Quantum correlations arising from measurements on pairs of entangled particles are often referred to as the most non-classical feature of quantum mechanics. As such, they have found a role in many fundamental tests of quantum mechanics and most emerging applications in the field of quantum communication. The most well-known fundamental test is the Bell inequality. Its repeated violation in countless experiments has convinced physicists that local hidden variables cannot describe the correlations arising from measurements on entangled particles. On the application side, quantum correlations have been used in quantum key distribution, which aims to provably secure messages during transmission, and quantum repeaters, which are essential for future long-distance quantum communication.
The main goal of this thesis was to use quantum entanglement for new fundamental studies and quantum communication applications. Towards this end, we developed a high-fidelity source of entanglement and used it in a fundamental test where we bounded the predictive power any physical theory could have about the outcomes of measurements on entangled particles. Secondly, we made use of entangling measurements to develop a new quantum cryptography system based on the promising MDI-QKD protocol, which protects users from otherwise undetectable hacking attacks. We developed a detailed model of MDI-QKD systems with which one can optimize any implementation, deployed our MDI-QKD system across the city of Calgary, and demonstrated the feasibility of this protocol and of long-distance entangling measurements. Thirdly, we have built a source of entanglement compatible with quantum memories, which is an essential ingredient of quantum repeaters. We then demonstrated several crucial steps towards a functioning quantum repeater, including the preservation of entanglement during storage and, more generally, the entire photonic wavefunction. While further work is required to bring our demonstrations to real-world applications, we are confident that they will prove useful in guiding future developments.