Generalized phase-space techniques in mixed-(1/2, S) Heisenberg models: Wigner negativity and Rényi entropy

Abstract

Abstract Quantum phases in low-dimensional mixed-spin systems continue to attract significant interest due to their rich correlation structure and relevance to modern quantum technologies. Here, we investigate the one-dimensional mixed spin-(1/2, S ) Heisenberg model in an external magnetic field using a phase-space formulation based on the generalized Wigner function. Focusing on mixed-spin (1/2, 1) and (1/2, 3/2) systems, we show that phase-space indicators, including Rényi entropies and Wigner negativity, provide a complementary characterization of quantum phases and correlations, consistent with phase structures obtained from conventional observables. Our analysis reveals three robust regions in the phase diagram: ferrimagnetic, quantum–spin–liquid-like, and fully polarized. Ground-state level crossings emerge near the corresponding boundaries, marking finite-size precursors of thermodynamic phase transitions. By combining phase-space diagnostics with finite-size scaling, we identify how quantum correlations evolve toward the thermodynamic limit. These results deepen the understanding of correlation-driven phases in mixed-spin chains and establish phase-space methods as powerful tools for analyzing complex quantum magnetic systems.