vqe-pennylane 0.3.13

Quantum Simulation Suite with VQE, QPE, and QITE modules (PennyLane-based)

Quantum Simulation Suite

PennyLane-based workflows for:

• ground-state VQE
• excited-state methods
• quantum phase estimation
• variational imaginary-time evolution
• variational real-time evolution

Implemented packages:

• vqe for ground-state and excited-state solvers
• qpe for phase-estimation workflows
• qite for projected variational dynamics (VarQITE, VarQRTE)
• common for shared chemistry, Hamiltonians, caching, and plotting

What This Repo Is Good For

Use this repo if you want:

• one Hamiltonian pipeline shared across VQE, QPE, and QITE/QRTE
• one shared problem-resolution layer for molecule, explicit-geometry, and expert-mode inputs
• reproducible runs with stable cache keys and JSON outputs
• both Python APIs and CLI workflows
• notebooks that separate demos from benchmarks

It is optimized for small-molecule algorithm development and comparison, not large-scale production chemistry.

Choose A Method

Use VQE when you want a ground-state energy or a good reference state.

Use ADAPT-VQE when you want an adaptive ansatz rather than a fixed one.

Use QSE, EOM-QSE, LR-VQE, or EOM-VQE when you already have a converged VQE reference and want excited-state information.

Use SSVQE or VQD when you want variational excited-state solvers directly.

Use QPE when you want spectral / phase information rather than a compact variational state.

Use VarQITE when you want imaginary-time relaxation toward a low-energy state.

Use VarQRTE when you already have a relevant state and want to evolve it in real time and analyze observables.

Use expert-mode Hamiltonian inputs when you want to benchmark algorithms on non-chemistry qubit models without going through the molecule / geometry pipeline.

Install

From PyPI:

pip install vqe-pennylane

From source:

git clone https://github.com/SidRichardsQuantum/Variational_Quantum_Eigensolver.git
cd Variational_Quantum_Eigensolver
pip install -e .

Verify:

python -c "import vqe, qpe, qite, common; print('Quantum stacks imported successfully')"

Quickstart

Python:

import pennylane as qml

from vqe import run_vqe
from qite import run_qite, run_qrte

vqe_res = run_vqe(molecule="H2")
print("VQE:", vqe_res["energy"])

qite_res = run_qite(molecule="H2", steps=75, dtau=0.2)
print("VarQITE:", qite_res["energy"])

qrte_res = run_qrte(molecule="H2", steps=20, dt=0.05)
print("VarQRTE final energy:", qrte_res["energy"])

H_model = qml.Hamiltonian([1.0, 0.5], [qml.PauliZ(0), qml.PauliX(0)])
model_res = run_vqe(
    hamiltonian=H_model,
    num_qubits=1,
    reference_state=[1],
    ansatz_name="RY-CZ",
    steps=10,
    plot=False,
)
print("Model VQE:", model_res["energy"])

run_vqe() uses the calibrated default stepsize for the selected optimizer when stepsize is omitted. The vqe CLI does the same when --stepsize is omitted.

CLI:

python -m vqe -m H2
python -m qpe --molecule H2 --ancillas 4 --shots 1000 --trotter-steps 2
python -m qite run --molecule H2 --steps 75 --dtau 0.2
python -m qite run-qrte --molecule H2 --steps 20 --dt 0.05

Typical Workflow

For stationary-state work:

1. run VQE to get a ground-state reference
2. run post-VQE or excited-state solvers if needed
3. compare against exact small-system references where possible

For dynamics:

1. prepare a state with VQE, VarQITE, or an excited-state workflow
2. use VarQRTE for real-time dynamics
3. benchmark against exact evolution on small systems when possible

Package Overview

vqe

Includes:

• run_vqe
• run_adapt_vqe
• run_lr_vqe
• run_eom_vqe
• run_qse
• run_eom_qse
• run_ssvqe
• run_vqd

Use it for:

• ground-state optimization
• excited-state studies
• ansatz / optimizer / mapping comparisons
• geometry scans
• noisy VQE experiments

qpe

Includes:

• run_qpe

Use it for:

• phase-to-energy estimation
• ancilla / shot studies
• controlled time-evolution experiments

Default QPE settings are H2-calibrated baseline defaults:

• n_ancilla=4
• t=1.0
• trotter_steps=2
• shots=1000

They are intended as good small-molecule starting values, not globally optimized settings for every molecule.

qite

Includes:

• run_qite
• run_qrte

Use it for:

• imaginary-time relaxation with VarQITE
• real-time dynamics with VarQRTE
• prepared-state quench workflows

Important:

• VarQITE is a state-finding / relaxation method
• VarQRTE is a dynamics method, not an eigensolver
• for time-independent Hamiltonians, VarQRTE should usually conserve energy up to numerical error

Shared Infrastructure

All solver packages use the same chemistry layer in common/.

That gives you:

• consistent Hamiltonians across algorithms
• comparable outputs across methods
• shared run signatures and cache reuse
• standardized result and image paths

Main shared modules:

• common/molecules.py
• common/geometry.py
• common/hamiltonian.py
• common/problem.py
• common/persist.py
• common/plotting.py
• common/paths.py

Non-Molecule Mode

The Python APIs also support a direct qubit-Hamiltonian mode for algorithm benchmarking outside chemistry.

Currently supported:

• run_vqe(..., hamiltonian=H, num_qubits=..., reference_state=...)
• run_qite(..., hamiltonian=H, num_qubits=..., reference_state=...)
• run_qrte(..., hamiltonian=H, num_qubits=..., reference_state=...)
• run_qpe(..., hamiltonian=H, hf_state=..., system_qubits=...)

Notes:

• this is a Python expert-mode API, not a CLI feature
• arbitrary qubit wire labels are normalized internally
• run_qpe(...) expert mode requires both hamiltonian and hf_state
• chemistry-specific ansatzes like UCCSD still require chemistry metadata; for generic model Hamiltonians prefer ansatzes like RY-CZ, Minimal, or StronglyEntanglingLayers

Outputs And Reproducibility

Generated outputs are written under:

results/vqe/
results/qpe/
results/qite/
images/vqe/
images/qpe/
images/qite/

General behavior:

• run configurations are hashed deterministically
• matching runs reuse cached JSON records
• --force recomputes instead of loading cache

For sampled QPE runs with finite shots, seed still matters because the measured bitstring distribution is stochastic. In analytic mode (shots=None), the seed is effectively irrelevant.

Notebooks

Notebook guide:

• notebooks/README_notebooks.md

Layout:

• notebooks/getting_started/ for usage-oriented demos
• notebooks/benchmarks/ for exact-reference, comparison, and scan workflows

Recommended starting points:

• notebooks/getting_started/01_vqe_vs_qpe_from_scratch_h2.ipynb
• notebooks/getting_started/07_getting_started_qite_h2.ipynb
• notebooks/getting_started/11_getting_started_qrte_h2.ipynb
• notebooks/benchmarks/qite/H2/Exact_QRTE_Benchmark.ipynb

Documentation

Use these in order:

1. README.md for orientation and quickstart
2. USAGE.md for CLI and Python entrypoints
3. THEORY.md for algorithmic background
4. notebooks/README_notebooks.md for notebook navigation

Deeper implementation notes:

• more_docs/architecture.md
• more_docs/vqe/
• more_docs/qpe/
• more_docs/qite/

Repository Layout

Variational_Quantum_Eigensolver/
├── vqe/
├── qpe/
├── qite/
├── common/
├── notebooks/
│   ├── getting_started/
│   └── benchmarks/
├── results/
├── images/
├── README.md
├── USAGE.md
├── THEORY.md
└── pyproject.toml

Testing

pytest -q

Author

Sid Richards

• LinkedIn: sid-richards-21374b30b
• GitHub: SidRichardsQuantum

License

MIT. See LICENSE.