Superradiance-like Electron Transport through a Quantum Dot

We theoretically show that intriguing features of coherent many-body physics can be observed in electron transport through a quantum dot (QD). We first derive a master equation based framework for electron transport in the Coulomb-blockade regime which includes hyperfine (HF) interaction with the nuclear spin ensemble in the QD. This general tool is then used to study the leakage current through a single QD in a transport setting. We find that, for an initially polarized nuclear system, the proposed setup leads to a strong current peak, in close analogy with superradiant emission of photons from atomic ensembles. This effect could be observed with realistic experimental parameters and would provide clear evidence of coherent HF dynamics of nuclear spin ensembles in QDs.Comment: 21 pages, 10 figure

Hydraulic Approach for Dimensioning Fish Way Attraction Flow

The German Federal Institute of Hydrology (BfG) and the German Federal Waterways Engineering and Research Institute (BAW) are working to restore upstream connectivity for fish on German Federal Waterways by means of fish ways. In order for fish to find the entrance of a fish way, sufficient attraction flow is necessary. However, to this day, there is no generally accepted definition of sufficient attraction flow and how to evaluate it. Furthermore, according to the European Water Framework Directive fish of all species and sizes have to be considered for upstream migration. Thus, requirements for attraction flow are diverse. Theoretically, attraction flow should be designed as large as possible. Practically, space for fish ways is often limited and large supply structures may lead to other restrictions, especially distract fish from their passage. In addition, in terms of operational discharge, fish ways often compete with hydropower and other interests. Thus attraction flow should be designed as large as necessary and as small as possible. It is common to design attraction flow rate as a proportion of competing flow, e.g. mean annual discharge or hydro power plant design discharge. However, these approaches do not consider site specific parameters such as geometric and hydraulic boundary conditions. The framework presented characterizes requirements for attraction flow by a simple set of variables. Hydraulic jet theory is used in order to estimate attraction flow diffusion and to take into account tailrace characteristics. In doing so, site specifics such as water depths, river bed boundaries and influence of competing flow are considered. The straight forward approach aims at applicable dimensioning recommendations for attraction flow rates and fish way entrance design

Studies on the human cytomegalovirus kinase−cyclin interaction that determines host regulation and viral replication efficiency

The human cytomegalovirus (HCMV) is a significant opportunistic human pathogen that relies on a complex network of virus–host interaction. The viral protein kinase pUL97 represents a crucial determinant of replication efficiency since it acts as a viral cyclin-dependent kinase (vCDK) ortholog by combining structural and functional features of host CDKs. Importantly, vCDK/pUL97 has been found to interact with cyclin types T1, H, and B1. Two primary regions in pUL97 mediate the interaction with cyclins: interface 1 (IF1), a large contact region in the C-terminal kinase domain that overlaps with drug resistance mutation sites (amino acids 328-651), and interface 2 (IF2), a short linear binding motif within the unstructured N-terminus (231-280). IF2 is required for both pUL97 oligomerization and specific cyclin interactions, whereas IF1 contributes to cyclin binding in general. The aim of this thesis was to determine the functional relevance of the pUL97–cyclin interaction. Accordingly, the impact of clinically relevant UL97 drug-resistance mutations in the IF1 region was examined. Notably, cyclin interaction was found conserved in all analyzed mutants and viral replication fitness was almost indistinguishable from wildtype (WT), indicating a selection pressure preserving this regulatory interaction. Subsequently, partial and complete HCMV UL97 IF2 deletion mutants were generated. While smaller deletions maintained WT-like functional qualities, a complete IF2 deletion resulted in a loss of interaction with cyclins T1 and H (but not B1) as well as severely impaired replication efficiency. Furthermore, pUL97 kinase activity was significantly reduced, thus proving the functional importance of the pUL97–cyclin interaction. Importantly in this regard, knock-out and knock-down experiments confirmed the importance of cyclin H as a major determinant of HCMV replication efficiency, whereas cyclins B1 and T1 showed no impact on HCMV replication phenotype or pUL97 kinase activity. Moreover, a novel assay was established to quantify pUL97 kinase activity, thereby showing a significant increase of pUL97 kinase activity in the presence of cyclin H. The importance of cyclin H could be further highlighted by its strong upregulation upon HCMV infection, regardless of strain and cell type. Analysis of the total transcriptome indicated that the interaction between pUL97, cyclin H, and CDK7 regulates the transcription of numerous genes. Substantiating this regulatory interplay, bioinformatic analysis confirmed our protein-biochemical data on a potential ternary complex consisting of pUL97, cyclin H, and CDK7. As a central point, human CDK7 activity was increased by a pUL97-mediated trans-stimulation (while, vice versa, CDK7 did not trans-stimulate pUL97). A phospho-specific analysis indicated that the CDK7 T¬¬ loop may be phosphorylated by pUL97 during HCMV infection, indicating a so far undiscovered aspect of HCMV-specific transcriptional regulation. As a consequence of these investigations, a first covalently binding compound that inhibited the pUL97–cyclin H interaction was identified with potent anti-HCMV activity, pointing towards a novel antiviral targeting strategy. In conclusion, this thesis provides multilayered points of evidence for the functional importance of the pUL97–cyclin interaction and suggests future options for antiviral interference

Nuclear Spin Dynamics in Double Quantum Dots: Multi-Stability, Dynamical Polarization, Criticality and Entanglement

We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically-defined double quantum dot (DQD) in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.Comment: 35 pages, 19 figures. This article provides the full analysis of a scheme proposed in Phys. Rev. Lett. 111, 246802 (2013). v2: version as publishe

Solid-state magnetic traps and lattices

We propose and analyze magnetic traps and lattices for electrons in semiconductors. We provide a general theoretical framework and show that thermally stable traps can be generated by magnetically driving the particle's internal spin transition, akin to optical dipole traps for ultra-cold atoms. Next we discuss in detail periodic arrays of magnetic traps, i.e. magnetic lattices, as a platform for quantum simulation of exotic Hubbard models, with lattice parameters that can be tuned in real time. Our scheme can be readily implemented in state-of-the-art experiments, as we particularize for two specific setups, one based on a superconducting circuit and another one based on surface acoustic waves.Comment: 18 pages, 8 figure