Recent Advances in Hilbert Spaces: Theoretical Innovations, Quantum Extensions, and Interdisciplinary Applications (2023–2026) (Vol-II)
Syed Muntasir Mamun
Abstract
While Hilbert spaces remain a cornerstone of functional analysis and quantum mechanics since their formalisation in the early 20th century, the period 2023–2026 has witnessed a surge of novel theoretical refinements, experimental validations, and cross-disciplinary integrations. This update builds directly upon the foundational treatment presented in the preceding paper, emphasising connections to quantum information geometry. Key developments include Hilbert space fragmentation in many-body systems (with experimental realisation), operator-theoretic breakthroughs (e.g., transfinite fixed points and Aluthge transforms), extensions of reproducing kernel Hilbert spaces (RKHS) to machine learning and Gaussian processes, computational advances in rigged Hilbert spaces for generalised eigenfunctions, and geometric reformulations in quantum gravity and holographic duality. We explore these from algebraic, geometric, analytic, and applied perspectives, addressing nuances such as infinite-dimensional subtleties, non-Hermitian extensions, and boundary-condition independence. Implications span quantum technologies, AI, and foundational physics, with rigorous links to the Fubini–Study/Bures metrics and quantum Fisher information. Edge cases (e.g., fragmented subspaces, evolving Hilbert spaces) and future directions are highlighted for completeness. Also available on Academia.edu: https://www.academia.edu/attachments/132280253/download_file?s=portfolio