We propose a highly scalable method to compute the statistics of charge transfer in driven conductors. The framework can be applied in situations of nonzero temperature, strong coupling to terminals, and in the presence of nonperiodic light-matter interactions, away from equilibrium. The approach combines the so-called mesoscopic leads formalism with full counting statistics. It results in a generalized quantum master equation that dictates the dynamics of current fluctuations and higher order moments of the probability distribution function of charge exchange. For generic time-dependent quadratic Hamiltonians, we provide closed-form expressions for computing noise in the nonperturbative regime of the parameters of the system, reservoir, or system-reservoir interactions. Having access to the full dynamics of the current and its noise, the method allows us to compute the variance of charge transfer over time in nonequilibrium configurations. The dynamics reveal that in driven systems, the average noise should be defined operationally with care over which period of time is covered.
Weniger anzeigenMany-body localization is believed to be generically unstable in quantum systems with continuous non-Abelian symmetries, even in the presence of strong disorder. Breaking these symmetries can stabilize the localized phase, leading to the emergence of an extensive number of quasilocally conserved quantities known as local integrals of motion, or l bits. Using a sophisticated nonperturbative technique based on continuous unitary transforms, we investigate the one-dimensional Hubbard model subject to both spin and charge disorder, compute the associated l bits and demonstrate that the disorder gives rise to a novel form of spin-charge separation. We examine the role of symmetries in delocalizing the spin and charge degrees of freedom, and show that while symmetries generally lead to delocalization through multiparticle resonant processes, certain subsets of states appear stable.
Weniger anzeigenDuring the Grand Finale orbits, Cassini’s Cosmic Dust Analyzer (CDA) recorded in situ mass spectra of ice and mineral nanodust grains ejected from Saturn’s main rings falling into the planet’s atmosphere. We present a compositional analysis of the mineral dust fraction employing a spectral deconvolution method to determine the elemental composition of these grains. The results indicate a relatively homogenous composition of exclusively Mg-rich silicates, with Mg, Si, and Ca close to CI chondritic abundances but a significant depletion in Fe and only traces of organic material at best. The Fe depletion becomes even more pronounced when compared to Fe-rich interplanetary dust particles encountered by CDA in the Saturnian system, which are assumed to contaminate and darken the main rings over time. We discuss potential explanations for the depletion, from which we favour compositional alteration of the infalling dust grains by impact-triggered chemistry in combination with dynamical selection effects and instrumental bias as the most plausible ones. This might cause an accumulation of Fe in the main rings over time, most likely in the form of oxides.
Weniger anzeigenWalker-Wang models are fixed-point models of topological order in 3+1 dimensions constructed from a braided fusion category. For a modular input category M, the model itself is invertible and is believed to be in a trivial topological phase, whereas its standard boundary is supposed to represent a (2+1)-dimensional chiral phase. In this work we explicitly show triviality of the model by constructing an invertible domain wall to vacuum as well as a disentangling generalized local unitary circuit in the case where M is a Drinfeld center. Moreover, we show that if we allow for fermionic (auxiliary) degrees of freedom inside the disentangling domain wall or circuit, the model becomes trivial for a larger class of modular fusion categories, namely, those in the Witt classes generated by the Ising unitary modular tensor category. We also discuss general (noninvertible) boundaries of general Walker-Wang models and describe a simple axiomatization of extended topological quantum field theory in terms of tensors.
Weniger anzeigenIt is widely believed that many-body localization in one dimension is fragile and can be easily destroyed by thermal inclusions; however, there are still many open questions regarding the stability of the localized phase and under what conditions it breaks down. Here I construct models with dilute disorder, which interpolate between translationally invariant and fully random models, in order to study the breakdown of localization. This opens up the possibility to controllably increase the density of thermal regions and examine the breakdown of localization as this density is increased. At strong disorder, the numerical results are consistent with commonly used diagnostics for localization even when the concentration of thermalizing regions is high. At moderate disorder, I present evidence for slow dynamics and subdiffusive transport across a large region of the phase diagram, suggestive of a “bad metal” phase. This suggests that dilute disorder may be a useful effective model for studying Griffiths effects in many-body localization, and perhaps also in a wider class of disordered systems.
Weniger anzeigenPhase spaces as given by the Wigner distribution function provide a natural description of infinite-dimensional quantum systems. They are an important tool in quantum optics and have been widely applied in the context of time–frequency analysis and pseudo-differential operators. Phase-space distribution functions are usually specified via integral transformations or convolutions which can be averted and subsumed by (displaced) parity operators proposed in this work. Building on earlier work for Wigner distribution functions (Grossmann in Commun Math Phys 48(3):191–194, 1976. https://doi.org/10.1007/BF01617867), parity operators give rise to a general class of distribution functions in the form of quantum-mechanical expectation values. This enables us to precisely characterize the mathematical existence of general phase-space distribution functions. We then relate these distribution functions to the so-called Cohen class (Cohen in J Math Phys 7(5):781–786, 1966. https://doi.org/10.1063/1.1931206) and recover various quantization schemes and distribution functions from the literature. The parity operator approach is also applied to the Born–Jordan distribution which originates from the Born–Jordan quantization (Born and Jordan in Z Phys 34(1):858–888, 1925. https://doi.org/10.1007/BF01328531). The corresponding parity operator is written as a weighted average of both displacements and squeezing operators, and we determine its generalized spectral decomposition. This leads to an efficient computation of the Born–Jordan parity operator in the number-state basis, and example quantum states reveal unique features of the Born–Jordan distribution.
Weniger anzeigenIcy moons like Enceladus, and perhaps Europa, emit material sourced from their subsurface oceans into space via plumes of ice grains and gas. Both moons are prime targets for astrobiology investigations. Cassini measurements revealed a large compositional diversity of emitted ice grains with only 1 to 4% of Enceladus’s plume ice grains containing organic material in high concentrations. Here, we report experiments simulating mass spectra of ice grains containing one bacterial cell, or fractions thereof, as encountered by advanced instruments on board future space missions to Enceladus or Europa, such as the SUrface Dust Analyzer onboard NASA’s upcoming Europa Clipper mission at flyby speeds of 4 to 6 kilometers per second. Mass spectral signals characteristic of the bacteria are shown to be clearly identifiable by future missions, even if an ice grain contains much less than one cell. Our results demonstrate the advantage of analyses of individual ice grains compared to a diluted bulk sample in a heterogeneous plume.
Weniger anzeigenSharing multi-partite quantum entanglement between parties allows for diverse secure communication tasks to be performed. Among them, conference key agreement (CKA) - an extension of key distribution to multiple parties - has received much attention recently. Interestingly, CKA can also be performed in a way that protects the identities of the participating parties, therefore providing anonymity. In this work, we propose an anonymous CKA protocol for three parties that is implemented in a highly practical network setting. Specifically, a line of quantum repeater nodes is used to build a linear cluster state among all nodes, which is then used to anonymously establish a secret key between any three of them. The nodes need only share maximally entangled pairs with their neighbours, therefore avoiding the necessity of a central server sharing entangled states. This linear chain setup makes our protocol an excellent candidate for implementation in future quantum networks. We explicitly prove that our protocol protects the identities of the participants from one another and perform an analysis of the key rate in the finite regime, contributing to the quest of identifying feasible quantum communication tasks for network architectures beyond point-to-point.
Weniger anzeigenThe problem of characterizing GKLS-generators and CP-maps with an invariant von Neumann algebra A appeared in different guises in the literature. We prove two unifying results, which hold even for weakly closed *-algebras: first, we show how to construct a normal form for A-invariant GKLS-generators, if a normal form for A-invariant CP-maps is known — rendering the two problems essentially equivalent. Second, we provide a normal form for A-invariant CP-maps if A is atomic (which includes the finite-dimensional case). As an application we reproduce several results from the literature as direct consequences of our characterizations and thereby point out connections between different fields.
Weniger anzeigenWe examine the effectiveness and resilience of achieving quantum gates employing three approaches stemming from quantum control methods: counterdiabatic driving, Floquet engineering, and inverse engineering. We critically analyze their performance in terms of the gate infidelity, the associated resource overhead based on energetic cost, the susceptibility to timekeeping errors, and the degradation under environmental noise. Despite significant differences in the dynamical path taken, we find a broadly consistent behavior across the three approaches in terms of the efficacy of implementing the target gate and the resource overhead. Furthermore, we establish that the functional form of the control fields plays a crucial role in determining how faithfully a gate operation is achieved. Our results are demonstrated for single-qubit gates, with particular focus on the Hadamard gate, and we discuss the extension to N-qubit operations.
Weniger anzeigenAlternative Wege in den Lehrer*innenberuf wurden in den vergangenen Jahren für unterschiedliche Fächer und Schulformen in nahezu allen Bundesländern geschaffen. Um auch die Qualität alternativer Wege in den Lehrer*innenberuf gewährleisten zu können, bedarf es sowohl der Einführung von (Mindest-)Standards als auch empirischer Forschung zu den professionellen Handlungskompetenzen der über alternative Wege qualifizierten Lehrer*innen. Der alternative Weg des Quereinstiegs während des Studiums wird an der Freien Universität Berlin seit 2016 in Form das Modellstudiengangs ‚Q-Master‘ erprobt und durch evaluative Forschung begleitet: Im Studienfach Physik wird exemplarisch die Ausprägung und Entwicklung fachlicher Aspekte professioneller Handlungskompetenz mittels Tests und Fragebögen längsschnittlich erfasst und mit Studierenden des regulären Lehramtsmasters an der FU Berlin verglichen. Ergänzt wird dieses Vorgehen durch leitfadengestützte Interviews zu zwei Befragungszeitpunkten.
Die Ergebnisse der quantitativen Begleitforschung an der FU Berlin deuten auf eine Ausprägung und Entwicklung professioneller Kompetenzen der Q-Masterstudierenden hin, welche mit der von Studierenden des regulären Lehramtsmasters vergleichbar ist. Die Auswertung der Interviewdaten deutet bislang darauf hin, dass weniger geradlinige Berufsbiografien nicht nur bei Q-Masterstudierende vorkommen. Als wertvoll für die Professionalisierung schätzen die Studierenden das Praxissemester sowie fachdidaktische und bildungswissenschaftliche Lehrveranstaltungen ein, während die Nützlichkeit umfänglicher fachwissenschaftlichen Lehrinhalte für die spätere Berufspraxis infrage gestellt wird.
Der Beitrag stellt Ergebnisse der Begleitforschung zum Q-Master an der FU Berlin vor und diskutiert diese hinsichtlich der Implikationen für die Lehrer*innenbildung.
Weniger anzeigenEine reflexive Haltung gegenüber der eigenen Lehrtätigkeit gilt als Schlüsselqualifikation in Bezug auf die Professionalisierung von Lehrer:innen in allen Didaktiken (GFD, 2004, S. 4). Das universitäre Seminarformat Lehr-Lern-Labor (LLLS) kann diese Haltung fördern (Rehfeldt et al., 2018). Das Lehrformat eignet sich außerdem zur Steigerung des Professionswissens und der unterrichtlichen Handlungsfähigkeit angehender Lehrer:innen (Rehfeldt et al., 2020; Brämer & Köster, 2021). Dieser Beitrag stellt, neben der grundsätzlichen Konzeption des Seminarformats, dessen Implementierung in vier verschiedenen Fachdidaktiken (Didaktiken des Englischen, der Geschichte, der Physik und Sachunterricht und seine Didaktik) vor. Ein Fokus liegt dabei auf der unterschiedlichen Umsetzung der Reflexionsphasen.
Weniger anzeigenBackground: Over 80% of the morbidity and mortality related to non-communicable diseases (NCDs) occurs in low-income and middle-income countries (LMICs). Community health workers (CHWs) may improve disease control and medication adherence among patients with NCDs in LMICs, particularly in sub-Saharan African settings. In Uganda, and the majority of LMICs, management of uncontrolled hypertension remains limited in constrained health systems. Intervening at the primary care level, using CHWs to improve medical treatment outcomes has not been well studied. We aim to determine the effectiveness of a CHW-led intervention in blood pressure control among confirmed hypertensive patients and patient-related factors associated with uncontrolled hypertension.
Methods: We will conduct a stepped-wedge cluster randomized controlled trial study of 869 adult patients with hypertension attending two NCD clinics to test the effectiveness, acceptability, and fidelity of a CHW-led intervention. The multi-component intervention will be centered on monthly household visits by trained CHWs for a period of 1 year, consisting of the following: (1) blood pressure and sugar monitoring, (2) BMI monitoring, (3) cardiovascular disease risk assessment, (4) using checklists to guide monitoring and referral to clinics, and (5) healthy lifestyle counseling and education. During home visits, CHWs will remind patients of follow-up visits. We will measure blood pressure at baseline and 3-monthly for the entire cohort. We will conduct individual-level mixed effects analyses of study data, adjusting for time and clustering by patient and community.
Conclusion: The results of this study will inform community delivered HTN management across a range of LMIC settings.
Weniger anzeigenBackground: Frailty is expressed by a reduction in physical capacity, mobility, muscle strength, and endurance. (Pre-) frailty is present in up to 42% of the older surgical population, with an increased risk for peri- and postoperative complications. Consequently, these patients often suffer from a delayed or limited recovery, loss of autonomy and quality of life, and a decrease in functional and cognitive capacities. Since frailty is modifiable, prehabilitation may improve the physiological reserves of patients and reduce the care dependency 12 months after surgery.
Methods: Patients >= 70 years old scheduled for elective surgery or intervention will be recruited in this multicenter, randomized controlled study, with a target of 1400 participants with an allocation ratio of 1:1. The intervention consists of (1) a shared decision-making process with the patient, relatives, and an interdisciplinary and interprofessional team and (2) a 3-week multimodal, individualized prehabilitation program including exercise therapy, nutritional intervention, mobility or balance training, and psychosocial interventions and medical assessment. The frequency of the supervised prehabilitation is 5 times/week for 3 weeks. The primary endpoint is defined as the level of care dependency 12 months after surgery or intervention.
Discussion: Prehabilitation has been proven to be effective for different populations, including colorectal, transplant, and cardiac surgery patients. In contrast, evidence for prehabilitation in older, frail patients has not been clearly established. To the best of our knowledge, this is currently the largest prehabilitation study on older people with frailty undergoing general elective surgery.
Weniger anzeigenBackground: Peanuts (PN) and tree nuts (TN) are among the most frequent elicitors of food allergy and can lead to life-threatening reactions. The current advice for allergic patients is to strictly avoid the offending food independently of their individual threshold level, whereas sensitized patients without allergic symptoms should frequently consume the food to avoid (re-)development of food allergy. The aim of this trial is to investigate (I) whether the consumption of low allergen amounts below the individual threshold may support natural tolerance development and (II) to what extent regular allergen consumption in sensitized but tolerant subjects prevents the (re-)development of PN or TN allergy.
Methods: The TINA trial consisting of (part I) a randomized, controlled, open, parallel group, single-center, superiority trial (RCT), and (part II) a prospective observational exploratory cohort study. Children and adults (age 1-67 years) with suspected or known primary PN and/or TN allergy will undergo an oral food challenge (OFC) to determine their clinical reactivity and individual threshold. In the RCT, 120 PN or TN allergic patients who tolerate >= 100 mg of food protein will be randomized (1:1 ratio) to consumption of products with low amounts of PN or TN on a regular basis or strict avoidance for 1 year. The consumption group will start with 1/100 of their individual threshold, increasing the protein amount to 1/50 and 1/10 after 4 and 8 months, respectively. The primary endpoint is the clinical tolerance to PN or TN after 1 year assessed by OFC. In the cohort study, 120 subjects sensitized to PN and/or TN but tolerant are advised to regularly consume the food and observed for 1 year. The primary endpoint is the maintenance of clinical tolerance to PN and/or TN after 1 year assessed by challenging with the former tolerated cumulative dose.
Discussion: This clinical trial will help to determine the impact of allergen consumption versus avoidance on natural tolerance development and whether the current dietary advice for PN or TN allergic patients with higher threshold levels is still valid.
Weniger anzeigenAim
Squamate fitness is affected by body temperature, which in turn is influenced by environmental temperatures and, in many species, by exposure to solar radiation. The biophysical drivers of body temperature have been widely studied, but we lack an integrative synthesis of actual body temperatures experienced in the field, and their relationships to environmental temperatures, across phylogeny, behaviour and climate.
Location
Global (25 countries on six continents).
Taxa
Squamates (210 species, representing 25 families).
Methods
We measured the body temperatures of 20,231 individuals of squamates in the field while they were active. We examined how body temperatures vary with substrate and air temperatures across taxa, climates and behaviours (basking and diel activity).
Results
Heliothermic lizards had the highest body temperatures. Their body temperatures were the most weakly correlated with substrate and air temperatures. Body temperatures of non-heliothermic diurnal lizards were similar to heliotherms in relation to air temperature, but similar to nocturnal species in relation to substrate temperatures. The correlation of body temperature with air and substrate temperatures was stronger in diurnal snakes and non-heliothermic lizards than in heliotherms. Body-substrate and body-air temperature correlations varied with mean annual temperatures in all diurnal squamates, especially in heliotherms. Thermal relations vary with behaviour (heliothermy, nocturnality) in cold climates but converge towards the same relation in warm climates. Non-heliotherms and nocturnal species body temperatures are better explained by substrate temperature than by air temperature. Body temperature distributions become left-skewed in warmer-bodied species, especially in colder climates.
Main Conclusions
Squamate body temperatures, their frequency distributions and their relation to environmental temperature, are globally influenced by behavioural and climatic factors. For all temperatures and climates, heliothermic species' body temperatures are consistently higher and more stable than in other species, but in regions with warmer climate these differences become less pronounced. A comparable variation was found in non-heliotherms, but in not nocturnal species whose body temperatures were similar to air and substrate irrespective of the macroclimatic context.
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