Symmetry protected exceptional points of interacting fermions

Non-Hermitian quantum systems can exhibit spectral degeneracies known as exceptional points, where two or more eigenvectors coalesce, leading to a nondiagonalizable Jordan block. It is known that symmetries can enhance the abundance of exceptional points in noninteracting systems. Here we investigate the fate of such symmetry protected exceptional points in the presence of a symmetry preserving interaction between fermions and find that (i) exceptional points are stable in the presence of the interaction. Their propagation through the parameter space leads to the formation of characteristic exceptional "fans." In addition, (ii) we identify a new source for exceptional points which are only present due to the interaction. These points emerge from diagonalizable degeneracies in the noninteracting case. Beyond their creation and stability, (iii) we also find that exceptional points can annihilate each other if they meet in parameter space with compatible many-body states forming a third order exceptional point at the endpoint. These phenomena are well captured by an "exceptional perturbation theory" starting from a noninteracting Hamiltonian

Tunable quantum spin Hall effect in double quantum wells

The field of topological insulators (TIs) is rapidly growing. Concerning possible applications, the search for materials with an easily controllable TI phase is a key issue. The quantum spin Hall effect, characterized by a single pair of helical edge modes protected by time-reversal symmetry, has been demonstrated in HgTe-based quantum wells (QWs) with an inverted bandgap. We analyze the topological properties of a generically coupled HgTe-based double QW (DQW) and show how in such a system a TI phase can be driven by an inter-layer bias voltage, even when the individual layers are non-inverted. We argue, that this system allows for similar (layer-)pseudospin based physics as in bilayer graphene but with the crucial absence of a valley degeneracy.Comment: 9 pages, 8 figures, extended version (accepted Phys. Rev. B

An integrated SDN architecture for application driven networking

The target of our effort is the definition of a dynamic network architecture meeting the requirements of applications competing for reliable high performance network resources. These applications have different requirements regarding reli- ability, bandwidth, latency, predictability, quality, reliable lead time and allocatability. At a designated instance in time a virtual network has to be defined automatically for a limited period of time, based on an existing physical network infrastructure, which implements the requirements of an application. We suggest an integrated Software Defined Network (SDN) architecture providing highly customizable functionalities required for efficient data transfer. It consists of a service interface towards the application and an open network interface towards the physical infrastruc- ture. Control and forwarding plane are separated for better scalability. This type of architecture allows to negotiate the reser- vation of network resources involving multiple applications with different requirement profiles within multi-domain environments

A higher-resolution version of the Max Planck Institute Earth System Model (MPI-ESM1.2-HR)

The MPI‐ESM1.2 is the latest version of the Max Planck Institute Earth System Model and is the baseline for the Coupled Model Intercomparison Project Phase 6 and current seasonal and decadal climate predictions. This paper evaluates a coupled higher‐resolution version (MPI‐ESM1.2‐HR) in comparison with its lower‐resolved version (MPI‐ESM1.2‐LR). We focus on basic oceanic and atmospheric mean states and selected modes of variability, the El Niño/Southern Oscillation and the North Atlantic Oscillation. The increase in atmospheric resolution in MPI‐ESM1.2‐HR reduces the biases of upper‐level zonal wind and atmospheric jet stream position in the northern extratropics. This results in a decrease of the storm track bias over the northern North Atlantic, for both winter and summer season. The blocking frequency over the European region is improved in summer, and North Atlantic Oscillation and related storm track variations improve in winter. Stable Atlantic meridional overturning circulations are found with magnitudes of ~16 Sv for MPI‐ESM1.2‐HR and ~20 Sv for MPI‐ESM1.2‐LR at 26°N. A strong sea surface temperature bias of ~5°C along with a too zonal North Atlantic current is present in both versions. The sea surface temperature bias in the eastern tropical Atlantic is reduced by ~1°C due to higher‐resolved orography in MPI‐ESM‐HR, and the region of the cold‐tongue bias is reduced in the tropical Pacific. MPI‐ESM1.2‐HR has a well‐balanced radiation budget and its climate sensitivity is explicitly tuned to 3 K. Although the obtained reductions in long‐standing biases are modest, the improvements in atmospheric dynamics make this model well suited for prediction and impact studies

Engineering and manipulating topological qubits in 1D quantum wires

We investigate the Josephson effect in TNT and NTN junctions, consisting of topological (T) and normal (N) phases of semiconductor-superconductor 1D heterostructures in the presence of a Zeeman field. A key feature of our setup is that, in addition to the variation of the phase of the superconducting order parameter, we allow the orientation of the magnetic field to change along the junction. We find a novel magnetic contribution to the Majorana Josephson coupling that permits the Josephson current to be tuned by changing the orientation of the magnetic field along the junction. We also predict that a spin current can be generated by a finite superconducting phase difference, rendering these materials potential candidates for spintronic applications. Finally, this new type of coupling not only constitutes a unique fingerprint for the existence of Majorana bound states but also provides an alternative pathway for manipulating and braiding topological qubits in networks of wires.Comment: references and a note were added in v2; 6 pages, 2 figures; v1 had been submitted for the ICM2012 proceedings on the 31st of May 201

How Can Grid Technologies Help in Earth System Sciences?

Earth System Modelling strongly relies on a wide data base: Data serve as input in models and the model results have to been compared with other models or observational data. Unfortunately, the existing data are distributed over many archives and databases and vary highly in quality, available description (metadata), and accessibility. This encumbers collaborative work of scientists and makes routine workflows often tedious.The implemented infrastructure provides tools for effective data discovery and data transfer. A central catalogue of discovery metadata enables the user to seek after data in all connected data archives. The user can specify regional and time constraints, variable names and experiment labels for his data query. The provider specific implementation of the data access as well as of the data preparation is hidden behind a common WSDL defined web service interface. Thus the user has transparent and uniform access to all data archives within C3Grid

OSS in Climate Modelling, Introducing a Software Policy at an MPI

The Climate Model „ICON“ has been developed at MPI for Meteorology for climate and weather research. The model consist of approx. 500 k lines of (much legacy) code developed by 100s of people across the world and is under constant change due to porting to the most modern HPC architectures. Code owner are 4 institutions: MPI-M, DWD, KIT and DKRZ These institutions had been developing the code on the legal basis of cooperation agreements. A license specifically drafted by a law firm as “open-source-like”, has not proven useful . Among the problems with this license were the facts that it has not been accepted by many journals, and put up too high hurdles for the community of climate scientists to pick up the code easily and modify it for their use cases: Proliferation of the code into the community was unsatisfyingly low. After these experiences the idea was accepted, that licensing the code as open source software would solve many of such problems. The selection of the most appropriate form of OSL rose quite some discussion amongst the parties involved: We opted for the permissive BSD. We drafted two documents, a software policy and a contributors license agreement that would enable MPI-M to license all their software development and especially “their” parts of ICON as Open Source software, under the BSD-3-Clause license. We are hoping to promote the development and use of ICON worldwide, enabling researchers changing institution during their career to be able to continue to use “their” work, taking away the pain of thinking about how to license from researchers, establishing a fair way of sharing IP rights between MPG and the individual coder . In our presentation we will try to shortly explain the legal background and the legal meanings of both documents, describe the process it took to implement these documents at the institute (Directors board, Betriebsrat, etc.) and illuminate which IT- and personal infrastructure is needed for the policy to work