Unconditionally Secure Quantum Key Distribution In Higher Dimensions

In search of a quantum key distribution scheme that could stand up for more drastic eavesdropping attack, I discover a prepare-and-measure scheme using N -dimensional quantum particles as information carriers where N is a prime power. Using the Shor-Preskill-type argument, I prove that this scheme is unconditional secure against all attacks allowed by the laws of quantum physics. Incidentally, for N = 2 > 2, each information carrier can be replaced by n entangled qubits. And in this case, I discover an eavesdropping attack on which no unentangled-qubitbased prepare-and-measure quantum key distribution scheme known to date can generate a provably secure key. In contrast, this entangled-qubit-based scheme produces a provably secure key under the same eavesdropping attack whenever N ≥ 16. This demonstrates the advantage of using entangled particles as information carriers to combat certain eavesdropping strategies.