In 1998, one of the fundamental assumptions in quantum mechanics, that the Hamiltonian describing a quantum system has to be Hermitian, was overturned. The existence of an entire class of Hamiltonians that are non-Hermitian yet still possess real eigenvalues was discovered. These non-Hermitian Hamiltonians describe PT-symmetric systems, which are systems that are invariant under the combined operations of parity-inversion and time-reversal. Currently, it is still under debate what implications PT-symmetry has for quantum physics. Yet in photonics, PT-symmetry can be readily realized by a proper distribution of gain and loss in the system, making photonics the ideal platform for studying the physics of PT-symmetric systems. Indeed, various effects of PT-symmetry such as non-orthogonal eigenmodes, non-reciprocal evolution of light, and diffusive coherent transport have been demonstrated on a photonic platform, and inspired applications in lasers and optical diodes. So far, these photonic experiments have been purely classical and the full impact of PT-symmetry on the evolution of light is still unclear. Quantum evolution of light in PT-symmetric systems is completely unexplored territory with lots of new physics to be unravelled. Therefore, the objective of this proposal is to for the first time experimentally investigate the evolution of quantum states in non-Hermitian systems. In particular, the project will study the quantum evolution of multiple correlated photons injected in PT-symmetric integrated photonic structures fabricated using direct laser-writing technology. The aim is to investigate how modifying the non-Hermitian Hamiltonian of the system influences photon correlations, expecting to demonstrate novel behaviour and unravel new physics. It is expected to find that quantum correlations fundamentally change: for example, correlated photons that should naturally bunch might anti-bunch, show a mixed bunching-antibunching, or even uncorrelated behaviour.
Partners: University of Vienna, University of Rostock
The age at which people have their children has increased tremendously since the 1970s in the low fertility countries. The reasons for delayed reproduction have been explored extensively, but very little attention has been given to the factors that facilitate and constrain fertility at later ages (from age 30). Yet, the desire and ability of those who did not have children in their 20s to have them later (“fertility recuperation”) is decisive for future fertility levels, and for life satisfaction among those who wish children. BIC.LATE will fill this gap by studying the biological, individual and contextual factors of later reproduction in the low-fertility countries, and possible catch-up behaviour of those who did not have a child earlier. In this new perspective, we will: 1) Measure the effect of biological limits on fertility recuperation with contemporary data for women and men, accounting for changes in Assisted Reproductive Technologies; 2) Identify the remaining individual factors of later fertility (demographic and socio-economic) among women and men, exploring factors more relevant at that ages (health, dedication to work); 3) Understand to what extent the structural and cultural context of a country (e.g. policies, economic situation, social norms) matters for fertility recuperation in a comparative perspective; 4) Estimate the link of these factors with fertility recuperation and draw cutting-edge meta-scenarios of cohort fertility. We will use data from social surveys (cross-sectional, panels) and aggregate cohort fertility data in Europe, the English-speaking oversea countries and East Asia, and data from a fertility clinic in Vienna. The research design includes survival analysis on panel data and on retrospective family history, aggregate correlations and cohort fertility projections. BIC.LATE will inform policy makers about the major contextual drivers of future fertility, using clearly articulated storylines and their associated scenarios.
Partners: University of Rostock, University of Southampton
The aim of BAPS is to develop a ground-breaking simulation model of international migration, based on a population of intelligent, cognitive agents, their social networks and institutions, all interacting with one another. The project will transform the study of migration – one of the most uncertain population processes and a top-priority EU policy area – by offering a step change in the way it can be understood, predicted and managed. In this way, BAPS will effectively integrate behavioural and social theory with modelling. To develop micro-foundations for migration studies, model design will follow cutting-edge developments in demography, statistics, cognitive psychology and computer science. BAPS will also offer a pioneering environment for applying the findings in practice through a bespoke modelling language. Bayesian statistical principles will be used to design innovative computer experiments, and learn about modelling the simulated individuals and the way they make decisions. In BAPS, we will collate available information for migration models; build and test the simulations by applying experimental design principles to enhance our knowledge of migration processes; collect information on the underpinning decision-making mechanisms through psychological experiments; and design software for implementing Bayesian agent-based models in practice. The project will use various information sources to build models bottom-up, filling an important epistemological gap in demography. BAPS will be carried out by the Allianz European Demographer 2015, recognised as a leader in the field for methodological innovation, directing an interdisciplinary team with expertise in demography, agent-based models, statistical analysis of uncertainty, meta-cognition, and computer simulations. The project will open up exciting research possibilities beyond demography, and will generate both academic and practical impact, offering methodological advice for policy-relevant simulations.