Characterisation of polarisation-entangled photon source for quantum key distribution.

Abstract

Entanglement in real physical systems has been of great interest due to its importance in quantum mechanics. It has applications related to quantum information science speci cally quantum cryptography since it eliminates the possibility of photon number splitting attack during the key distribution process (Quantum Key Distribution). This thesis deals with creation, detection and characterisation of the correlated polarised photon pairs, which were emitted from a nonlinear BBO crystal via Spontaneous Parametric Down Conversion (SPDC) process. The procedure that leads to the construction of a polarisation-based entangled system is discussed by considering some of the measurement techniques, which can be applied to study fundamental quantum mechanics and its applications in quantum communication. This thesis consists of a set of experiments to validate the entanglement of single photon pairs. The rst experiment realised by generating of polarised based entangled photon pairs. The quantum correlation between the entangled photon pairs have been tested by measuring the visibility of the system and by verifying the maximal violation of CHSH (Clauser, Horne, Shimony and Holt) inequality. In the second experiment, the delity of the system has been measured by carrying out the state tomography to reconstruct the two-photon density matrix and consider the interference e ect of two photons. This helps to study the preservation of the quantum state during the propagation.