qutip

QuTiP 5

Scope

Use QuTiP for finite-dimensional quantum mechanics, quantum optics, Lindblad dynamics, trajectories, weak-coupling Bloch-Redfield models, and specialized Floquet, HEOM, and permutational-invariance methods. It is not a hardware execution SDK. Circuit and control functionality moved to separate QuTiP family packages.

This skill targets QuTiP 5.3.0, released 2026-05-22. QuTiP 5.3 requires Python 3.11 or newer. Its required distributions are NumPy (>=1.23.2), SciPy (>=1.9.2, excluding 1.16.0 and 1.17.0), and packaging.

Reproducible uv snapshot

Create a dedicated environment and pin every direct distribution:

uv venv --python 3.11
uv pip install "qutip==5.3.0"

For plots:

uv pip install "qutip[graphics]==5.3.0"

Optional QuTiP family packages are independently versioned:

uv pip install "qutip-qip==0.4.2"
uv pip install "qutip-qtrl==0.2.0"
uv pip install "qutip-jax==0.1.1"

• qutip-qip 0.4.2 (2026-06-23) is the production/stable circuit, gate, and noisy-device simulation package. Import from qutip_qip, not qutip.qip.
• qutip-qtrl 0.2.0 (2026-06-23) provides GRAPE and CRAB quantum optimal control. It is not a trajectory viewer. Import from qutip_qtrl, not qutip.control; PyPI still classifies it pre-alpha.
• qutip-jax 0.1.1 (2025-05-29) is the official JAX data backend for GPU and automatic-differentiation experiments. It is explicitly pre-alpha.
• qutip-cupy is an official QuTiP-organization repository, but it has no PyPI release and its own README says it is not officially released. Do not put an unreleased Git install into a reproducible workflow.

Use a project lockfile or a hash-generating uv pip compile workflow when transitive dependency identity must also be frozen.

Non-negotiable model contract

Before solving, record:

1. Units and convention. QuTiP equations normally set (\hbar=1). Hamiltonian entries are angular frequencies and rates have reciprocal-time units. Convert cyclic frequency with (2\pi f); never mix Hz and rad/s.
2. Subsystem order. tensor(A, B, C) fixes subsystem indices 0, 1, 2. Preserve that order in every state, operator, collapse channel, and partial trace. obj.ptrace([0, 2]) keeps those subsystems; it does not trace them.
3. State validity. Check ket norm or density-matrix Hermiticity, unit trace, and eigenvalues above a stated negative tolerance. Tiny negative values may be numerical; material negativity invalidates a claimed state.
4. Generator meaning. A Lindblad channel with rate gamma is represented by sqrt(gamma) * A, not gamma * A. Define what each rate measures. For example, sqrt(gamma_phi / 2) * sigmaz() gives coherence decay exp(-gamma_phi * t).
5. Approximations. State rotating-wave, Born-Markov, secular, weak-coupling, bath-equilibrium, truncation, symmetry, and initial-factorization assumptions wherever used.
6. Numerics. Justify Hilbert truncation, output grid, integration method, tolerances, trajectory count, and random seeds. Report result.stats.
7. Convergence. Sweep every artificial cutoff: Fock dimension, time/frequency window and spacing, ODE tolerances, trajectories, Floquet harmonics, HEOM depth and bath exponents, or PIQS representation as applicable.