circuits / quantum-phase-estimation

Quantum Phase Estimation (2+1)

✓FEATURED

Estimates the phase θ in U|ψ⟩ = e^{2πiθ}|ψ⟩ using 2 counting qubits and inverse QFT.

quantumcomputer.dev
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1OPENQASM 2.0;
2include "qelib1.inc";
3qreg q[3];
4creg c[2];
5// Eigenstate
6x q[2];
7// Hadamard counting qubits
8h q[0]; h q[1];
9// Controlled-U
10cp(pi/2) q[1],q[2];
11cp(pi) q[0],q[2];
12// Inverse QFT
13h q[0];
14cp(-pi/2) q[1],q[0];
15h q[1];
16swap q[0],q[1];
17measure q[0] -> c[0];
18measure q[1] -> c[1];

Cite this circuit

MIT
quantumcomputer.dev. "Quantum Phase Estimation (2+1)". quantumcomputer.dev/circuits/quantum-phase-estimation. 2026.