Quantum Reversibility: Is there an Echo?

We study the possibility to undo the quantum mechanical evolution in a time reversal experiment. The naive expectation, as reflected in the common terminology ("Loschmidt echo"), is that maximum compensation results if the reversed dynamics extends to the same time as the forward evolution. We challenge this belief, and demonstrate that the time $t_r$ for maximum return probability is in general shorter. We find that $t_r$ depends on $lambda = eps_evol/eps_prep$, being the ratio of the error in setting the parameters (fields) for the time reversed evolution to the perturbation which is involved in the preparation process. Our results should be observable in spin-echo experiments where the dynamical irreversibility of quantum phases is measured.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let

The chief digital officer position and its firm-level impact: A literature review on CDO research and an analysis of CDO presence and performance implications

With rapidly advancing technologies and digital innovations, companies face the need to adapt to the new digital world and to digitally transform their business models. For executing the digital transformation process, more and more companies decide to entrust a new C-level manager with all challenges and complexity arising from digital transformation, the Chief Digital Officer (CDO). As the CDO position is still fairly new, research in this field is limited and requires further attention by scholars. Therefore, this study aims to address three fundamental research questions concerning the nature of the CDO position and corresponding implications not only to inform practitioners but also to enrich the scholarly discussion on CDOs. By understanding existing literature on CDOs based on a systematic literature review, this thesis answers the first research question regarding what characterizes the CDO position. Building on these insights and drawing from a comprehensive theoretical framework consisting of upper echelons theory, contingency theory, human capital theory and the resource-based view, hypotheses are developed for answering research questions two and three. While the second research question focuses on factors, which influence CDO presence within a company, the third research question addresses the impact of a CDO on company performance. Based on a large-scale sample of panel data comprised of S&P 500 companies, generalized estimating equations models, propensity score matching and fixed effects regression models are exploited in order to derive answers for both research questions two and three. As influencing factors for CDO presence, the results show that especially early tenure CEOs and CEOs of larger companies are more likely to employ a CDO. Although no evidence can be observed for positive performance implications of CDOs, also given different company contingencies, the insights of this study's analyses show that certain CDO characteristics as well as in combination with CIO presence and varying CEO characteristics are more favorable over others in terms of company performance measured by return on assets and Tobin's Q

Complexity in parametric Bose-Hubbard Hamiltonians and structural analysis of eigenstates

We consider a family of chaotic Bose-Hubbard Hamiltonians (BHH) parameterized by the coupling strength $k$ between neighboring sites. As $k$ increases the eigenstates undergo changes, reflected in the structure of the Local Density of States. We analyze these changes, both numerically and analytically, using perturbative and semiclassical methods. Although our focus is on the quantum trimer, the presented methodology is applicable for the analysis of longer lattices as well.Comment: 4 pages, 4 figure

Controlled quantum stirring of Bose-Einstein condensates

By cyclic adiabatic change of two control parameters of an optical trap one can induce a circulating current of condensed bosons. The amount of particles that are transported per period depends on the "radius" of the cycle, and this dependence can be utilized in order to probe the interatomic interactions. For strong repulsive interaction the current can be regarded as arising from a sequence of Landau-Zener crossings. For weaker interaction one observes either gradual or coherent mega crossings, while for attractive interaction the particles are glued together and behave like a classical ball. For the analysis we use the Kubo approach to quantum pumping with the associated Dirac monopoles picture of parameter space.Comment: 12 pages, 8 figure

CityScapeLab Berlin: A Research Platform for Untangling Urbanization Effects on Biodiversity

Urban biodiversity conservation requires an understanding of how urbanization modulates biodiversity patterns and the associated ecosystem services. While important advances have been made in the conceptual development of urban biodiversity research over the last decades, challenges remain in understanding the interactions between different groups of taxa and the spatiotemporal complexity of urbanization processes. The CityScapeLab Berlin is a novel experimental research platform that allows the testing of theories on how urbanization affects biodiversity patterns and biotic interactions in general and the responses of species of conservation interest in particular. We chose dry grassland patches as the backbone of the research platform because dry grasslands are common in many urban regions, extend over a wide urbanization gradient, and usually harbor diverse and self-assembled communities. Focusing on a standardized type of model ecosystem allowed the urbanization effects on biodiversity to be unraveled from effects that would otherwise be masked by habitat- and land-use effects. The CityScapeLab combines different types of spatiotemporal data on (i) various groups of taxa from different trophic levels, (ii) environmental parameters on different spatial scales, and (iii) on land-use history. This allows for the unraveling of the effects of current and historical urban conditions on urban biodiversity patterns and the related ecological functions.BMBF, 01LC1501, BIBS-Verbund: Bridging in Biodiversity Science (BIBS

Emerging Urban Forests: Opportunities for Promoting the Wild Side of the Urban Green Infrastructure

Many cities aim to increase urban forest cover to benefit residents through the provision of ecosystem services and to promote biodiversity. As a complement to traditional forest plantings, we address opportunities associated with “emerging urban forests” (i.e., spontaneously developing forests in cities) for urban biodiversity conservation. We quantified the area of successional forests and analyzed the species richness of native and alien plants and of invertebrates (carabid beetles, spiders) in emerging forests dominated by alien or native trees, including Robinia pseudoacacia, Acer platanoides, and Betula pendula. Emerging urban forests were revealed as shared habitats of native and alien species. Native species richness was not profoundly affected by the alien (co-)dominance of the canopy. Instead, native and alien plant species richnesses were positively related. Numbers of endangered plants and invertebrates did not differ between native- and alien-dominated forest patches. Patterns of tree regeneration indicate different successional trajectories for novel forest types. We conclude that these forests (i) provide habitats for native and alien species, including some endangered species, (ii) allow city dwellers to experience wild urban nature, and (iii) support arguments for adapting forests to dynamic urban environments. Integrating emerging urban forests into the urban green infrastructure is a promising pathway to sustainable cities and can complement traditional restoration or greening approaches.BMBF, 01LC1501, Bridging in Biodiversity Science (BIBS

Encounters with Southeast Asian Modernism

Against the backdrop of the Bauhaus centenary in 2019, Encounters with Southeast Asian Modernism examined the history, significance, and future of postcolonial modernism in this region, with partners in four cities – Jakarta, Phnom Penh, Singapore, and Yangon. The project provided a historical perspective on the societal and political upheaval that accompanied the transition to independence after the colonial period in these countries. It also showcased current initiatives in the fields of art, architecture, and science that are committed to the preservation and use of Modernist buildings. In 2020, the project will continue with an exhibition and accompanying program in Berlin