Austrian Academy of Sciences (OeAW)
Recent publications
A simple argument is presented that explicitly shows how to construct an arbitrary quantum gate acting on orbital angular momentum (OAM) of single photons. The scheme can be applied to implement subspace multiplexing, where a single high-dimensional OAM qudit represents effectively a stack of multiple independent lower-dimensional qudits. A special subclass of unitaries composed of single-photon controlled gates is studied in detail and notable examples of the general approach are discussed. The generalization of the simple argument leads to the parallelization scheme, which results in the savings of resources. The presented schemes utilize only conventional optical elements and apply not only to single photons but also to classical light.
We present an approximately C1-smooth multi-patch spline construction which can be used in isogeometric analysis (IGA). The construction extends the one presented in [1] for two-patch domains. A key property of IGA is that it is simple to achieve high order smoothness within a single patch. However, to represent more complex geometries one often uses a multi-patch construction. In this case, the global continuity for the basis functions is in general only C0. Therefore, to obtain C1-smooth isogeometric functions, a special construction for the basis is needed. Such spaces are of interest when solving numerically fourth-order problems, such as the biharmonic equation or Kirchhoff–Love plate/shell formulations, using an isogeometric Galerkin method. Isogeometric spaces that are globally C1 over multi-patch domains can be constructed as in [2], [3], [4], [5], [6]. The constructions require geometry parametrizations that satisfy certain constraints along the interfaces, so-called analysis-suitable G1 parametrizations. To allow C1 spaces over more general multi-patch parametrizations, one needs to increase the polynomial degree and/or to relax the C1 conditions. Thus, we define function spaces that are not exactly C1 but only approximately. We adopt the construction for two-patch domains, as developed in [1], and extend it to more general multi-patch domains. We employ the construction for a biharmonic model problem and compare the results with Nitsche’s method. We compare both methods over complex multi-patch domains with non-trivial interfaces. The numerical tests indicate that the proposed construction converges optimally under h-refinement, comparable to the solution using Nitsche’s method. In contrast to weakly imposing coupling conditions, the approximate C1 construction is explicit and no additional terms need to be introduced to stabilize the method/penalize the jump of the derivative at the interface. Thus, the new proposed method can be used more easily as no parameters need to be estimated.
High-pressure-torsion (HPT) processing introduces a large density of dislocations that form sub-grain boundaries within the refined nano-scale structure, leading to changes in precipitate morphology compared to hot-rolled maraging steels. The impact of such nanostructuring on the deformation and fracture micro-mechanisms is being reported for the first time using in-situ characterization techniques along with transmission electron microscopy and atom probe tomography analysis, in this study. Digital image correlation has been used to quantify the full field strain maps in regions of severe strain localization as well as to determine the fracture toughness through critical crack tip opening displacements. It is seen that the phenomenon of planar slip leads to strain softening under uniaxial deformation and to crack branching under a triaxial stress state in hot rolled maraging steels. On the other hand, nano-structuring after HPT processing creates a large number of high angle grain boundaries as dislocation barriers, leading to strain hardening under uniaxial tension and nearly straight crack path with catastrophic fracture under triaxial stress state. Upon overaging, the hot-rolled sample shows signature of transformation induced plasticity under uniaxial tension, which is absent in the HPT processed overaged samples, owing to the finer reverted austenite grains containing higher Ni concentration in the latter. In the overaged fracture test samples of both the hot-rolled and HPT conditions, crack tips show a signature of strain induced transformation of the reverted austenite to martensite, due to the accompanying severe strain gradients. This leads to a higher fracture toughness even while achieving high strengths in the overaged conditions of the nanocrystalline HPT overaged samples. The results presented here will aid in design of suitable heat treatment or microstructure engineering of interface dominated nano-scale maraging steels with improved damage tolerance.
We study the computation of the zero set of the Bargmann transform of a signal contaminated with complex white noise, or, equivalently, the computation of the zeros of its short-time Fourier transform with Gaussian window. We introduce the adaptive minimal grid neighbors algorithm (AMN), a variant of a method that has recently appeared in the signal processing literature, and prove that with high probability it computes the desired zero set. More precisely, given samples of the Bargmann transform of a signal on a finite grid with spacing $$\delta $$ δ , AMN is shown to compute the desired zero set up to a factor of $$\delta $$ δ in the Wasserstein error metric, with failure probability $$O(\delta ^4 \log ^2(1/\delta ))$$ O ( δ 4 log 2 ( 1 / δ ) ) . We also provide numerical tests and comparison with other algorithms.
We report on the nonlinear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO, observed through high harmonic generation. While the linear optical response of the material is largely unchanged when cooling across the phase transitions, the nonlinear optical response sensitively imprints two critical points, one at the critical temperature of the cuprate with the exponential growth of the surface harmonic yield in the superconducting phase and another critical point, which marks the transition from strange metal to pseudogap phase. To reveal the underlying microscopic quantum dynamics, a strong-field quasi-Hubbard model was developed, which describes the measured optical response dependent on the formation of Cooper pairs. Further, the theory provides insight into the carrier scattering dynamics and allows us to differentiate between the superconducting, pseudogap, and strange metal phases. The direct connection between nonlinear optical response and microscopic dynamics provides a powerful methodology to study quantum phase transitions in correlated materials. Further implications are light wave control over intricate quantum phases, light–matter hybrids, and application for optical quantum computing.
Investigations of possible violations of the Pauli exclusion principle represent critical tests of the microscopic space-time structure and properties. Space-time noncommutativity provides a class of universality for several quantum gravity models. In this context the VIP-2 lead experiment sets the strongest bounds, searching for the Pauli exclusion principle violating atomic transitions in lead, excluding the θ-Poincaré noncommutative quantum gravity models far above the Planck scale for nonvanishing θμν electriclike components, and up to 6.9×10−2 Planck scales if θ0i=0.
Zusammenfassung Für die erfolgreiche Umsetzung von partizipativen und co-kreativen Stadtentwicklungsprozessen stellt die Ansprache und die Beteiligung von betroffenen Akteur*innen, insbesondere der Eigentümer*innen, eine zentrale Voraussetzung dar. Umgekehrt ist das Wissen darüber, wem die Stadt eigentlich gehört, häufig nur sehr eingeschränkt in adäquater Form zugänglich. Dieser Beitrag diskutiert anhand der gründerzeitlichen Bestandsstadt in Wien, die durch eine zunehmende Zersplitterung der Eigentumsstrukturen gekennzeichnet ist, die Potenziale, die sich aus einer liegenschaftsgenauen Eigentumsanalyse ergeben. Grundlage bildet eine Datenbank, bei der auf Grundlage der Katastralmappe unterschiedliche Registerdaten, insbesondere das Grundbuch, mit Open-Source-Datenbeständen verschnitten worden sind. Anhand dreier konkreter Anwendungsbeispiele zeigt der Beitrag das große Potenzial dieser auf Individualdaten basierender Stadtraumanalysen für die Planungspraxis. Auf Ebene der Baublöcke erfolgt eine Analyse der Eigentümer*innen-Strukturen und deren Zersplitterung für den gesamten Stadtraum. Auf Liegenschafts- und Gebäudeebene werden in einem ausgewählten gründerzeitlichen Grätzel die Potenziale für Klimaschutz- bzw. Anpassungsstrategien bewertet: einerseits für die Errichtung von Solaranlagen auf Dachflächen sowie andererseits für Fassadenbegrünungen.
We investigate the Hilbert complex of elasticity involving spaces of symmetric tensor fields. For the involved tensor fields and operators we show closed ranges, Friedrichs/Poincaré type estimates, Helmholtz-type decompositions, regular decompositions, regular potentials, finite cohomology groups, and, most importantly, new compact embedding results. Our results hold for general bounded strong Lipschitz domains of arbitrary topology and rely on a general functional analysis framework (FA-ToolBox). Moreover, we present a simple technique to prove the compact embeddings based on regular decompositions/potentials and Rellich's selection theorem, which can be easily adapted to any Hilbert complex.
Three-dimensional quantum gases of strongly dipolar atoms can undergo a crossover from a dilute gas to a dense macrodroplet, stabilized by quantum fluctuations. Adding a one-dimensional optical lattice creates a platform where quantum fluctuations are still unexplored, and a rich variety of phases may be observable. We employ Bloch oscillations as an interferometric tool to assess the role quantum fluctuations play in an array of quasi-two-dimensional Bose-Einstein condensates. Long-lived oscillations are observed when the chemical potential is balanced between sites, in a region where a macrodroplet is extended over several lattice sites. Further, we observe a transition to a state that is localized to a single lattice plane–driven purely by interactions–marked by the disappearance of the interference pattern in the momentum distribution. To describe our observations, we develop a discrete one-dimensional extended Gross-Pitaevskii theory, including quantum fluctuations and a variational approach for the on-site wavefunction. This model is in quantitative agreement with the experiment, revealing the existence of single and multisite macrodroplets, and signatures of a two-dimensional bright soliton.
Utilizing four-point joint observations by Magnetospheric Multiscale Spacecraft (MMS), we investigate the main features of the current sheet frozen in (CSFI) the bursty bulk flow. Typical event on the steady long-lasting BBF on July 23, 2017 shows the enhanced dawn-dusk current (Jy0) in the CSFI (β ~ 10). The magnitude of the Jy0 in the CSFI is about 5.5 nA/m². The CSFI is highly turbulent, with the ratio of ∆J/J0 of ~ 2 (where ∆J is perturbed J). The turbulent CSFI is characterized by intermittent current coherent structures. The magnitude of the spiky-J at coherent structures is typically above 30 nA/m². Spectrum analysis exhibits that BBF turbulence follows distinct dissipation laws inside and outside the CSFI. Based on MMS observations, we propose a new model of the BBF in the framework of magnetohydrodynamics. In this model, the BBF is depicted as a closed plasma system with the localized current sheet frozen at the center of the flow (Taylor’s hypothesis). In the light of principle of Helmholtz-decomposition, the BBF motion in the tail plasma sheet is explained. The model also predicts the thermal expansion of the BBF after leaving the reconnection source region.
High-dimensional entanglement is significant for the fundamental studies of quantum physics and offers unique advantages in various quantum information processing (QIP) tasks. Integrated quantum devices have recently emerged as a promising platform for creating, processing, and detecting complex high-dimensional entangled states. A crucial step towards practical quantum technologies is to verify that these devices work reliably with an optimal strategy. In this work, we experimentally implement an optimal quantum verification strategy on a three-dimensional maximally entangled state using local projective measurements on a silicon photonic chip. A 95% confidence is achieved from 1190 copies to verify the target quantum state. The obtained scaling of infidelity as a function of the number of copies is -0.5497±0.0002, exceeding the standard quantum limit of -0.5 with 248 standard deviations. Our results indicate that quantum state verification could serve as an efficient tool for complex quantum measurement tasks.
In 1999, four editorials in the journal Biological Chemistry commemorate how, since the 1980s, Vienna has transformed from a "[peripheral] outpost near the Iron Curtain" to a "central hub" for life science research. A closer look at these texts reveals the explicit and implicit role of drawing maps for and within science, depicting centers, peripheries and-in this case-geopolitically real and allegorical "iron curtains". Based on this observation and the issues it raises, I reexamine the pertinent empirical material covering relevant times, places, (sub-) disciplines and institutions, as well as the period after 2000. I deal with "molecularization" in biology, (sub)disciplinary differentiation, internationalization, as well as changes in public-private relations and a pair of complementary concepts of innovation and tradition. Thus, I retrace the establishment of a techno-epistemic culture in a local, disciplinary context.
Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called “metallicity”)1-3, and thus formation processes of the primary atmospheres of hot gas giants4-6. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets7-9. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections due to the lack of unambiguous spectroscopic identification10-12. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science Program (ERS)13,14. The data used in this study span 3.0 - 5.5 µm in wavelength and show a prominent CO2 absorption feature at 4.3 µm (26σ significance). The overall spectrum is well matched by one-dimensional, 10x solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide, and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 µm that is not reproduced by these models.
Ceramic assemblages from the Bukhara Oasis show an interesting mix of vessel forms and decorative styles, specifically in pre-Islamic times. Some elements of the tableware bear resemblance to material from adjacent regions in the south-west and south-east, including Margiana and Bactria, while others, specifically the storage vessels, appear to be inspired by the north-west or eastern areas, such as Khoresm and Chach. Surface coatings and slip paint proved to be highly significant in identifying these distinct cultural links. Drawing upon samples from the recent excavations by the MAFOUB project, this paper will trace the various cultural strains through analyzing the use of slip and slip-paint as an exemplary feature in the ceramic assemblages of the Bukhara Oasis from antiquity to the early Islamic period. Individual decorative patterns appear to be restricted to certain parts of the vessel repertoire. While coated vessels firmly belong to the tableware inventory, cursory applied slip paint with drizzling effects is mostly observed on containers and storage jars. Some slip painted decorations illustrate the considerable variation this technique enjoyed within the Bukhara Oasis. Our diachronic study highlights these diversities and follows the implied cultural alliances to shed light on Bukhara's position and role within the Central Asian neighborhood.
We establish novel uniqueness results for the Gabor phase retrieval problem: if G:L2(R)→L2(R2) denotes the Gabor transform then every f∈L4[−c2,c2] is determined up to a global phase by the values |Gf(x,ω)| where (x,ω) are points on the lattice b−1Z×(2c)−1Z and b>0 is an arbitrary positive constant. This for the first time shows that compactly supported, complex-valued functions can be uniquely reconstructed from lattice samples of their spectrogram. Moreover, by making use of recent developments related to sampling in shift-invariant spaces by Gröchenig, Romero and Stöckler, we prove analogous uniqueness results for functions in shift-invariant spaces with Gaussian generator. Generalizations to nonuniform sampling are also presented. Finally, we compare our results to the situation where the considered signals are assumed to be real-valued.
The gendered memorializing of the War of Resistance against Japan (1931–45) has been an important part of China’s war memory politics in all of the different phases it has undergone since 1945. In the Mao era, the iconography of the ‘Anti-Japanese female revolutionary martyrdoms’ rose to prominence, while the following reformation period consolidated a she-victim/he-hero dichotomy most forcefully characterized by the visualization of the Nanjing Massacre through violated female bodies symbolizing the nation’s victimhood. This article argues that in the Xi Jinping era, women’s roles in museums have begun to transform again. Coming from the viewpoint of a feminist critique, it approaches five prominent war museums in mainland China with gender as its main analytical category, studying women’s representations in the memorial spaces and exhibitions. It suggests that the current trends introduced the role of survivor of sexual violence and female soldier into the museal landscape, slightly complicating the previous gendered repertoires in the war’s musealization. By exploring the Chinese sociocultural themes of ‘chastity martyrdom’ and ‘female warriors’ and the multi-layered politics of the so-called ‘comfort women’ it discusses the extent to which the strategies used to portray women serve patriarchal nationalism rather than women’s interests.
The Gleisdorf Formation (Fm.) deposits in the clay pit at Gratkorn, Styria, Austria, are dated to 12.2–12 Ma, and are of late middle Miocene age (late Serravallian or Sarmatian). To reconstruct the paleovegetation and estimate the paleoclimate at this important vertebrate site, the palynoflora close to the boundary between the vertebrate-bearing layers of the Gratkorn Fm. and the overlying limnic clay deposits of the Gleisdorf Fm. was investigated. Using the single-grain method, 140 palynomorphs were identified. The palynoflora suggests that the paleovegetation was characterised by well-drained lowland and upland forests, riparian forest, and swamp forests. Depending on the dominating tree species, lowland and upland forests might have had closed or more open canopies. Open habitats included wet meadows and shrublands. In addition, conifers were present in the swampy lowlands and the forested uplands. The most prominent paleoclimatic signatures of the palynoflora indicate a fully humid warm temperate climate, with hot to warm summers and cool winters (Cfa-, Cfb-climate), and a seasonal climate with cool and drier winters and hot to warm and wetter summers (Cwa-, Cwb-climate). Our results align with existing studies bordering the Styrian Basin and support the presence of subtropical to warm-temperate vegetation around Gratkorn during the Sarmatian.
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703 members
Viktor Johannes Bruckman
  • Commission for Interdisciplinary Ecological Studies
Michael Nentwich
  • Institute of Technology Assessment
René Fries
  • Institute of Technology Assessment
Helge Torgersen
  • Institute of Technology Assessment
Michael Ornetzeder
  • Institute of Technology Assessment
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