🌊 Quantum Fourier Transform

The quantum algorithm that transforms computation from time to frequency domain

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Shor's Factoring Algorithm

🎯 The Fourier Transform

The Fourier transform is one of the most important mathematical tools in science and engineering. It converts signals between time domain and frequency domain, revealing hidden patterns. The Quantum Fourier Transform (QFT) is its quantum analog—exponentially faster and the foundation of many quantum algorithms.

⚡ The Speed Advantage

Classical Fast Fourier Transform (FFT) needs O(N log N) operations for N data points. QFT needs only O((log N)²) quantum gates—an exponential speedup! For 1 million points, FFT needs ~20 million operations; QFT needs just ~400 gates.

256 points (N=256)
2,048
Classical FFT ops
QFT equivalent
36
Quantum gates
Speedup
57×
Faster!

🌟 Why It Matters

  • Core of Shor's Algorithm: QFT enables exponential speedup for integer factorization
  • Phase Estimation: Central component in quantum phase estimation protocol
  • Period Finding: Efficiently finds periods in modular arithmetic functions
  • Universal Tool: Used in quantum simulation, optimization, and machine learning

🔑 Key Concepts

📊

Frequency Basis

Transform from computational basis to frequency basis using phase rotations

🔄

Phase Encoding

Encode frequency information in quantum phases using controlled rotations

Quantum Parallelism

Process all frequencies simultaneously in superposition

🎵

Inverse QFT

Reverse transform returns from frequency to time domain