Full control by locally induced relaxation

We demonstrate a scheme for controlling a large quantum system by acting on a small subsystem only. The local control is mediated to the larger system by some fixed coupling Hamiltonian. The scheme allows to transfer arbitrary and unknown quantum states from a memory on the large system (``upload access'') as well as the inverse (``download access''). We study sufficient conditions of the coupling Hamiltonian and give lower bounds on the fidelities for downloading and uploading.Comment: 4 pages, 2 figure

The Generalized Lyapunov Theorem and its Application to Quantum Channels

We give a simple and physically intuitive necessary and sufficient condition for a map acting on a compact metric space to be mixing (i.e. infinitely many applications of the map transfer any input into a fixed convergency point). This is a generalization of the "Lyapunov direct method". First we prove this theorem in topological spaces and for arbitrary continuous maps. Finally we apply our theorem to maps which are relevant in Open Quantum Systems and Quantum Information, namely Quantum Channels. In this context we also discuss the relations between mixing and ergodicity (i.e. the property that there exist only a single input state which is left invariant by a single application of the map) showing that the two are equivalent when the invariant point of the ergodic map is pure.Comment: 13 pages, 3 figure

Pollutant dispersion in a developing valley cold-air pool

Pollutants are trapped and accumulate within cold-air pools, thereby affecting air quality. A numerical model is used to quantify the role of cold-air-pooling processes in the dispersion of air pollution in a developing cold-air pool within an alpine valley under decoupled stable conditions. Results indicate that the negatively buoyant downslope flows transport and mix pollutants into the valley to depths that depend on the temperature deficit of the flow and the ambient temperature structure inside the valley. Along the slopes, pollutants are generally entrained above the cold-air pool and detrained within the cold-air pool, largely above the ground-based inversion layer. The ability of the cold-air pool to dilute pollutants is quantified. The analysis shows that the downslope flows fill the valley with air from above, which is then largely trapped within the cold-air pool, and that dilution depends on where the pollutants are emitted with respect to the positions of the top of the ground-based inversion layer and cold-air pool, and on the slope wind speeds. Over the lower part of the slopes, the cold-air-pool-averaged concentrations are proportional to the slope wind speeds where the pollutants are emitted, and diminish as the cold-air pool deepens. Pollutants emitted within the ground-based inversion layer are largely trapped there. Pollutants emitted farther up the slopes detrain within the cold-air pool above the ground-based inversion layer, although some fraction, increasing with distance from the top of the slopes, penetrates into the ground-based inversion layer.Peer reviewe

Influence of along-valley terrain heterogeneity on exchange processes over idealized valleys

Idealized numerical simulations of thermally driven flows over various valley–plain topographies are performed under daytime conditions. Valley floor inclination and narrowing valley cross sections are systematically varied to study the influence of along-valley terrain heterogeneity on the developing boundary layer structure, as well as horizontal and vertical transport processes. Valley topographies with inclined valley floors of 0.86° increase upvalley winds by a factor of about 1.9 due to smaller valley volumes (volume effect) and by a factor of about 1.6 due to additional upslope buoyancy forces. Narrowing the valley cross section by 20 km per 100 km along-valley distance increases upvalley winds by a factor of about 2.6. Vertical mass fluxes out of the valley are strongly increased by a factor between 1.8 and 2.8 by narrowing the valley cross sections and by a factor of 1.2 by inclining the valley floor. Trajectory analysis shows intensified horizontal transport of parcels from the foreland into the valley within the boundary layer in cases with inclined floors and narrowing cross sections due to increased upvalley winds

Valley floor inclination affecting valley winds and transport of passive tracers in idealised simulations

In mountainous regions, diurnal thermally driven winds impact daily weather and air quality. This study investigates how the inclination of idealised valleys affects these winds and the transport of passive tracers using high-resolution numerical simulations with the Weather Research and Forecasting (WRF) model. We explore a range of valley inclinations from 0 to 2.28°, bridging the gap between previous studies on flat and moderately inclined (up to 0.86°) idealised valleys and steeper (2–5°) real Himalayan valleys. We find that during daytime in the inclined valleys, up-valley winds penetrate deeper into the valleys and become stronger, up to a critical inclination beyond which the winds weaken. The flat-floored valley exhibits the strongest night-time down-valley winds overall, but surface-based down-valley winds are more prominent in inclined valleys. Steeper valleys enhance the vertical transport of passive tracers, resulting in ventilation at higher altitudes compared to the flat-floored valley. Despite stronger overall tracer outflow in the flat-floored valley, this occurs at lower altitudes, leading to most of the ventilated tracers being accumulated in the lowest few kilometres of the atmosphere. Consequently, steeper valleys are more efficient at ventilating tracers to the upper troposphere, which would, for example, lead to higher potential for long-range transport. These findings underscore the critical role of valley geometry in shaping wind patterns and pollutant transport, providing valuable insights for improving transport modelling in mountainous regions.</p

Spatial distribution of aerosols in the Inn Valley atmosphere during wintertime

This study analyzes the structure of the wintertime boundary layer in an Alpine valley (Inn Valley, Austria) for a case of high air pollution. We present airborne aerosol observations collected with particle counters and a backscatter lidar. The effect of upslope winds on the spatial distribution of pollutants is investigated. An asymmetry in the aerosol distribution is observed in the cross-valley direction which presumably is related to differences in orientation and albedo of the two valley slopes. A one-sided thermal circulation, which develops above the sun-exposed slope, is most likely responsible for the observed redistribution of aerosols during daytime. Elevated aerosol layers form at the height of shallow inversion layers. Despite this vertical transport of pollutants by slope winds, no effective vertical venting of the polluted air mass into the free atmosphere can be achieved

A multimethodological approach to study the spatial distribution of air pollution in an Alpine valley during wintertime

In order to investigate the spatial distribution of air pollutants in the Inn valley (Tyrol, Austria) during wintertime, a joint field campaign of the three research projects ALPNAP (Monitoring and Minimisation of Traffic-Induced Noise and Air Pollution Along Major Alpine Transport Routes), INNAP (Boundary Layer Structure in the Inn Valley during high Air Pollution) and INNOX (NOx-structure in the Inn Valley during High Air Pollution) was carried out in January/February 2006. In addition to continuous ground based measurements, vertical profiles of various air pollutants and meteorological parameters were obtained on six selected days. For in-situ investigations, a tethered balloon was used to analyse the lowest atmospheric layers, 0�500 m above the valley bottom (a.v.b.), and a research aircraft sampled at 150�2200 m a.v.b. An aircraft equipped with an aerosol backscatter lidar performed nadir measurements at 3000 m a.v.b. Combined results from a typical day show a strongly polluted layer up to about 125 m a.v.b. in the morning. Around midday concentrations on the valley floor decrease indicating some vertical air exchange despite thermally stable conditions. Strong vertical and horizontal gradients with enhanced pollution levels along the sunny side of the valley up to 1300 m a.v.b. were observed in the afternoon. This vertical mixing due to thermally or dynamically driven slope winds reduces the concentration of air pollutants at the bottom of the valley and causes the formation of elevated pollution layers

Air Pollution Transport in an Alpine Valley: Results From Airborne and Ground-Based Observations

An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current, back-and-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type, upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers