= Controlled quantum gate
{{wiki=Quantum_logic_gate#Controlled_gates}}
<Controlled quantum gates> are gates that have two types of input qubits:
* control <qubits>
* operand <qubits> (terminology made up by <Ciro Santilli> just now)
These gates can be understood as doing a certain <unitary operation> only if the control qubits are enabled or disabled.
The first example to look at is the <CNOT gate>.
\Image[https://upload.wikimedia.org/wikipedia/commons/d/dc/Controlled_gate.svg]
{title=Generic <controlled quantum gate> symbol}
{description=
The black dot means "control qubit", and "U" means an arbitrary <Unitary operation>.
When the operand has a conventional symbol, e.g. the <image Quantum NOT gate symbol> for the <quantum NOT gate> to form the <CNOT gate>, that symbol is used in the operand instead.
}