pauli

Approximate target quantum states by fitting fixed Pauli-word rotation sequences with L-BFGS-B optimization.

18|3|Updated Aug 14, 2026
One-click install
npx skills add https://github.com/unitarylab/quantum-practices --skill pauli-unitarylab
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: pauli
Source: https://github.com/unitarylab/quantum-practices/tree/main/algorithms/state-preparation/pauli
Command: npx skills add https://github.com/unitarylab/quantum-practices --skill pauli-unitarylab

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill requires numpy, scipy, unitarylab, and includes scripts (resource) components.

What problem does it solve? Preparing an arbitrary target quantum state on a quantum circuit requires choosing a gate sequence and its parameters; this Skill fits the angles of a fixed Pauli-word rotation ansatz so the emitted circuit reproduces a given target state vector within a requested error tolerance. ## Core Features & Use Cases - Variational State Preparation: Fits one rotation angle per Pauli word using deterministic multi-start L-BFGS-B optimization of the infidelity objective with parameter-shift gradients. - Circuit Emission and Validation: Emits the flattened Pauli-rotation circuit, extracts the prepared state from its dense matrix, and reports a global-phase-invariant L2 error with an ok/failed status. - Debugging and Reimplementation Guidance: Documents the exact ansatz ordering, optimizer settings, return contract, and a minimal manual implementation decomposing rotations into H, P, CX, RZ, and S gates. - Use Case: Given a one-qubit target state like [1, 1j]/sqrt(2), run PauliAlgorithm to obtain fitted weights, the prepared state, and a total error below 1e-6 for use in downstream quantum algorithm workflows. ## Quick Start Ask the assistant to run the Pauli state-preparation algorithm on a normalized one-qubit target vector with target_qubits=1 and target_error=1e-6, then report the status, fitted weights, and total error.

Frequently Asked Questions about pauli

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I prepare an arbitrary quantum state with Pauli rotations in Python?

Call PauliAlgorithm().run with your target vector Psi, target_qubits, and target_error. The algorithm fits one angle per Pauli word via L-BFGS-B optimization of infidelity and returns the prepared state, weights, circuit, and a phase-invariant total error.

What is the Pauli-word ansatz used for state preparation?

It is a fixed ordered sequence of Pauli words generated recursively, matching PennyLane's ArbitraryStatePreparation. Each word P contributes a rotation exp(-i*theta*P/2), and the ordered product of these rotations maps |0...0> to the target state.

Why does the Pauli state preparation return status failed?

A failed status means the best candidate's phase-invariant L2 error exceeded max(target_error, 1e-10), which can happen when the fixed ansatz lacks expressibility or the optimizer does not converge. It is a normal numerical outcome, not an exception.

What dependencies does the Pauli state preparation algorithm require?

It requires numpy, scipy, and the UnitaryLab library, specifically state_preparation_pauli_words, pauli_string_to_matrix, and pauli_state_preparation_circuit from unitarylab.library.pauli_operator. Missing helpers cause import failure before execution.

What are the limitations of variational Pauli-word state preparation?

The method uses dense matrices, so memory and compute grow exponentially with qubit count, limiting practical use to small registers. Convergence is not guaranteed for every target, and infidelity, candidate-selection error, and final total error are distinct quantities.