Photon-Pair Sources and Quantum Cryptography using Continuous Variables


Photon-Pair Sources and Quantum Cryptography using Continuous Variables


Fabian Laudenbach (AIT Austrian Institute of Technology)


The counter-intuitive phenomena of quantum mechanics are currently leaping from their mere exploration to their deployment in real-life applications. Quantum superposition, the uncertainty principle, the no-cloning theorem and, most prominently, quantum entanglement are proven to allow for computing and cryptography algorithms, simulation of complex physical phenomena and sensing of physical quantities in new and beneficial ways which are unparalleled by classical devices. In particular, quantum technologies based on photons offer a straightforward way to protect quantum states from decoherence and, if necessary, transmit them from one place to another reliably. Most applications in the realm of optical quantum technology have successfully been demonstrated in proof-of-principle experiments. However, in order for quantum technologies to unleash their full potential and establish in the shape of wide-spread applications with a true advantage over their classical counterparts, they need to become scalable in size, quantity, performance and cost. This thesis is divided into two parts dealing with different aspects of quantum optics: The first part discusses ways to generate photon pairs with high brightness and, at the same time, high quality in terms of their performance in quantum experiments. The second part provides a theoretical discussion and experimental demonstration of quantum cryptography based on continuous variables — a promising concept to make the striking advantages of quantum communication compatible with off-the-shelf telecom hardware and fibre networks. As I hope, the research presented in both parts of this thesis will, in one way or another, make a contribution to the scalability of quantum technologies and thereby help to enforce the breakthrough of the so-called quantum revolution.