Quantum glossary

Hadamard gate

Also: h gate, hadamard

The single-qubit gate that turns |0⟩ into an equal superposition of |0⟩ and |1⟩, and back again.

Applying H twice returns the original state — the two paths to |1⟩ cancel. That small fact is interference in its simplest form, and the reason H is the first gate of almost every algorithm.

H|0⟩ = (|0⟩+|1⟩)/√2, H² = I