Driven-dissipative spin systems: semiclassical approximations and beyond
Zeijan Li (Paris Cité)
The investigation of open quantum many-body systems is usually hindered by the “curse of dimensionality” and requires appropriately designed approximation tools. In the context of spin systems, I will first introduce a semiclassical framework for solving open quantum dynamics [1,2]. The method consists of generalized spin-wave approximations applied to quantum trajectories unraveled from the Lindblad master equation, and generally applies to regimes beyond the reach of conventional spin-wave theories, including short-range interactions and local quantum jumps, enabling the efficient simulation of large-scale interacting spins. I will demonstrate the approach by considering a variable-range driven-dissipative Ising model on a 2D lattice, and show that the interaction range alters the universality class of the criticality in a Z2 symmetry breaking dissipative phase transition. I will then discuss how this semiclassical description can be naturally “upgraded” to capture the exact Lindblad dynamics via a multi-configuration ansatz in the framework of time-dependent variational principle [3], where the equation of motion can be assembled analytically (without any need for Monte-Carlo sampling like neural-network methods do) and efficiently solved. Finally (if time permits), I will introduce the extension of the above multi-configuration variational approach to the regime of stochastic quantum trajectories.
[1] ZL, A Delmonte, R Fazio, PRB 113, 214324 (2026)
[2] ZL, A Delmonte, X Turkeshi, R Fazio, Nat. Commun. 16, 4329 (2025)
[3] J Tosca*, ZL*, et al, arXiv:2604.01165 (2026)