# Quantum fourier transform

To be able to understand more elaborate and powerful algorithms, we need to review and be able to identify routines that play important roles.

In this section you will learn about the Quantum fourier transform (QFT), a quantum analog to the classical discrete fourier transform that works over the amplitudes of the wavefunction.

The Quantum fourier transform is a subroutine in algorithms such like Shor's algorithm and Quantum phase estimation. In this video, QFT is presented in a rather visual representation to get more intuition on what QFT actually does. It contains an explanation of QFT for 2 qubits by María Flors Mor Ruiz and Elsie Loukiantchenko, Applied Physics MSc students at TU Delft.

## Prerequisite knowledge

- Fundamentals of quantum information
- Classical fourier transform

## Further thinking

How would the circuit look like for only 1 qubit?

In the 2 qubits system, what would be the result of the following expression? QFT(|0> + |2>)

## Further reading

- Nielsen and Chuang - Quantum Computation and Information (Chapter 5)
- N. David Mermin - Quantum Computer Science (Chapter 3.5)