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The Journal of Open Source Software

Sunny.jl: A Julia Package for Spin Dynamics

David Dahlbom, Hao Zhang, Cole Miles, Sam Quinn, Alin Niraula, Bhushan Thipe, Matthew S. Wilson, Sakib Matin, Het Mankad, Steven Hahn, Daniel M. Pajerowski, Steven Johnston, Zhentao Wang, Harry Lane, Ying Wai Li, Xiaojian Bai, Martin Mourigal, Cristian D. Batista, Kipton M. Barros

Published Dec 20, 2025• 20 citations
Publisher

Abstract

Sunny is a Julia package designed to serve the needs of the quantum magnetism community.It supports the specification of a very broad class of spin models and a diverse suite of numerical solvers.These include powerful methods for simulating spin dynamics both in and out of equilibrium.Uniquely, it features a broad generalization of classical and semiclassical approaches to SU(N) coherent states, which is useful for studying systems exhibiting strong spin-orbit coupling or local entanglement effects.Sunny also offers a well-developed framework for calculating the dynamical spin structure factor, enabling direct comparison with scattering experiments.Ease of use is a priority, with tools for symmetry-guided modeling and interactive visualization.

DOI
10.21105/joss.08138

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Sunny is a Julia package designed to serve the needs of the quantum magnetism community.It supports the specification of a very broad class of spin models and a diverse suite of numerical solvers.These include powerful methods for simulating spin dynamics both in and out of equilibrium.Uniquely, it features a broad generalization of classical and semiclassical approaches to SU(N) coherent states, which is useful for studying systems exhibiting strong spin-orbit coupling or local entanglement effects.Sunny also offers a well-developed framework for calculating the dynamical spin structure factor, enabling direct comparison with scattering experiments.Ease of use is a priority, with tools for symmetry-guided modeling and interactive visualization.
Sunny is a Julia package designed to serve the needs of the quantum magnetism community. It supports the specification of a very broad class of spin models and a diverse suite of numerical solvers. These include powerful methods for simulating spin dynamics both in and out of equilibrium. Uniquely, it features a broad generalization of classical and semiclassical approaches to SU(N) coherent states, which is useful for studying systems exhibiting strong spin-orbit coupling or local entanglement effects. Sunny also offers a well-developed framework for calculating the dynamical spin structure factor, enabling direct comparison with scattering experiments. Ease of use is a priority, with tools for symmetry-guided modeling and interactive visualization.
SpiDy.jl solves the non-Markovian stochastic dynamics of interacting classical spin vectors and harmonic oscillator networks in contact with a dissipative environment. The methods implemented allow the user to include arbitrary memory effects and colored quantum noise spectra. In this way, SpiDy.jl provides key tools for the simulation of classical and quantum open systems including non-Markovian effects and arbitrarily strong coupling to the environment. Among the wide range of applications, some examples range from atomistic spin dynamics to ultrafast magnetism and the study of anisotropic materials. We provide the user with Julia notebooks to guide them through the various mathematical methods and help them quickly set up complex simulations.
We present PEPSKit...jl, a Julia package for simulating two-dimensional quantum many-body systems with infinite projected entangled-pair states (iPEPS). PEPSKit...jl builds on the TensorKit...jl package for tensor computations and provides high-level algorithms for iPEPS simulations that support both Abelian and non-Abelian symmetries, as well as fermionic systems. This work gives an overview of the main package features, which include support for ground-state, time-evolution, and finite-temperature simulations in systems with different physical symmetries and lattice geometries. These capabilities are illustrated through various examples and technical benchmarks.
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Few-body physics explores quantum systems of a small number of particles, bridging the gap between single-particle and many-body regimes. To provide an accessible tool for such studies, we present FewBodyToolkit.jl, a Julia package for quantum few-body simulations. The package supports general two- and three-body systems in various spatial dimensions with arbitrary pair-interactions, and allows to calculate bound and resonant states. The implementation is based on the well-established Gaussian expansion method and we illustrate the package’s capabilities through benchmarks and research examples. The package comes with documentation and examples, making it useful for research, teaching, benchmarking, and method development.