QuaDLib

Quantum Dynamics Library for Research, Development and Education.

QuaDLib is a pure-Python library for quantum dynamics, built on NumPy and SciPy. It serves as a test bed for methods development and as a teaching tool; the tree-tensor-network (ML-MCTDH) methods it is meant to host are not implemented yet.

What works

• Primitive bases: sine, exponential and harmonic-oscillator DVRs (Sindvr, Expdvr, HOdvr), boson, spin-1/2, angular momentum and discrete bases (Boson, Spin, Jbasis, Discrete).
• Sum-of-products operators (SOP), with their full dense or sparse matrix representation.
• Numerically exact propagation of a full wavefunction tensor (WfnExact, quadlib.propagation.propagate_exact), either by integrating the TDSE with the SOP right-hand side (solver='zvode') or with scipy.sparse.linalg.expm_multiply on the sparse Hamiltonian matrix (solver='expm'). The second is faster and exact to machine precision as long as the sparse matrix fits in memory; operators with dense matrices on several degrees of freedom in one term favour the first.
• CPD wavefunctions (WfnCPD): norm, overlaps, reduced densities, expectation values, and propagation of the coefficient vector with frozen single-particle functions (propagate_cpd_A).
• Bath discretization of spectral densities (quadlib.tools.bath), correlation-function spectra and Fourier transforms (quadlib.tools.spectra).
• Reading the autocorrelation function of an existing Heidelberg MCTDH run directory (Rundirectory).

Experimental

quadlib.experimental holds unfinished or known-incorrect code and is not imported by quadlib: the tree data structures (Node, Tree, Pdof), placeholders for the MCTDH equations of motion, and the coupled CPD equations of motion. quadlib.legacy keeps older utilities that the library does not use.

Installation

Python 3.10 or later. NumPy and SciPy are the only required dependencies.

pip install quadlib

Extras:

pip install "quadlib[plot]"      # matplotlib, for the plotting helpers
pip install "quadlib[jupyter]"   # JupyterLab and jupytext, for the notebooks

From source:

git clone https://gitlab.com/tc-heidelberg/quadlib.git
cd quadlib
pip install -e ".[plot,dev]"     # dev adds pytest and ruff

or a specific release without cloning:

pip install git+https://gitlab.com/tc-heidelberg/quadlib.git@v0.1.0

Tests and examples

pytest               # fast tests
pytest -m slow       # long reference tests (about one minute)
ruff check           # linter

Worked examples are in docs/notebooks (jupytext format): spin_boson_example.py (exact propagation of a spin-boson model), td-cpd_example.md (CPD wavefunction), and bath_tests.md (bath discretization).

Development

Day-to-day development happens in a private repository within the group. This repository carries tagged releases, so its history is one commit per release rather than a record of development. Bug reports and questions are welcome through the issue tracker.

Authors

• Oriol Vendrell, oriol.vendrell@uni-heidelberg.de, ORCID 0000-0003-4629-414X
• Sudip Sasmal, sudipsasmal.chem@gmail.com

MIT License. See CITATION.cff for how to cite.