Recent progress in open quantum systems: Non-Gaussian noise and decoherence in fermionic systems

We review our recent contributions to two topics that have become of interest in the field of open, dissipative quantum systems: non-Gaussian noise and decoherence in fermionic systems. Decoherence by non-Gaussian noise, i.e. by an environment that cannot be approximated as a bath of harmonic oscillators, is important in nanostructures (e.g. qubits) where there might be strong coupling to a small number of fluctuators. We first revisit the pedagogical example of dephasing by classical telegraph noise. Then we address two models where the quantum nature of the noise becomes essential: "quantum telegraph noise" and dephasing by electronic shot noise. In fermionic systems, many-body aspects and the Pauli principle have to be taken care of when describing the loss of phase coherence. This is relevant in electronic quantum transport through metallic and semiconducting structures. Specifically, we recount our recent results regarding dephasing in a chiral interacting electron liquid, as it is realized in the electronic Mach-Zehnder interferometer. This model can be solved employing the technique of bosonization as well as a physically transparent semiclassical method.Comment: Proceedings of Ustron 2008 conference, 6 pages, 3 figure

Efficient on-chip source of microwave photon pairs in superconducting circuit QED

We describe a scheme for the efficient generation of microwave photon pairs by parametric downconversion in a superconducting transmission line resonator coupled to a Cooper pair box serving as an artificial atom. By properly tuning the first three levels with respect to the cavity modes, the down-conversion probability may become higher than in the most efficient schemes for optical photons. We show this by numerically simulating the dissipative quantum dynamics of the coupled cavity-box system and discuss the effects of dephasing and relaxation. The setup analyzed here might form the basis for a future on-chip source of entangled microwave photons.Comment: 5 pages, 5 figure

Accurate Prediction of Core Properties for Chiral Molecules using Pseudo Potentials

Pseudo potentials (PPs) constitute perhaps the most common way to treat relativity, often in a formally non-relativistic framework, and reduce the electronic structure to the chemically relevant part. The drawback is that orbitals obtained in this picture (called pseudo orbitals (POs)) show a reduced nodal structure and altered amplitude in the vicinity of the nucleus, when compared to the corresponding molecular orbitals (MOs). Thus expectation values of operators localized in the spatial core region that are calculated with POs, deviate significantly from the same expectation values calculated with all-electron (AE) MOs. This study describes the reconstruction of AE MOs from POs, with a focus on POs generated by energy consistent pseudo Hamiltonians. The method reintroduces the nodal structure into the POs, thus providing an inexpensive and easily implementable method that allows to use nonrelativistic, efficiently calculated POs for good estimates of expectation values of core-like properties. The discussion of the method proceeds in two parts: Firstly, the reconstruction scheme is developed for atomic cases. Secondly, the scheme is discussed in the context of MO reconstruction and successfully applied to numerous numerical examples. Starting from the equations of the state-averaged multi-configuration self- consistent field method, used for the generation of energy consistent pseudo potentials, the electronic spectrum of the many-electron Hamiltonian is linked to the spectrum of the effective one-electron Fock operator by means of various models systems. This relation and the Topp–Hopfield–Kramers theorem, are used to show the shape-consistency of energy-consistent POs for atomic systems. Shape-consistency describes POs that follow distinct AOs exactly outside a core-radius r_core . In the cases presented here, shape-consistency holds to a high degree and it follows that in atomic systems every PO has one distinct partner in the set of AOs. The overlap integral between these two orbitals is close to one, as it is determined mainly by the spatial orbital parts outside r_core . Expanding, e.g., a 5s PO in occupied AOs, the 5s AOs will have the highest contribution. The POs itself contains contributions from high-energy unoccupied AOs as well (e.g. 15s), which damp the nodal structure of the POs near the nucleus. Consequently, neglecting contributions from unoccupied orbitals in a projection of the POs reintroduces the nodal structure. This approach is not directly suitable for the reconstruction of MOs, as they often need to be expanded in a full set of AOs at each atomic center, including all unoccupied orbitals, to properly account for the electron density distribution in the molecule. However, it is shown that the occupied MOs are well described by occupied and low-energy unoccupied AOs only and a mapping of the POs onto a basis containing only these orbitals reconstructs the nodal structure of the MO. The approach uses only standard integrals available in most quantum chemistry programs. The computational cost of these integrals scales with N^2 , where N is the number of basis functions. The most time consuming step is a Gram-Schmidt orthogonalization, which scales in this implementation with MN^2 , M being the number of reconstructed orbitals. The reconstruction method is subsequently tested: Valence orbitals of atomic, closed-shell systems were reconstructed numerically exactly. The influence of numerical parameters is investigated using the molecule BaF . It is shown that the method is basis set dependent: One has to ensure that the PO basis can be expanded exactly in the basis of AOs. Violating this rule of thumb may degrade the quality of reconstructed orbitals. Additionally, the representation of MOs by a linear combination of occupied and unoccupied AOs is investigated. For the exemplary systems, the shells included in the fitting procedure of the PP were sufficient. Reconstruction of the alkaline earth monofluorides showed that periodic trends can be reconstructed as well. Scaling of hyperfine structure parameters with increasing atomic number is discussed. For hydrogenic atoms, the scaling should be linear, whereas small deviations from the linear behavior were observed for molecules. The scaling laws computed from reconstructed and reference orbitals were almost identical. In this context, the failure of commonly used relativistic enhancement factors beyond atomic number 100 is discussed. Applicability of the method is also tested on parity violating properties for which the main contribution is generated by the valence orbitals near the nucleus. Symmetry-independence of the method is shown by successful reconstruction of orbitals of the tetrahedral PbCl_4 and chiral NWHClF. The reliable reconstruction of chemical trends is shown with the help of the NWHClF derivatives NWHBrF and NWHFI. The study of chiral compounds as, e.g., NWHClF and its group 17 derivatives, which have been proposed as paradigm for the detection of parity-violation in chiral molecules, remains of great importance. Especially the direct determination of absolute configuration of chiral centers is still non-trivial. The author contributed to this field with a self-written molecular dynamics (MD) program to simulate Coulomb explosions and thus to provide an insight especially into the early explosion stages directly after an instantaneous multi-ionization of the molecule CHBrClF, comparable to experiments using the Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) technique. An algorithm for the determination of the investigated molecule’s absolute configuration from time-of-flight data and detection locations of molecular fragments is included in the program. The program was used to generate experiment-equivalent data which allowed for the first time the investigation of non-racemic mixtures by the analysis routines of the experiment. The MD program includes harmonic and anharmonic bond potentials. A charge-exchange model can model partial charges in early phases of the Coulomb explosion. Furthermore, Born–Oppenheimer MD simulations and statistical models are used to explain the relative abundance of products belonging to competing reaction channels, as obtained by photoion coincidence measurements. Additionally, qualitative statements about reaction branching ratios are made by comparing the partition functions of involved degrees of freedom. Analytic equations for partition functions of simple models are used to provide a simple formula allowing fast estimates of reaction branching ratios

Putrid Pistols EP

Prose by Carissa Marquardt

Optomechanical position detection enhanced by de-amplification using intracavity squeezing

It has been predicted and experimentally demonstrated that by injecting squeezed light into an optomechanical device it is possible to enhance the precision of a position measurement. Here, we present a fundamentally different approach where the squeezing is created directly inside the cavity by a nonlinear medium. Counterintuitively, the enhancement of the signal to noise ratio works by de-amplifying precisely the quadrature that is sensitive to the mechanical motion without losing quantum information. This enhancement works for systems with a weak optomechanical coupling and/or strong mechanical damping. This could allow for larger mechanical bandwidth of quantum limited detectors based on optomechanical devices. Our approach can be straightforwardly extended to Quantum Non Demolition (QND) qubit detection.Comment: references added, slight change

Rural networks in the funding period 2007 - 2013: A critical review of the EU policy instrument

Rural Networks have been implemented as an instrument to enhance EU rural development policies in the funding period 2007-2013. Gaps in European programme documents concerning the networks' purpose and their evaluation led to a survey of the National Network Units being conducted in 2010. Besides investigating how these gaps are bridged nationally, the survey aimed to provide an overview of the development of the networks, of the initial experiences and challenges faced in running the networks, and to assess their potential impact. Empirical findings show that the networks probably support rural development (policies) and create added value. However, ways of demonstrating this impact in quantitative terms are lacking. Member states tend to stick closely to the specifications provided by the Commission and rarely go beyond them even if they are inadequate - even though this is legally possible. As a result, one purpose originally envisaged for the networks, namely to contribute to improving governance, is neglected. The paper provides proposals for modifying EC Regulations so as to enhance rural networks' impact and points to the need for further theoretical research corroborating the networks' value and increasing their effectiveness. -- Für die Förderperiode 2007-2013 wurden Netze für den Ländlichen Raum als Politikinstrument zur Aufwertung der EU Politik zur ländlichen Entwicklung aufgebaut. Unzulänglichkeiten in den EU Programmdokumenten im Hinblick auf die Zweckbestimmung und die Evaluierung der Netze gaben Anlass, im Jahr 2010 eine Umfrage unter den Nationalen Vernetzungsstellen durchzuführen. Es sollte einerseits der Frage nachgegangen werden, wie auf nationaler Ebene mit den regulatorischen Lücken umgegangen wird, andererseits zielte die Umfrage darauf ab, die Entwicklung der Netze zu erfassen, sowie erste Erfahrungen und Herausforderungen im Bezug auf das Management der Netze und ihre potentiellen Auswirkungen auszumachen. Die empirischen Ergebnisse zeigen, dass die Netze wahrscheinlich die Umsetzung ländlicher Entwicklung(spolitik) unterstützen und einen Mehrwert hervorbringen. Allerdings fehlt es an Mitteln, diese Wirkungen quantitativ nachzuweisen. Ferner, da die Mitgliedstaaten dazu tendieren, sich stark an den EU Vorgaben zu orientieren und nicht über diese hinauszugehen, auch wenn sie unzureichend sind, wird das ursprünglich für die Netze vorgesehene Ziel, einen Beitrag zur Verbesserung von Governance zu leisten, allseits vernachlässigt. In dem Papier werden Vorschläge für mögliche Modifizierungen der EU Verordnungen gemacht, die die positive Wirkung der Netze verstärken könnten. Außerdem wird der Bedarf an netzwerktheoretischer Forschung zur Unterlegung des Werts der Netze für den Ländlichen Raum und zur Vergrößerung ihrer Effektivität herausgestellt.National Rural Networks,Policy Instrument,Rural Development,CAP,Netze für den Ländlichen Raum,Politikinstrument,Ländliche Entwicklung,GAP

Galactic cosmic ray hydrogen spectra and radial gradients in the inner heliosphere measured by the HELIOS Experiment 6

Context: The HELIOS solar observation probes provide unique data regarding their orbit and operation time. One of the onboard instruments, the Experiment 6 (E6), is capable of measuring ions from 4 to several hundred MeV/nuc. Aims: In this paper we aim to demonstrate the relevance of the E6 data for the calculation of galactic cosmic ray (GCR), anomolous cosmic ray (ACR), and solar energetic particle (SEP) fluxes for different distances from the sun and time periods. Methods: Several corrections have been applied to the raw data: determination of the Quenching factor of the scintillator, correction of the temperature dependent electronics, degradation of the scintillator as well as the effects on the edge of semi-conductor detectors. Results: Fluxes measured by the E6 are in accordance with the force field solution for the GCR and match models of the anomalous cosmic ray propagation. GCR radial gradients in the inner heliosphere show a different behaviour than in the outer heliosphereComment: 8 pages, 10 figure