in which supercurrents can be stabilised against thermally induced phase slips, thus reducing the effective voltage across the superconductor. Furthermore, single driven Josephson junctions are known to exhibit phase-locked states, where the superconducting phase is locked to the driving field. We numerically observe their persistence in the presence of thermal fluctuations and capacitive coupling between adjacent Josephson junctions. Our results indicate how macroscopic material properties can be manipulated by exploiting the large optical nonlinearities of Josephson plasmons.Comment: 7 pages, 7 figure

Corruption and Environmental Policy: An Alternative Perspective

We construct an overlapping generations model in which agents live through two periods; childhood and adulthood. Each agent makes choices only as an adult, based on her utility that depends on her own consumption and the human capital and environmental quality endowed to her offspring. Entering adulthood, agents choose randomly between two occupations: citizens and politicians. Citizens are the only producers of a single good and choose the proportion of their income to declare to the tax authorities. Politicians decide upon the allocation of the tax revenue between environmental protection and education activities, taking as given the rates of peculation in each activity. In this context, two self-fulfilling stable equilibria can emerge, one associated with high and another with low corruption. Corrupted politicians induce high levels of tax evasion, reducing total public funds and thus environmental protection activities. This result is in accordance with existing empirical evidence and implies that environmental policies may fail in corrupt countries where they are used as means of supporting rent seeking activities instead of protecting the environment. A higher level political authority could intervene and force the low corruption equilibrium by choosing the appropriate tax rate and, through institutional changes, the rates of peculation.Corruption, Environmental Policy

Thermalization of holographic Wilson loops in spacetimes with spatial anisotropy

In this paper, we study behaviour of Wilson loops in the boost-invariant nonequilibrium anisotropic quark-gluon plasma produced in heavy-ion collisions within the holographic approach. We describe the thermalization studying the evolution of the Vaidya metric in the boost-invariant and spatially anisotropic background. To probe the system during this process we calculate rectangular Wilson loops oriented in different spatial directions. We find that anisotropic effects are more visible for the Wilson loops lying in the transversal plane unlike the Wilson loops with partially longitudinal orientation. In particular, we observe that the Wilson loops can thermalizes first unlike to the order of the isotropic model. We see that Wilson loops on transversal contours have the shortest thermalization time. We also calculate the string tension and the pseudopotential at different temperatures for the static quark-gluon plasma. We show that the pseudopotential related to the configuration on the transversal plane has the screened Cornell form. We also show that the jet-quenching parameter related with the average of the light-like Wilson loop exhibits the dependence on orientations.Comment: 39 pages, 12 figures; v3: typos corrected, to appear in Nucl. Phys.

Comparison and evaluation of global publicly available bathymetry grids in the Arctic

In this study we evaluate the differences between six publicly available bathymetry grids in different regions of the Arctic. The independent, high-resolution and accuracy multibeam sonar derived grids are used as a ground truth against which the analyzed grids are compared. The specific bathymetry grids assessed, IBCAO, GEBCO 1 minute, GEBCO_08, ETOPO1, SRTM30_Plus, and Smith and Sandwell, are separated into two major Types: Type A, grids based solely on sounding data sources, and Type B, grids based on sounding data combined with gravity data. The differences were evaluated in terms of source data accuracy, depth accuracy, internal consistency, presence of artifacts, interpolation accuracy, registration issues and resolution of the coastline. These parameters were chosen as quality metrics important for the choice of the grid for any given purpose. We find that Type A bathymetry grids (in particular GEBCO_08) perform better than Type B grids in terms of internal consistency, and have higher accuracy in the different morphological provinces, especially the continental shelf, mainly due to the better source data coverage. Type B grids, on the other hand, have pronounced artifacts and have low accuracy on the shelf due to the scarcity of source data in the region and, in general, the poor performance of gravity prediction in shallow areas and high latitudes. Finally, we propose qualitative metrics that are important when choosing a bathymetry grid and support these metrics with a quality model to guide the choice of the most appropriate grid