Multi-Qubit Gates

Controlled operations

Controlled operations are the most basic way in which two qubits can interact with each other. Basically, a gate is applied to one qubit based on the current state of the other qubit. The operation can be anything like the X, Y, Z gates. Let’s try to understand with the help of an example.

CNOT gate

This is the controlled-NOT gate. It is a two-qubit gate. It performs a bit flip operation on the target qubit only when the control qubit is $|1\rangle$. This is quite similar to the XOR gate from classical computing.

Now, what are target and control qubits? We’ll have to understand this by ...

The control qubit is the qubit that determines if the $X$-gate would be applied to the target qubit or not. If $q_0$ is in the $|1\rangle$, the state of $q_1$ ...