Tomographic quantum cryptography with bell diagonal states

Abstract

In the first part of the thesis, a generalized version of the Tomographic Quantum Key Distribution protocol in which the two users Alice and Bob share a Bell diagonal mixed state of two qubits will be presented and its security analyzed. In particular, it will be shown that if an eavesdropper performs a coherent measurement on a number of ancilla states simultaneously, classical methods of secure key distillation are less effective than quantum distillation protocols. Furthermore, certain classes of Bell diagonal states that are resistant to eavesdropping attacks will be identified.In the second part of this thesis, the security of the tomographic protocol using a source which produces entangled photons via an experimental scheme proposed in Phys. Rev. Lett. 92, 37903 (2004) will be analyzed. The range of experimental parameters for which the protocol is secure will be determined.