vqe

Estimate ground-state energies for 2-qubit Ising Hamiltonians using VQE with COBYLA.

30|2|Updated Apr 16, 2026
One-click install
npx skills add https://github.com/unitarylab/quantum-skills --skill vqe
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: vqe
Source: https://github.com/unitarylab/quantum-skills/tree/main/algorithms/quantum-machine-learning/vqe
Command: npx skills add https://github.com/unitarylab/quantum-skills --skill vqe

SYSTEM DOCUMENTATION & REQUIREMENTS

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

What problem does it solve?

Serves as a practical pathway to estimate ground-state energies for small quantum systems using a variational quantum eigensolver (VQE) in a 2-qubit Ising model.

Core Features & Use Cases

  • Hybrid quantum-classical optimization using COBYLA to minimize energy.
  • Exact energy comparison and circuit visualization for educational exploration.
  • Run-ready demonstrations with a simple 2-qubit Ising Hamiltonian.
  • Use Case: Demonstrate VQE workflows and compare approximate results to exact spectra.

Quick Start

Execute the example script to run a VQE on the 2-qubit Ising model.

Frequently Asked Questions about vqe

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

FAQPage Schema
How do I estimate ground-state energy for a 2-qubit Ising model using VQE?▼

VQE estimates ground-state energies by running a hybrid quantum-classical loop. A parameterized quantum circuit prepares a trial state, and a classical optimizer like COBYLA adjusts parameters to minimize the measured energy expectation value until convergence.

How does variational quantum eigensolver optimization work for small Hamiltonians?▼

Variational quantum eigensolver optimization for small Hamiltonians works by combining a quantum circuit simulator with the COBYLA optimizer. It uses an Ry+CX ansatz to prepare trial states and evaluates statevectors to minimize energy for educational demonstrations.

Can I use COBYLA for quantum circuit simulation and ansatz design?▼

Yes, you can use COBYLA to optimize ansatz parameters in a quantum circuit simulation. This Skill specifically uses COBYLA to minimize energy expectation values derived from an Ry+CX ansatz evaluated via statevector simulation.

What is the best way to compare approximate VQE results to exact energy spectra?▼

The best way to compare approximate VQE results to exact spectra is to run a small Hamiltonian simulation that outputs both values. This Skill calculates exact ground-state energies alongside VQE optimization results for direct comparison.

Do I need a quantum circuit simulator to run variational quantum eigensolver demonstrations?▼

Yes, running VQE demonstrations requires a quantum circuit simulator to evaluate the ansatz statevector. This Skill depends on a simulator backend to compute energy expectation values for the Hamiltonian during the optimization loop.

When should I not use a variational quantum eigensolver for quantum computing?▼

You should not use VQE for large-scale Hamiltonians or systems requiring deep circuits, as the Ry+CX ansatz and COBYLA optimizer here are tailored for small 2-qubit Ising models. It is intended for educational demos, not large-scale research simulations.