Figure 1

QKD using entanglement swapping. The bold line means qubits are entangled and the dotted line implies a Bell measurement is performed on the qubits. (i) Alice and Bob each prepare arbitrary states, either in Bell or on rotated bases, known only to themselves. (ii) Each sends one qubit of the states to the other party. (iii) After they confirm publicly the other person received the qubit and announce the choice of basis for initial preparation, Alice and Bob perform Bell measurements on 1 and 4, and 2 and 3, respectively. (iv) Alice and Bob now announce which Bell states had been prepared (or their measurement result for scheme II), and they are able to find out the correlated measurement results (or initial state preparation for scheme II).Reuse & Permissions

Figure 2

Eavesdropping scheme on the proposed entanglement swapping QKD. As in Fig. 1, the bold line means the qubits are entangled and the dotted line implies a Bell measurement is performed on the qubits. (i) While Alice and Bob prepare arbitrary states, Eve also prepares ${\Phi }_{56}^{+}$. (ii) Eve intercepts qubit 2 sent by Alice and sends qubit 6 to Bob instead. (iii) Eve performs a Bell measurement on qubits 5 and 4. (iv) Eve then performs a local operation on qubit 2 and sends it back to Alice.Reuse & Permissions