This project explores strong-gravity phenomena involving black holes in the context of high-energy physics applications and astrophysical observations including gravitational waves. The proposed studies can be loosely classified into four groups with considerable overlap. (i) Fundamental fields in strong gravity. Fundamental fields coupled to curvature are essential for cosmological models, for explaining the nature of dark matter or to extend the Standard Model of particle physics. In addition, scalar fields are often used as proxy for other, more complex interactions. Through numerical, perturbative and analytical modeling, we will explore the dynamics and wave emission of neutron stars and black holes in dark-matter environments and infer bounds on axion-like particles. (ii) Stability of black holes. The physical stability of black-hole solutions with or without the presence of fundamental matter fields will be studied. Such solutions represent possible end states of the dynamical processes and their importance critically relies on whether they form long-term stable spacetimes. (iii) Modified theories of gravity. Modifications and extensions of general relativity are being explored for a variety of reasons ranging from cosmological observations to attempts to unify general relativity with quantum mechanics. We will explore observable effects of various such theories in astrophysical systems with a particular focus on gravitational-wave and electromagnetic signatures, that could allow us to test general relativity against modified theories of gravity. (iv) High-energy collisions. The gravitational interaction of ultrarelativistic collisions will be modeled numerically and perturbatively to probe the possibility of black-hole formation in the framework of TeV gravity scenarios.

QLASS brings together experts from top research groups, up-and-coming SMEs, and industry to achieve the ambitious goal of producing a quantum photonic integrated circuit (QPIC) utilizing the extremely versatile technique of femtosecond laser writing (FLW) to fabricate 3D waveguides within glass developed for optimum photonic performance to support an unprecedented 200 reconfigurable optical modes. Compared to other QPIC techniques, glass yields extremely small interface losses (<5%) – ideal for modular, scalable architectures connecting multiple chips – with speed, affordability, and optimization for end-user goals. Incorporating high-performance single-photon sources, superconducting nanowire single-photon detectors, and electronics enabling reconfigurable state manipulation via control of an exceptionally large number of cryogenic-detector channels (200) and phase shifters (1000), we will create an end-to-end quantum photonics platform. We will implement Variational Quantum Algorithms (VQAs), leading candidates for near-term advantage, for which our platform is ideally suited. We will develop software for end users to translate their VQAs into FLW circuits, with error mitigation to enhance QPIC performance. Our principal use case is solving problems in the design of lithium-ion batteries to achieve improvements in capacity and efficiency crucial for attaining EU technological and sustainability goals. QLASS will attain substantial advancement both towards the specific QPIC objectives as well as glass development, with associated novel SNSPD processes, benefitting the wider community and enabling new quantum devices with performance far exceeding other platforms. Our combination of world-class experimentalists and theorists have the complementary expertise to successfully carry out the ambitious project objectives advancing practical QPICs.