A quantum circuit is a combination of logic gates which are connected together by wires. This wire transfer a quantum state from the output of a gate to input of another gate. Then it is connected to a measurement device. The nature of the wire and its practical appearance depends on the technological realization of the qubit. We can visualize trajectories of flying spins as wires. Usually two spins may have their trajectory deflected or enter a zone in which they interact. The case mentioned is that of a two qubit gate.
