Exact Positive-P Simulation of Open Quantum Spin Systems with Generalized Density Matrix Formalism

arXiv:2610.38059v1 Announce Type: new Abstract: The positive-P representation for bosons allows scalable exact simulations of many-body open quantum systems, provided dissipation is strong enough to stabilise stochastic trajectories. Designing analogous methods for spin systems, relevant to quantum technologies, remains challenging, as previous spin positive-P formulations can exhibit systematic errors even when simulations are numerically stable. Here, we develop a phase-space representation that maps spin-$\frac{1}{2}$ degrees of freedom onto parameters of a local generalized density matrix (GDM), rather than SU(2) coherent states.