Quantum information processing with photonic graph states
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Quantum information processing is the field of science where the underlying principles of quantum mechanics are explored and exploited to achieve a given goal. In quantum information theory, the so-called graph states can be used as a resource to encode, manipulate and read-out quantum information. In the present thesis, graph states are experimentally realised up to six qubits by means of single photons at telecom wavelength. High-quality graph states and high generation rates are achieved. These photonic graph states are then employed in three independent experiments covering the topics of quantum foundations, quantum key distribution, and quantum metrology respectively. The first experiment shows for the first time the incompatibility of quantum mechanics with the notion of “observer independence”. The second experiment, demonstrates the use of graph states to distribute a secret and common key among several users. A so-called conference key agreement protocol is demonstrated between four users achieving unprecedented rates at which graph state are distributed over long distances. Finally, the third experiment is proposed to demonstrate the feasibility of phase estimation in realistic noisy environments. Graph states’ robustness against noise is enhanced with a novel technique based on experimentally-friendly local encoding. In conclusion, the present thesis provides a comprehensive experimental investigation on the generation and use of graph states for advanced quantum information processing.