This record presents the quantum-theoretical component of the thickness‑structure hypothesis, an original physical framework developed by the author (ab_ab). The thickness‑structure hypothesis models physical reality as a continuous substrate characterized by a thickness field ϕ. The spatial extension, localization, and dynamical behavior of physical systems arise from structural variations in this field. Two structural variables define the state of the substrate:• thickness deviation Δf — the local structural alternative that determines potential localization sites • thickness fluctuation γT — the spatial spread of the structure responsible for wave-like behavior Depending on the combination of Δf and γT, the system exhibits three phases:• Wave phase (large γT) • Composite phase (intermediate γT) • Stable phase (γT below a critical threshold) Measurement is interpreted as a constraining operation that reduces γT, and the transition from wave-like to particle-like behavior is described as a structural phase transition satisfying γT ≤ γcrit(Δf). This document focuses specifically on the quantum aspects of the framework, including:• wave–particle duality as a phase-structural phenomenon • measurement-induced localization as a continuous transition • interference and tunneling as geometric consequences of the thickness field • entanglement as multi-region constraint coupling in γT • predictions such as continuous visibility change under partial measurement The purpose of this release is to establish a citable, timestamped reference for the quantum sector of the thickness‑structure hypothesis. All terminology, definitions, and conceptual structures introduced here originate with the author. License: CC BY 4.0 only. Thickness Structure Hypothesishttps://zenodo.org/records/18472696