In quantum teleportation, a sender (Alice) can send the state of one quantum bit (qubit) to the receiver (Bob). The input to the circuit is the qubit
whose state is to be transported, along with one of a pair of qubits entangled in the Bell basis state (the upper qubit). The other qubit from the Bell pair (the lower qubit) is sent unchanged to Bob. Alice process her two qubits with two quantum gates and measures the output (controlled by the user) yielding two classical bits, which are sent back to Bob. Bob then uses these bits to control the processing on his qubit from the entangled Bell pair through two quantum gates, and this yields a qubit with the same state Alice teleported.