Ground State and Entanglement Transitions in a Disordered Ising–Heisenberg Spin Chain

We numerically study the ground‐state energy and entanglement structure of a disordered spin chain interpolating between the classical Ising antiferromagnet and the quantum Heisenberg antiferromagnet. The model consists of an Ising chain, where the quantum exchange terms are activated on each bond with probability . Using density matrix renormalization group (DMRG) simulations with ITensor for system sizes up to and over 10 000 disorder realizations for each value, we extract the dependence of the ground‐state energy and the associated entanglement entropy as functions of . We find a smooth crossover between the classical and quantum regimes, with a notable peak in the entanglement fluctuations around . Statistical analysis of entanglement distributions reveals a bimodality transition that provides additional evidence for a percolation‐like crossover.