Quantum Measurement and Cloning of States

Abstract

In this thesis aspects of quantum measurement and cloning of states are explored. Quantum cloning has been a subject of interest for a long time, starting with the no-cloning theorem. The no-cloning theorem states that it is impossible to create an identical copy of an arbitrary quantum state. While perfect copying is not possible, one can consider imperfect copying. In such a scenario, one can copy all quantum states at the same level of imperfection and achieve optimal quantum cloning. Optimal cloning can be realised using atom-photon interactions, where one tries to copy photon polarisation states. Even this corresponds to a highly idealised situation, free from sources of noise that are generally present in a laboratory. Our aim is to study atom-photon interactions with the introduction of thermal noise in the atomic system, the photonic system and both, thereby studying to what extent the thermal noise corrupts the cloning process by comparing the initial and final states using the concept of fidelity.