OpenQuantumSystems.jl

OpenQuantumSystems.jl is a numerical framework written in Julia for simulating open quantum systems, with a focus on quantum biology and molecular aggregates in a finite basis. It is inspired by quantarhei and QuantumOptics.jl.

Features

Aggregate construction — Build Hamiltonians for aggregates of molecules with vibrational modes modelled as displaced harmonic oscillators.
Multiple solvers — Liouville-von Neumann, exact QME, Redfield, ansatz-based QME, iterative QME, and a unified solve() entry point.
Förster theory — Absorption/emission spectra, spectral overlap, and Förster excitation energy transfer rates.
Modified Redfield theory — Exciton basis transformation, lineshape functions, and population transfer rates beyond the weak-coupling limit.
Dipole couplings — Compute electronic couplings from molecular positions and transition dipole vectors.
Bath tracing — Trace over bath degrees of freedom using Franck-Condon factors.
Initial states — Thermal states and ultrafast laser excitation.
Post-processing — Picture conversion, validation, scoring, and comparison tools.
Convenience constructors — setup_dimer, setup_trimer, setup_linear_chain for quick prototyping.

Installation

pkg> add OpenQuantumSystems

using Pkg; Pkg.add("OpenQuantumSystems")

Quick Start

using OpenQuantumSystems

# Set up a dimer with one vibrational mode per molecule
agg = setup_dimer(E1=12500.0, E2=12700.0, J=100.0)

# Initial thermal state with laser excitation
W0 = thermal_state_composite(300.0, [0.0, 0.5, 0.5], agg)

# Time grid
tspan = get_tspan(0.0, 0.5, 500)

# Solve with QME ansatz
result = solve(W0, tspan, agg; method=:qme_ansatz)

See the Hamiltonian & Bath Model for the underlying theory, the Solver Selection Guide for choosing the right solver, and the Dimer examples tutorial for worked examples.