Multi-phonon relaxation and generation of quantum states in a nonlinear mechanical oscillator

The dissipative quantum dynamics of an anharmonic oscillator is investigated theoretically in the context of carbon-based nano-mechanical systems. In the short-time limit, it is known that macroscopic superposition states appear for such oscillators. In the long-time limit, single and multi-phonon dissipation lead to decoherence of the non-classical states. However, at zero temperature, as a result of two-phonon losses the quantum oscillator eventually evolves into a non-classical steady state. The relaxation of this state due to thermal excitations and one-phonon losses is numerically and analytically studied. The possibility of verifying the occurrence of the non-classical state is investigated and signatures of the quantum features arising in a ring-down setup are presented. The feasibility of the verification scheme is discussed in the context of quantum nano-mechanical systems.Comment: 23 pages, 8 figures; Minor revisions; Accepted for publication in NJ

Nonlinear-dissipation-induced entanglement of coupled nonlinear oscillators

The quantum dynamics of two weakly coupled nonlinear oscillators is analytically and numerically investigated in the context of nonlinear dissipation. The latter facilitates the creation and preservation of nonclassical steady states. Starting from a microscopic description of two oscillators individually interacting with their dissipative environments, it is found that in addition to energy relaxation, dephasing arises due to the mutual coupling. Using the negativity as an entanglement measure, it is shown that the coupling entangles the oscillators in the long-time limit. For finite temperatures, entanglement sudden death and rebirth are observed

Entanglement dynamics of quantum oscillators nonlinearly coupled to thermal environments

We study the asymptotic entanglement of two quantum harmonic oscillators nonlinearly coupled to an environment. Coupling to independent baths and a common bath are investigated. Numerical results obtained using the Wangsness-Bloch-Redfield method are supplemented by analytical results in the rotating wave approximation. The asymptotic negativity as function of temperature, initial squeezing, and coupling strength, is compared to results for systems with linear system-reservoir coupling. We find that, due to the parity-conserving nature of the coupling, the asymptotic entanglement is considerably more robust than for the linearly damped cases. In contrast to linearly damped systems, the asymptotic behavior of entanglement is similar for the two bath configurations in the nonlinearly damped case. This is due to the two-phonon system-bath exchange causing a suppression of information exchange between the oscillators via the bath in the common-bath configuration at low temperatures

Mechanical cat states in graphene resonators

We study the quantum dynamics of a symmetric nanomechanical graphene resonator with degenerate flexural modes. Applying voltage pulses to two back gates, flexural vibrations of the membrane can be selectively actuated and manipulated. For graphene, nonlinear response becomes important already for amplitudes comparable to the magnitude of zero point fluctuations. We show, using analytical and numerical methods, that this allows for creation of cat-like superpositions of coherent states as well as superpositions of coherent cat-like non-product states.Comment: 4 pages, 3 figure

Automatic construction of verb valency patterns for Slovene

Natural language processing greatly depends on a sufficient amount of training data. When handling with smaller datasets, we can enrich our data by analyzing the semantic structure of the language. In our thesis, we will be working with valency. Valency carries information about the meaning of a sentence. While valency is usually a feature of verbs, we can also observe it in adjectives and nouns. Valency forms valency patterns around carriers. In theory, each sense of the valency carrier should form a distinguishable valency pattern. Valency patterns have a small feature space and are fit for training machine learning algorithms. They contain enough information to distinguish the sense of the valency carrier. Our work is based on corpus ssj500k 2.1. Over half of the corpus contains hand-annotated semantic roles from which we extracted valency patterns. We built a program for listing and analyzing the valency patterns. In theory, different verb senses form different valency patterns. We tested a number of clustering algorithms on the corpus sentences. The goal was to cluster the valency frames, based on similar senses, and to find sense specific valency patterns. We implemented three versions of Lesk algorithm and two versions of k-means algorithm. We used data from SloWNet and SSKJ for the knowledge based Lesk algorithms

Die geostrategische Bedeutung Afghanistans aus Sicht der USA : Kontinuität und Wandel von 1979-2008

Afghanistan führte Eroberer selten zum Sieg, aber oft in den Ruin: Seit über zweitausend Jahren scheiterten Armeen am Hindukusch. Makedonien, Persien, Großbritannien, Russland – dies sind nur einige Nationen und Reiche, die vergeblich versuchten, sich Afghanistan untertan zu machen. Bedingt durch seine geografische Lage zwischen den östlichen Ausläufern des iranischen Plateaus und dem westlich angrenzenden Himalajagebirge wurde die Region ein „highway of conquest“. Ziel der Besatzer war dabei nie Afghanistan selbst. Der „Torbogen“ sollte sie zum indischen Subkontinent oder den warmen Gewässern des Arabischen Meeres und des Persischen Golfs führen. Der 11. September 2001 rückte Afghanistan neuerlich in den Fokus des weltweiten medialen Interesses. Nach den Anschlägen auf das World Trade Center geriet das Land als Rückzugsraum der Terrororganisation Al-Qaida in den Mittelpunkt US-amerikanischer Außenpolitik. Die Taliban weigerten sich, den Drahtzieher der Anschläge, Osama Bin Laden, auszuliefern. Als Antwort darauf rückte erneut eine Armee an den Hindukusch aus – diesmal kam sie aus den USA. Die vorliegende Arbeit hat ein doppeltes Ziel: Erstens soll sie durch eine zeithistorisch gegliederte analytische Gesamtdarstellung die geostrategischen Bedeutung Afghanistans für die USA von 1979 bis 2008 nachzeichnen. Zweitens soll anhand dieser Analyse ein geostrategisches Paradoxon Afghanistans gelöst werden: Wie kann es sein, dass ein Land, das als „Torbogen“ von sich selbst aus keine Relevanz für äußere Mächte hatte (wie sich z.B. in den 1990er Jahren zeigte ), doch immer wieder in den Mittelpunkt der Weltgeschichte – und nach 1979 der US-Außenpolitik – rückte? Dabei liegt der Arbeit die These zugrunde, dass Afghanistan erst wenn es durch eine veränderte Raum-Mächte-Konstellation geopolitisch aufgeladen wurde, eine geostrategische Relevanz für die USA erlangte. Geriet es nicht aufgrund äußerer Umstände, wie z.B. dem Einmarsch sowjetischer Truppe 1979, in den außenpolitischen Fokus Washingtons, blieb es eine „negative Einflusszone“. Das Land selbst bot historisch gesehen niemals einen (intrinsischen) geostrategischen Anreiz für eine äußere Macht, sich dort zu engagieren

Evolution of Static Allometry and Constraint on Evolutionary Allometry in a Fossil Stickleback

Allometric scaling describes the relationship of trait size to body size within and among taxa. The slope of the population-level regression of trait size against body size (i.e. static allometry) is typically invariant among closely related populations and species. Such invariance is commonly interpreted to reflect a combination of developmental and selective constraints that delimit a phenotypic space into which evolution could proceed most easily. Thus, understanding how allometric relationships do eventually evolve is important to understanding phenotypic diversification. In a lineage of fossil Threespine Stickleback (Gasterosteus doryssus), we investigated the evolvability of static allometric slopes for nine traits (five armour and four non-armour) that evolved significant trait differences across 10 samples over 8500 years. The armour traits showed weak static allometric relationships and a mismatch between those slopes and observed evolution. This suggests that observed evolution in these traits was not constrained by relationships with body size, perhaps because prior, repeated adaptation to freshwater habitats by Threespine Stickleback had generated strong selection to break constraint. In contrast, for non-armour traits, we found stronger allometric relationships. Those allometric slopes did evolve on short time scales. However, those changes were small and fluctuating and the slopes remained strong predictors of the evolutionary trajectory of trait means over time (i.e. evolutionary allometry), supporting the hypothesis of allometry as constraint