Stroboscopic observation of quantum many-body dynamics

Recent experiments have demonstrated single-site resolved observation of cold atoms in optical lattices. Thus, in the future it may be possible to take repeated snapshots of an interacting quantum many-body system during the course of its evolution. Here we address the impact of the resulting quantum (anti-)Zeno physics on the many-body dynamics. We use the time-dependent density-matrix renormalization group to obtain the time evolution of the full wave function, which is then periodically projected in order to simulate realizations of stroboscopic measurements. For the example of a one-dimensional lattice of spinless fermions with nearest-neighbor interactions, we find regimes for which many-particle configurations are stabilized or destabilized, depending on the interaction strength and the time between observations

PubPharm - Der Fachinformationsdienst Pharmazie

Der Fachinformationsdienst (FID) Pharmazie verfolgt das Ziel, die Informationsinfrastruktur und die Literaturversorgung für die pharmazeutische Hochschulforschung nachhaltig zu verbessern. Das Projekt wird seit dem 1. Januar 2015 von der Deutschen Forschungsgemeinschaft gefördert. Eine Besonderheit stellt die Kooperation zwischen der Universitätsbibliothek Braunschweig und dem Institut für Informationssysteme (IfIS) der TU Braunschweig dar, wodurch aktuelle Forschung auf dem Gebiet der Informatik in die Implementierung innovativer FID-Dienste mündet. Im Zentrum des Projektes steht der nutzerzentrierte Aufbau einer erweiterbaren und personalisierbaren Informationsinfrastruktur. Das vom FID entwickelte Discovery System „PubPharm“ zur pharmaziespezifischen Recherche basiert, als Weiterentwicklung des beluga-Systems der SUB Hamburg, auf der Open Source Software VuFind. Als Datengrundlage enthält es u.a. die Medline Daten, erweitert durch Normdaten, die unter anderem die Suche nach chemischen Strukturen erlauben. Gleichzeitig werden vom Institut für Informationssysteme innovative Suchmöglichkeiten basierend auf Narrativer Intelligenz untersucht und perspektivisch in das Retrieval des Discovery Systems eingebunden. Im Rahmen von sog. FID-Lizenzen bietet der FID Pharmazie Wissenschaftlern/innen Volltextzugriff auf pharmazeutische Fachzeitschriften. Bestandteil der Lizenzen ist das Recht zur Langzeitarchivierung. Bei deren technischer Umsetzung kooperiert der FID mit der TIB Hannover. Der FID Pharmazie koppelt seine Aktivitäten eng an die pharmazeutische Fachcommunity: unter anderem begleitet ein Fachbeirat die Entwicklungen. Im Rahmen der Öffentlichkeitsarbeit werden Nutzer/innen umfassend über die Angebote informiert, u.a. in Webcasts und im PubPharm Blog.The Specialised Information Service (SIS) Pharmacy aims at sustainably improving the information infrastructure and the supply of literature for academic pharmaceutical research in Germany. The project is being funded by the German Research Foundation since January 1st 2015. A special feature of the project is the collaboration between Braunschweig University Library and the Institute for Information Systems (IfIS) at Braunschweig University, through which cutting edge informatics research is being incorporated into SIS services. A core aspect is the user-centric implementation of an extensible and customizable information infrastructure. The “PubPharm” discovery system, developed by SIS Pharmacy for pharmacy-specific literature search, is an extension of the beluga-System (SUB Hamburg) which is based on the open source software VuFind. Its database comprises, amongst other sources, Medline data, and also authority data which enables specialised searches, e.g. for chemical structures. At the same time the IfIS is evaluating innovative search functions which, if proving to be beneficial, will be incorporated into the retrieval mechanisms of the discovery system. Within the scope of the SIS licenses, full text access to pharmaceutical journals is being provided to scientists. Part of the licenses is the right to long-term preservation. For technical implementation SIS Pharmacy is cooperating with the TIB Hanover. SIS Pharmacy liaises closely with the pharmaceutical research community, e.g. an advisory board is involved in steering the development of services. As part of public relations, users are being comprehensively informed, e.g. by web casts and the PubPharm blog

Far-from-equilibrium quantum many-body dynamics

The theory of real-time quantum many-body dynamics as put forward in Ref. [arXiv:0710.4627] is evaluated in detail. The formulation is based on a generating functional of correlation functions where the Keldysh contour is closed at a given time. Extending the Keldysh contour from this time to a later time leads to a dynamic flow of the generating functional. This flow describes the dynamics of the system and has an explicit causal structure. In the present work it is evaluated within a vertex expansion of the effective action leading to time evolution equations for Green functions. These equations are applicable for strongly interacting systems as well as for studying the late-time behaviour of nonequilibrium time evolution. For the specific case of a bosonic N-component phi^4 theory with contact interactions an s-channel truncation is identified to yield equations identical to those derived from the 2PI effective action in next-to-leading order of a 1/N expansion. The presented approach allows to directly obtain non-perturbative dynamic equations beyond the widely used 2PI approximations.Comment: 20 pp., 6 figs; submitted version with added references and typos corrected

Morphology formation in binary mixtures upon gradual destabilisation

Spontaneous liquid-liquid phase separation is commonly understood in terms of phenomenological mean-field theories. These theories correctly predict the structural features of the fluid at sufficiently long time scales and wavelengths. However, these conditions are not met in various examples in biology and materials science where the mixture is slowly destabilised, and phase separation is strongly affected by critical thermal fluctuations. We propose a mechanism of pretransitional structuring of a mixture that approaches the miscibility gap and predict scaling relations that describe how the characteristic feature size of the emerging morphology decreases with an increasing quench rate. These predictions quantitatively agree with our kinetic Monte Carlo and molecular dynamics simulations of a phase-separating binary mixture, as well as with previously reported experimental observations. We discuss how these predictions are affected by non-conserved order parameters (e.g., due to chemical reactions or alignment of liquid-crystalline molecules), hydrodynamics and active transport

Ultrakalte Atome in optischen Gittern: Vielteilchendynamik im Quantenregime

Ultracold atoms can be trapped in periodic intensity patterns of light created by counterpropagating laser beams, so-called optical lattices. In contrast to its natural counterpart, electrons in a solid state crystal, this man-made setup is very clean and highly isolated from environmental degrees of freedom. Moreover, to a large extent, the experimenter has dynamical control over the relevant system parameters: the interaction between atoms, the tunneling amplitude between lattice sites, and even the dimensionality of the lattice. These advantages render this system a unique platform for the simulation of quantum many-body dynamics for various lattice Hamiltonians as has been demonstrated in several experiments by now. The most significant step in recent times has arguably been the introduction of single-site detection of individual atoms in optical lattices. This technique, based on fluorescence microscopy, opens a new doorway for the study of quantum many-body states: the detection of the microscopic atom configuration. In this thesis, we theoretically explore the dynamics of ultracold atoms in optical lattices for various setups realized in present-day experiments. Our main focus lies on aspects that become experimentally accessible by (realistic extensions of) the novel single-site measurement technique. The first part deals with the expansion of initially confined atoms in a homogeneous lattice, which is one way to create atomic motion in experiments. We analyze the buildup of spatial correlations during the expansion of a finitely extended band insulating state in one dimension. The numerical simulation reveals the creation of remote spin-entangled fermions in the strongly interacting regime. We discuss the experimental observation of such spin-entangled pairs by means of a single-site measurement. Furthermore, we suggest studying the impact of observations on the expansion dynamics for the extreme case of a projective measurement in the spatial occupation number basis realized by a single-site detection. The analysis of the resulting quantum Zeno physics shows regimes for which the initial many-particle configurations are stabilized or destabilized, depending on the observation time interval and the interaction strength. In the second part, the measurement of the local current operator in an optical lattice is discussed. We propose a measurement protocol that combines single-site detection with already existing optical superlattices. The measurement outcomes can even be used to calculate spatial current-current correlations since the local currents are simultaneously measured at various positions. We illustrate the prospects of this new sensing method by a numerical study of the current statistics for interacting bosons in one and two dimensions. In the latter case, we discuss how the on-site interactions affect the equilibrium currents of bosons in an artificial magnetic field. We substantiate the feasibility of the protocol by considering possible error sources, restrictions in currently used single-site detection, and its applicability in experimental setups used to create artificial gauge fields.Ultrakalte Atome lassen sich in periodischen Intensitätsmustern, welche durch entgegenlaufende Laserstrahlen erzeugt werden, fangen. Diese werden optische Gitter genannt. Im Gegensatz zu ihrem natürlichen Gegenstück, Elektronen in Festkörpern, ist das System äußerst rein und lässt sich sehr gut von der Umgebung abschirmen. Zudem hat der Experimentator in großem Umfang dynamische Kontrolle über die relevanten Größen des Systems: die Wechselwirkung zwischen den Atomen, das Tunnelmatrixelement zwischen Gitterplätzen und sogar die Dimension des Gitters. Diese Eigenschaften machen ultrakalte Atome in optischen Gittern zu einer einzigartigen Plattform um die Quantendynamik von Vielteilchensystemen in verschiedenen Gittermodellen zu studieren. Die wohl bedeutendste Entwicklung in jüngster Vergangenheit ist die Detektion einzelner Atome auf einzelnen Gitterplätzen des optischen Gitters. Diese auf der Fluoreszenzmikroskopie beruhende Methode eröffnet einen völlig neuen Zugang zur Untersuchung von quantenmechanischen Vielteilchenzuständen: Die Messung der mikroskopischen Verteilung der Atome. Diese Dissertation widmet sich der theoretischen Untersuchung der Quantendynamik ultrakalter Atome in optischen Gittern für verschiedene Modelle, die zurzeit in Experimenten simuliert werden können. Unser Hauptaugenmerk liegt dabei auf Eigenschaften, welche mittels der neuartigen hochaufgelösten Fluoreszenzabbildung einzelner Atome experimentell beobachtet werden können. Der erste Abschnitt der Arbeit betrachtet die Expansion von zunächst räumlich eingeschränkten Atomen in einem homogenen optischen Gitter. Während in bisherigen Experimenten die Zeitentwicklung des Dichteprofils studiert wurde, analysieren wir die Herausbildung von räumlichen Korrelationen während der Expansion eines endlich ausgedehnten Bandisolators in einer Dimension. Insbesondere zeigen die numerischen Simulationen, dass eine starke lokale Wechselwirkung zur Erzeugung von Spin-verschränkten Fermionenpaaren an entfernten Gitterplätzen führt. Wir beschreiben wie sich diese Spin-verschränkten Paare mit Hilfe des oben beschriebenen Messverfahrens nachweisen lassen. Zudem schlagen wir vor den Einfluss der quantenmechanischen Messung auf die Expansionsdynamik durch wiederholte Beobachtung der einzelnen Atome zu studieren. Wir simulieren diese Dynamik für den idealisierten Fall einer projektiven Messung in die räumliche Besetzungszahlbasis. Die Untersuchung der resultierende Quanten-Zeno Dynamik zeigt eine erhöhte oder verringerte Zerfallsrate der anfänglichen Vielteilchenkonfiguration, in Abhängigkeit von dem Beobachtungsintervall und der Wechselwirkungsstärke zwischen den Atomen. Der zweite Abschnitt der Arbeit widmet sich der Messung des lokalen Strom\-operators in optischen Gittern. Wir entwerfen ein Messprotokoll, welches auf einer Kombination der Detektion einzelner Atome auf einzelnen Gitterplätzen und experimentell schon eingesetzten optischen Übergittern beruht. Dieses Protokoll erlaubt die gleichzeitige Messung der lokalen Stromoperatoren an unterschiedlichen Orten, wodurch sich auch räumliche Strom-Strom Korrelationsfunktionen berechnen lassen. Wir veranschaulichen die Möglichkeiten dieser neuen Strommessung durch numerische Simulationen und diskutieren die Statistik der Eigenwerte des lokalen Stroms für wechselwirkende Bosonen in einer und zwei Dimensionen. Im letzteren Fall untersuchen wir den Einfluss der lokalen Wechselwirkung zwischen Bosonen auf deren Gleichgewichtsströme in einem künstlichen Magnetfeld. Wir belegen die experimentelle Umsetzbarkeit des Protokolls durch Berücksichtigung möglicher Fehlerquellen, von Einschränkungen in der zurzeit eingesetzten Detektion einzelner Atome, sowie seines Einsatzes in experimentellen Aufbauten zur Erzeugung künstlicher Eichfelder

TRM4: Range performance model for electro-optical imaging systems

TRM4 is a commonly used model for assessing device and range performance of electro-optical imagers. The latest version, TRM4.v2, has been released by Fraunhofer IOSB of Germany in June 2016. While its predecessor, TRM3, was developed for thermal imagers, assuming blackbody targets and backgrounds, TRM4 extends the TRM approach to assess three imager categories: imagers that exploit emitted radiation (TRM4 category Thermal), reflected radiation (TRM4 category Visible/NIR/SWIR), and both emitted and reflected radiation (TRM4 category General). Performance assessment in TRM3 and TRM4 is based on the perception of standard four-bar test patterns, whether distorted by under-sampling or not. Spatial and sampling characteristics are taken into account by the Average Modulation at Optimum Phase (AMOP), which replaces the system MTF used in previous models. The Minimum Temperature Difference Perceived (MTDP) figure of merit was introduced in TRM3 for assessing the range performance of thermal imagers. In TRM4, this concept is generalized to the MDSP (Minimum Difference Signal Perceived), which can be applied to all imager categories. In this paper, we outline and discuss the TRM approach and pinpoint differences between TRM4 and TRM3. In addition, an overview of the TRM4 software and its functionality is given. Features newly introduced in TRM4, such as atmospheric turbulence, irradiation sources, and libraries are addressed. We conclude with an outlook on future work and the new module for intensified CCD cameras that is currently under development

Simulating copolymeric nanoparticle assembly in the co-solvent method: How mixing rates control final particle sizes and morphologies

The self-assembly of copolymeric vesicles and micelles in micromixers is studied by External Potential Dynamics (EPD) simulations – a dynamic density functional approach that explicitly accounts for the polymer architecture both at the level of thermodynamics and dynamics. Specifically, we focus on the co-solvent method, where nanoparticle precipitation is triggered by mixing a poor co-solvent into a homogeneous copolymer solution in a micromixer. Experimentally, it has been reported that the flow rate in the micromixers influences the size of the resulting particles as well as their morphology: At small flow rates, vesicles dominate; with increasing flow rate, more and more micelles form, and the size of the particles decreases. Our simulation model is based on the assumption that the flow rate mainly sets the rate of mixing of solvent and co-solvent. The simulations reproduce the experimental observations at an almost quantitative level and provide insight into the underlying physical mechanisms: First, they confirm an earlier conjecture according to which the size control takes place in the earliest stage of the particle self-assembly, during the spinodal decomposition of polymers and solvent. Second, they reveal a crossover between different morphological regimes as a function of mixing rate. Hence they demonstrate that varying the mixing rate in a co-solvent setup is an effective way to control two key properties of drug delivery systems, their mean size and their morphology