Abstract
This study derives the unitary dynamics of a four qubit Heisenberg XXX chain with tunable next nearest neighbor coupling α, starting from a Bell type initial state, and analyzes the evolution of quantum resources under the phase φ = (α + 1)t. We provide closed form expressions for fidelity F(ρ(0),ρ(t)), coherence C_l₁(ρ(t)), and two qubit entanglement of formation E_F(t) for subsystems 12 and 34, all of which are governed by φ. Fidelity exhibits periodic behavior with F = cos(φ/2) and a frozen regime at α = -1 where F ≡ 1. Coherence follows C_l₁(ρ(t)) = sin²(φ/2), showing increasing sensitivity with α + 1 and vanishing at α = -1. Entanglement of formation E_F(t) is an entropic function of φ, displaying banded oscillations and freezing at α = -1. The phase φ unifies the behavior of all diagnostics, linking faster dynamics to larger α + 1 and revealing maximal sensitivity at (α + 1)t = π/4 + kπ/2. This integrated framework provides exact benchmarks for small quantum devices and a clear pathway to noise, finite temperature, and larger system extensions.