Experimental Optical Quantum Science: Efficient Multi-Photon Sources for Quantum Information Science

Abstract

Quantum optics promises excellent capabilities for experimental demonstrations of quantum information processing. So far, the practical implementation of protocols displaying a clear quantum advantage has been limited, as they rely on perfect quantum states and high delity measurements. Additionally, the fragile nature of the quantum states makes them susceptible to imperfections in measurement devices, and environmental loss. Two of the key challenges for quantum technologies are that of producing single photons, and pairs of entangled photons, more eciently, and overcoming the detrimental effects of photon loss. The research presented in this thesis tackles the practical realisation of quantum-enhanced protocols by improving spontaneous parametric down conversion for producing photon pairs. I present a spontaneous parametric down-conversion source of frequency-uncorrelated polarisation-entangled photon pairs at telecom wavelengths. The source provides photon pairs that display-simultaneously-the key properties for high-performance quantum information tasks and the investigation of fundamental quantum physics. Specifically, the source provides high heralding efficiency, high quantum state purity and high entangled-state fidelity at the same time. Among the different tests applied, perfect non-classical interference between photons from independent sources with a visibility of (1005)% was observed. Additionally, the polarisation-unentangled version of the source achieved symmetric heralding efficiencies of up to (82 2)%. The following two experiments presented in this thesis make use of these high-performance sources to implement an entanglement verication protocol over a high-loss quantum channel, and to perform a quantum metrology experiment, both of which were not previously achievable with existing sources or designs.