Cloning of High-Dimensional Quantum States

Abstract

In Chap. 2, I describe a simple intercept-and-resend attack that an eavesdropper can perform on a QKD link. I explain how Alice encoding information in two or more randomly chosen mutually unbiased bases compels Eve to measure the quantum states in incorrect basis, resulting in increased quantum bit error rate in the raw key. In principle, Eve could circumvent detection if she was in possession of a quantum device that could copy an information-carrying photon on a different photon. Such a device would allow her to copy all the quantum states in the channel, one at a time, and then measure the quantum states after Alice and Bob discuss their basis choice. However, as discussed in Chap. 1, there is a fundamental limiting principle, known as the no-cloning theorem, that forbids Eve from cloning unknown quantum states in the quantum channel.