diatomic-py 2.1.0

A package for calculating rotational and hyperfine structure of singlet diatomic molecules.

Python package to calculate the hyperfine energy levels of singlet sigma diatomic molecules (e.g. RbCs, KCs and KRb) under various applied fields. The hyperfine structure can be calculated in static electric and magnetic fields and, when provided the polarisability, oscillating electric fields.

More detailed information can be found in the documentation at https://diatomic-py.readthedocs.io .

Diatomic-py is licensed under a BSD 3 clause license, a copy can be found here.

If you use our work for academic purposes you can cite us using:

J.A.Blackmore et al. Diatomic-py: A python module for calculating the rotational and hyperfine structure of \(^1\Sigma\) molecules, [Arxiv e-prints 2205.05686](https://arxiv.org/abs/2205.05686) (2022).

This work has continued to evolve since the release of the paper, and so the API is different.

PyPi Installation

python -m pip install diatomic-py

Manual Installation

Clone the repository:

git clone https://github.com/durham-qlm/diatomic-py.git
cd diatomic-py

It is recommended to then install the python package into virtual environment:

# You may need to substitute `python` for `python3` if you're on macOS
python -m venv ./venv
source ./venv/bin/activate
# After activating the virtual env you should only need `python`
python --version
which python

The below installation commands assume you are active in such an environment. You can then install the package, adding optional user-facing features with extras:

# Installs essentials only
python -m pip install .

# Installs essentials + plotting support
python -m pip install ".[plotting]"

# Installs plotting support and optional progress bars
python -m pip install ".[plotting,progress]"

Development dependencies are managed with dependency groups. With uv:

uv sync --group dev
uv run pre-commit install
uv run pytest

Example

import numpy as np
import matplotlib.pyplot as plt
import scipy.constants

from diatomic.systems import SingletSigmaMolecule
import diatomic.operators as operators
import diatomic.calculate as solver

GAUSS = 1e-4  # T
MHz = scipy.constants.h * 1e6

# Generate Molecule
mol = SingletSigmaMolecule.from_preset("Rb87Cs133")
mol.Nmax = 2

# Generate Hamiltonians
H0 = operators.hyperfine_ham(mol)
Hz = operators.zeeman_ham(mol)

# Parameter Space
B = np.linspace(0.001, 300, 50) * GAUSS

# Overall Hamiltonian
Htot = H0 + Hz * B[:, None, None]

# Solve (diagonalise) Hamiltonians
eigenenergies, eigenstates = solver.solve_system(Htot)

# Plot results
fig, (ax_up, ax_down) = plt.subplots(2, 1, sharex=True)

ax_down.plot(B / GAUSS, eigenenergies[:, 0:32] / MHz, c="k", lw=0.5, alpha=0.3)
ax_up.plot(B / GAUSS, eigenenergies[:, 32:128] / MHz, c="k", lw=0.5, alpha=0.3)

ax_down.set_xlabel("Magnetic Field (G)")
fig.supylabel("Energy / h (MHz)")

plt.show()

For more examples of usage, see the ./examples folder.