Read the circuit for the QFT on 2 qubits and reverse and dagger everything

$$ (1 \otimes H)(Controlled(2,S_1^\dagger))(H \otimes 1) $$

Edit:

For how: Implementation of inverse QFT?

This decomposition is $m=2$ on https://en.wikipedia.org/wiki/Quantum_Fourier_transform Note that $R_2 = S$

$1 \otimes H$ to denote Hadamard on the second qubit. $H \otimes 1$ for Hadamard on the first. $Controlled(2,S_1)$ for use qubit 2 as the control and assuming that apply $S$ on the first qubit.

Read the circuit for the QFT on 2 qubits and reverse and dagger everything

$$ (1 \otimes H)(Controlled(2,S_1^\dagger))(H \otimes 1) $$

Edit:

For how: Implementation of inverse QFT?

This decomposition is $m=2$ on https://en.wikipedia.org/wiki/Quantum_Fourier_transform Note that $R_2 = S$

$1 \otimes H$ to denote Hadamard on the second qubit. $H \otimes 1$ for Hadamard on the first. $Controlled(2,S_1^\dagger)$ for use qubit 2 as the control and assuming that apply $S^\dagger$ on the first qubit.

Read the circuit for the QFT on 2 qubits and reverse and dagger everything

$$ (1 \otimes H)(Controlled(2,S_1))(H \otimes 1) $$

Read the circuit for the QFT on 2 qubits and reverse and dagger everything

$$ (1 \otimes H)(Controlled(2,S_1^\dagger))(H \otimes 1) $$

Edit:

For how: Implementation of inverse QFT?

This decomposition is $m=2$ on https://en.wikipedia.org/wiki/Quantum_Fourier_transform Note that $R_2 = S$

$1 \otimes H$ to denote Hadamard on the second qubit. $H \otimes 1$ for Hadamard on the first. $Controlled(2,S_1)$ for use qubit 2 as the control and assuming that apply $S$ on the first qubit.