Bloch Sphere Demo

The Bloch Sphere demo is an interactive visualization tool that helps users understand how quantum gates affect single-qubit states on the Bloch sphere.

Overview

The Bloch sphere is a geometrical representation of a pure quantum state of a 2-level quantum system (qubit). This demo provides an intuitive way to explore quantum gates and their effects on single-qubit states through visual feedback in your web browser.

Note: The Bloch sphere representation is only applicable to single qubits. For multi-qubit systems, other visualization methods are needed.

Demo Interface

The Grok Bloch demo provides an interactive web interface where you can:

  • View the Bloch sphere representation in 3D
  • See the current quantum state equation at the top
  • Click gate buttons (X, Y, Z, S, T, H, etc.) to apply transformations
  • Choose rotation angles (θ=π/8 or θ=π/12) for rotation gates
  • Watch the Bloch vector move in real-time
  • Monitor the probability of measuring |0⟩

Grok Bloch Demo Interface The interactive Grok Bloch interface showing the Bloch sphere, quantum state, and gate controls

Features

  • Interactive Visualization: See how quantum gates transform qubit states in real-time
  • Educational Tool: Perfect for understanding fundamental single-qubit quantum concepts
  • Web-Based Interface: Runs in your browser for easy access
  • Gate Operations: Apply common quantum gates (Pauli-X, Y, Z, Hadamard, rotations)
  • Real-Time Updates: Watch the Bloch vector move as you apply gates

What You'll Learn

  • Quantum State Representation: How single qubits are represented on the Bloch sphere
  • Gate Operations: Visual understanding of how gates transform states
  • Superposition: See how qubits exist in multiple states simultaneously
  • Phase: Understand the role of quantum phase in single-qubit operations

Running the Demo

Preferred Method: Desktop Icon

  1. Look for the "Grok Bloch" icon on your RasQberry desktop
  2. Double-click to launch the demo
  3. Your default web browser will open with the interactive visualization

Alternative: Desktop Menu

  1. Click on the desktop menu
  2. Navigate to: Applications → RasQberry → Grok Bloch
  3. The demo will launch in your browser

Command Line (Advanced)

cd ~/RasQberry-Two source venv/RQB2/bin/activate cd demos/grok-bloch python3 grok_bloch.py

Understanding the Visualization

The Bloch sphere represents a single qubit's state as a point on a unit sphere:

  • North Pole (top): |0⟩ state
  • South Pole (bottom): |1⟩ state
  • Equator: Superposition states with equal probabilities
  • X-axis: |+⟩ and |-⟩ states (Hadamard basis)
  • Y-axis: |+i⟩ and |-i⟩ states (circular basis)

Any point on the sphere represents a valid pure quantum state of a single qubit.

Quantum Gates Demonstrated

Pauli Gates

  • X Gate (NOT gate): Rotates around X-axis by π (flips |0⟩ ↔ |1⟩)
  • Y Gate: Rotates around Y-axis by π
  • Z Gate (Phase flip): Rotates around Z-axis by π (adds phase)

Hadamard Gate

Creates equal superposition: transforms |0⟩ to (|0⟩ + |1⟩)/√2

Rotation Gates

  • Rx(θ): Rotation around X-axis by angle θ
  • Ry(θ): Rotation around Y-axis by angle θ
  • Rz(θ): Rotation around Z-axis by angle θ

Hardware Requirements

  • Raspberry Pi (Pi 5 recommended, Pi 4 supported)
  • Display (monitor or VNC connection)
  • Web browser (Chromium included in RasQberry)
  • Mouse/keyboard or touchscreen for interaction

Tips

  • Start Simple: Begin with basic gates (X, Z, H) before trying rotation gates
  • Observe Patterns: Notice how different gates affect the Bloch vector direction
  • Combine Gates: Apply multiple gates sequentially to see composite effects
  • Reset State: Use the reset button to return to |0⟩ state
  • Experiment: Try to reach specific target states by combining gates

Educational Context

This demo is excellent for:

  • Introduction to Quantum Computing: First visualization of quantum states
  • University Courses: Teaching quantum mechanics and single-qubit operations
  • Workshops: Interactive demonstrations at quantum computing events
  • Self-Learning: Exploring quantum concepts at your own pace
  • Gate Intuition: Building mental models for quantum gate operations

Limitations

  • Single Qubit Only: The Bloch sphere cannot represent multi-qubit states or entanglement
  • Pure States: Only represents pure states, not mixed states (density matrices)
  • Classical Visualization: A classical 3D visualization of quantum phenomena

Credits

Developed by James Weaver (JavaFXpert)

Learn More

IBM Quantum Resources

Qiskit Documentation

General Resources

Troubleshooting

Demo won't start

  • Ensure virtual environment is activated
  • Check that dependencies are installed: pip list | grep qiskit
  • Verify Python version: python3 --version (should be 3.9+)

Browser doesn't open

  • Open manually and navigate to: http://localhost:5000
  • Check firewall settings
  • Try a different browser (Firefox, Chromium)

Visualization not loading

  • Check console for errors (F12 in browser)
  • Ensure Python server is running in the background
  • Restart the demo
  • Check that no other service is using port 5000

Port already in use

# Find and kill process using port 5000 lsof -ti:5000 | xargs kill -9

Related Demos

IBM Quantum and Qiskit are trademarks of IBM Corporation. This demo uses open-source Qiskit software.

Edit this page on GitHub