Non-equilibrium quantum transport coefficients and the transient dynamics of full counting statistics in the strong coupling and non-Markovian regimes

Non-equilibrium transport properties of quantum systems have recently become experimentally accessible in a number of platforms in so-called full-counting experiments that measure transient and steady state non-equilibrium transport dynamics. We show that the effect of the measurement back-action can be exploited to gain access to relevant transport coefficients. This relationship is general, but becomes most conspicuous in the transient dynamics of open quantum systems understrong coupling to non-Markovian environments. In order to explore this regime, a new simulation method for the generation of full counting statistics of non-Markovian, strong-coupling transport settings has been developed that is expressed in terms of a hierarchy of equations of motion. With this tool we gain access to the relevant regime and instantiate our proposal with the study of energetic conductance between two baths connected via a few level system.Comment: 7 pages, 3 figures; To appear in Phys. Rev.

Initial System-Environment Correlations via the Transfer Tensor Method

Open quantum systems exhibiting initial system-environment correlations are notoriously difficult to simulate. We point out that given a sufficiently long sample of the exact short-time evolution of the open system dynamics, one may employ transfer tensors for the further propagation of the reduced open system state. This approach is numerically advantageous and allows for the simulation of quantum correlation functions in hardly accessible regimes. We benchmark this approach against analytically exact solutions and exemplify it with the calculation of emission spectra of multichromophoric systems as well as for the reverse temperature estimation from simulated spectroscopic data. Finally, we employ our approach for the detection of spectral signatures of electromagnetically-induced transparency in open three-level systems.Comment: 9 pages, 7 figure

Matrix-product-state based studies of bosonic flux ladders

Flux ladders constitute the minimal setup enabling a systematic understanding of the rich physics of interacting particles subjected simultaneously to a strong magnetic field and a lattice potential. The recent realization of flux ladders in ultracold quantum gases with artificial magnetic fields has attracted great interest. In this thesis, we study various aspects of interacting bosonic flux ladders using extensive matrix-product-state based calculations. Specifically, the numerical techniques include the variational ground-state optimization by means of the density-matrix renormalization-group method, a purification approach for the study of finite-temperature states, as well as time-evolution methods for the simulation of quench dynamics. In an introductory part, we recapitulate key features and important ground-state phases of the flux-ladder model and discuss the numerical methods. Subsequently, the main results are presented as follows. First, the emphasis is put on model parameters which are envisioned to be realized in a future quantum gas experiment exploiting the internal states of potassium atoms as a synthetic dimension. Considering a particle filling of one boson per rung, we map out the ground-state phase diagram and report on a Mott-insulating Meissner phase as well as on biased-ladder phases, which might exist on top of superfluids and Mott insulators. Moreover, we demonstrate that quantum quenches of suitably chosen initial states can be used to probe the equilibrium properties in the transient dynamics. Concretely, we consider the instantaneous turning on of particle hopping along the rungs or legs in the synthetic flux-ladder model, with different initial particle distributions. We show that clear signatures of the biased-ladder phase and the Meissner phase can be observed in the transient dynamics. Second, we study the effect of finite temperatures in flux ladders. So far, most of the theoretical work on these systems has concentrated on zero-temperature phases while the finite-temperature regime remains largely unexplored. However, the question if and up to which temperature characteristic features of the ground-state phases persist is relevant in experimental realizations. In order to explore the finite-temperature regime, a matrix-product-state based purification approach for the simulation of strongly interacting bosons has been implemented. Our study is focused on chiral currents and momentum-distribution functions, which are key observables in ultracold quantum gases, and our main results concern the most prominent vortex liquid-to-Meissner crossover. We demonstrate that signatures of the vortex-liquid phase can still be detected at elevated temperatures from characteristic finite-momentum maxima in the momentum-distribution functions, while the vortex-liquid phase leaves weaker fingerprints in the chiral current. In order to determine the range of temperatures over which these signatures can be observed, we introduce a suitable measure for the contrast of these maxima. The results are condensed into a finite-temperature crossover diagram. Third, we investigate the Hall response in bosonic flux ladders. While flux ladders are the most simple lattice models giving rise to the Hall effect, the theoretical description of the many-body ground-state Hall response in these systems remains a tricky problem and an active line of research. In view of current quantum gas experiments, we discuss feasible schemes to extend measurements of the Hall polarization to a study of the Hall voltage, allowing for direct comparison with solid state systems. Most importantly, we report on characteristic zero crossings and a remarkable robustness of the Hall voltage with respect to interaction strengths, particle fillings, and ladder geometries, which is unobservable in the Hall polarization. Moreover, we investigate the site-resolved Hall response in spatially inhomogeneous quantum phases using a semiclassical approach. In conclusion, we present a brief summary of our work and touch on possible follow-up studies which are directly connected to the contents of this thesis.Flussleitermodelle beschreiben das komplexe Zusammenspiel von wechselwirkenden quantenmechanischen Teilchen, die sich unter dem Einfluss von effektiven Magnetfeldern in quasi-eindimensionalen Gittern bewegen. In den letzten Jahren konnten diese Modelle in optischen Gittern durch die Erzeugung von künstlichen Magnetfeldern für kalte Atome experimentell realisiert werden. Flussleitermodelle sind aufgrund ihrer formalen Einfachheit, ihrer reichhaltigen Phasendiagramme und gegenwärtiger Quantengasexperimente von großem Interesse. Die vorliegende Arbeit befasst sich mit der theoretischen Untersuchung von bosonischen Flussleitermodellen unter Verwendung numerischer Methoden, die auf Matrixproduktzuständen basieren. Wir erkunden Grundzustandsphasendiagramme mit dem Verfahren der Dichtematrix-Renormierungsgruppe. Darüber hinaus untersuchen wir thermische Zustände sowie dynamische Vielteilchenprobleme in Flussleitern mithilfe moderner Zeitentwicklungsmethoden. In einem einleitenden Teil dieser Arbeit wird das zentrale bosonische Flussleitermodell in den breiteren Forschungskontext eingeordnet. Wir diskutieren dessen wesentliche Eigenschaften und stellen die in dieser Arbeit verwendeten numerischen Methoden vor. Im Anschluss präsentieren wir die gewonnenen Forschungsergebnisse wie folgt. Zunächst liegt der Fokus auf Modellparametern, die durch ein angedachtes Experiment motiviert sind. In dem Experiment soll eine zweibeinige bosonische Flussleiter unter der Ausnutzung interner Spinzustände von kalten bosonischen Kaliumatomen realisiert werden. Wir zeigen, dass das zugehörige Grundzustandsphasendiagramm eine Mott-isolierende Meissner-Phase sowie superfluide und Mott-isolierende Biased-Ladder-Phasen aufweist. Mithilfe zeitabhängiger Simulationen demonstrieren wir, dass realistische Quantenquenchprotokolle es erlauben, Gleichgewichtseigenschaften der relevanten Grundzustandsphasen in der transienten Vielteilchendynamik zu beobachten und zu quantifizieren. Im Weiteren untersuchen wir die Quantenzustände von Flussleitern bei endlichen Temperaturen. Während die Nulltemperaturphasen von Flussleitermodellen im Zentrum zahlreicher theoretischer Arbeiten stehen, bleibt der Einfluss von Temperatureffekten auf die charakteristischen Grundzustandseigenschaften weitestgehend unerforscht. Dieser Einfluss spielt in Experimenten allerdings eine wichtige Rolle. Um die bei endlichen Temperaturen angenommenen Quantenzustände zu untersuchen bedienen wir uns einer Matrixproduktzustandsmethode, die im Rahmen dieser Arbeit implementiert wurde. Unsere Studie konzentriert sich auf chirale Randströme und charakteristische Quasiimpuls-Verteilungen, die in gegenwärtigen Quantengasexperimenten gemessen werden können. Für stark wechselwirkende Bosonen und ausgehend von dem Quantenphasenübergang von einer Vortex-Phase zu einer Meissner-Phase erarbeiten wir das zugehörige Crossoverdiagramm bei endlichen Temperaturen. Darüber hinaus untersuchen wir die Hall-Antwort bosonischer Flussleitermodelle. Flussleitern sind die minimalsten Gittermodelle, in denen sich ein Hall-Effekt untersuchen lässt. Dessen ungeachtet ist die Frage nach der Hall-Antwort in Quantenphasen, die auf Vielteilcheneffekten beruhen, theoretisch schwierig und Gegenstand aktueller Forschung. Vor dem Hintergrund gegenwärtiger Quantengasexperimente berichten wir über zeitabhängige Protokolle, mit denen sich Messungen der Hall-Polarisation auf Messungen der Hall-Spannung erweitern lassen. Durch umfangreiche numerische Simulationen zeigen wir, dass die Hall-Spannung in verschiedenen Quantenphasen eine große Robustheit im Hinblick auf die Wechselwirkungsstärke und die Teilchenfüllung aufweist. Diese Robustheit lässt sich in der Hall-Polarisation nicht beobachten. Wir untermauern unsere numerischen Ergebnisse mit semiklassischen Rechnungen und diskutieren die lokal aufgelöste Hall-Antwort in räumlich inhomogenen Vortexgitter-Phasen. Abschließend fassen wir die gewonnenen Ergebnisse kurz zusammen und erwähnen Folgestudien, die unmittelbar mit der vorliegenden Arbeit in Verbindung stehen

Probing the Hall Voltage in Synthetic Quantum Systems

In the context of experimental advances in the realization of artificial magnetic fields in quantum gases, we discuss feasible schemes to extend measurements of the Hall polarization to a study of the Hall voltage, allowing for direct comparison with solid state systems. Specifically, for the paradigmatic example of interacting flux ladders, we report on characteristic zero crossings and a remarkable robustness of the Hall voltage with respect to interaction strengths, particle fillings, and ladder geometries, which is unobservable in the Hall polarization. Moreover, we investigate the site-resolved Hall response in spatially inhomogeneous quantum phases.Comment: 6 pages, 5 figures + Supplemental Material (5 pages, 4 figures

Interacting bosonic flux ladders with a synthetic dimension: Ground-state phases and quantum quench dynamics

Flux ladders constitute the minimal setup enabling a systematic understanding of the rich physics of interacting particles subjected simultaneously to strong magnetic fields and a lattice potential. In this paper, the ground-state phase diagram of a flux-ladder model is mapped out using extensive density-matrix renormalization-group simulations. The emphasis is put on parameters which can be experimentally realized exploiting the internal states of potassium atoms as a synthetic dimension. The focus is on accessible observables such as the chiral current and the leg-population imbalance. Considering a particle filling of one boson per rung, we report the existence of a Mott-insulating Meissner phase as well as biased-ladder phases on top of superfluids and Mott insulators. Furthermore, we demonstrate that quantum quenches from suitably chosen initial states can be used to probe the equilibrium properties in the transient dynamics. Concretely, we consider the instantaneous turning on of hopping matrix elements along the rungs or legs in the synthetic flux-ladder model, with different initial particle distributions. We show that clear signatures of the biased-ladder phase can be observed in the transient dynamics. Moreover, the behavior of the chiral current in the transient dynamics is discussed. The results presented in this paper provide guidelines for future implementations of flux ladders in experimental setups exploiting a synthetic dimension.Comment: as published, with plotted data in json forma

Impact of the material and sintering protocol, layer thickness, and thermomechanical aging on the two-body wear and fracture load of 4Y-TZP crowns.

OBJECTIVES The aim of this study is to investigate the influence of the material and corresponding sintering protocol, layer thickness, and aging on the two-body wear (2BW) and fracture load (FL) of 4Y-TZP crowns. MATERIALS AND METHODS Multi-layer 4Y-TZP crowns in three thicknesses (0.5 mm/1.0 mm/1.5 mm) were sintered by high-speed (Zolid RS) or conventional (Zolid Gen-X) sintering. 2BW of ceramic and enamel antagonist after aging (1,200,000 mechanical-, 6000 thermal-cycles) was determined by 3D-scanning before and after aging and subsequent matching to determine volume and height loss (6 subgroups, n = 16/subgroup). FL was examined initially and after aging (12 subgroups, n = 16/subgroup). Fractographic analyses were performed using light-microscope imaging. Global univariate analysis of variance, one-way ANOVA, linear regression, Spearman's correlation, Kolgomorov-Smirnov, Mann-Whitney U, and t test were computed (alpha = 0.05). Weibull moduli were determined. Fracture types were analyzed using Ciba Geigy table. RESULTS Material/sintering protocol did not influence 2BW (crowns: p = 0.908, antagonists: p = 0.059). High-speed sintered Zolid RS presented similar (p = 0.325-0.633) or reduced (p < 0.001-0.047) FL as Zolid Gen-X. Both 4Y-TZPs showed an increased FL with an increasing thickness (0.5(797.3-1429 N) < 1.0(2087-2634 N) < 1.5(2683-3715 N)mm; p < 0.001). For most groups, aging negatively impacted FL (p < 0.001-0.002). Five 0.5 mm specimens fractured, four showed cracks during and after aging. CONCLUSIONS High-speed sintered crowns with a minimum thickness of 1.0 mm showed sufficient mechanical properties to withstand masticatory forces, even after a simulated aging period of 5 years. CLINICAL RELEVANCE Despite the manufacturer indicating a thickness of 0.5 mm to be suitable for single crowns, a minimum thickness of 1.0 mm should be used to ensure long-term satisfactory results

Finite-temperature properties of interacting bosons on a two-leg flux ladder

Quasi-one-dimensional lattice systems such as flux ladders with artificial gauge fields host rich quantum-phase diagrams that have attracted great interest. However, so far, most of the work on these systems has concentrated on zero-temperature phases while the corresponding finite-temperature regime remains largely unexplored. The question if and up to which temperature characteristic features of the zero-temperature phases persist is relevant in experimental realizations. We investigate a two-leg ladder lattice in a uniform magnetic field and concentrate our study on chiral edge currents and momentum-distribution functions, which are key observables in ultracold quantum-gas experiments. These quantities are computed for hard-core bosons as well as noninteracting bosons and spinless fermions at zero and finite temperatures. We employ a matrix-product-state based purification approach for the simulation of strongly interacting bosons at finite temperatures and analyze finite-size effects. Our main results concern the vortex-fluid-to-Meissner crossover of strongly interacting bosons. We demonstrate that signatures of the vortex-fluid phase can still be detected at elevated temperatures from characteristic finite-momentum maxima in the momentum-distribution functions, while the vortex-fluid phase leaves weaker fingerprints in the local rung currents and the chiral edge current. In order to determine the range of temperatures over which these signatures can be observed, we introduce a suitable measure for the contrast of these maxima. The results are condensed into a finite-temperature crossover diagram for hard-core bosons