Unconditionally Secure Key Distribution In Higher Dimensions By Depolarization

Abstract

This paper presents a prepare-and-measure scheme using $N$-dimensional quantum particles as information carriers where $N$ is a prime power. One of the key ingredients used to resist eavesdropping in this scheme is to depolarize all Pauli errors introduced to the quantum information carriers. Using the Shor-Preskill-type argument, we prove that this scheme is unconditionally secure against all attacks allowed by the laws of quantum physics. For $N=2^n>2$, each information carrier can be replaced by $n$ entangled qubits. In this case, there is a family of eavesdropping attacks on which no unentangled-qubit-based prepare-and-measure quantum key distribution scheme known to date can generate a provably secure key. In contrast, under the same family of attacks, our entangled-qubit-based scheme remains secure whenever $2^n\ge 4$. This demonstrates the advantage of using entangled particles as information carriers and of using depolarization of Pauli errors to combat eavesdro