Entanglement-enhanced quantum key distribution
Olli Ahonen, Mikko Möttönen, Jeremy L. O’Brien · Physical Review A · 2008
We present and analyze a quantum key distribution protocol based on sending entangled $N$-qubit states instead of single-qubit ones as in the trail-blazing scheme by Bennett and Brassard 1984 (BB84). Since the qubits are sent and acknowledged individually, an eavesdropper is limited to accessing them one by one. In an intercept-resend attack, this fundamental restriction allows one to make the eavesdropper's information on the transmitted key vanish if even one of the qubits is not intercepted. The implied upper bound $1∕(2N)$ for this information is further shown not to be the lowest, as the information can be reduced to less than 30% of that in the BB84 scheme in the case $N=2$. In general, the protocol is at least as secure as BB84.