The principles of quantum teleportation. The sender A and the receiver B share the entangled pair of qubits as a quantum channel provided by entanglement equipment from path 1 and path 2. Sender A performs a joint Bell-state measurement on the initial particle and projects them onto an entangled state, and then send the result of the measurement to receiver B by classical path. Finally receiver B performs a unitary transformation to the particle in the initial state.