Free-space quantum cryptography systems for next generation communication networks

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Security is an endless game of cat and mouse. Throughout the history, people have built the castle walls higherand thicker, yet this has not prevented the marauders find a clever way inside. The history of cryptographynarrates stories of many so-called unbreakable codes that have been cracked. This is due to the fact thatconventional cryptosystems offer only computational security based on some mathematical complexity of theencryption. A breakthrough in quantum computing, for example, would leave today's cryptosystems totallyvulnerable to threats. Based on the firm laws of physics rather than unproven foundations of mathematicalcomplexity, quantum cryptography provides a radically different solution for encryption and promisesunconditional security. Quantum cryptography systems are typically built between two nodes connected to eachother through fibre optic. This proposal focuses on quantum cryptography systems operating over free-spaceoptical channels as a cost-effective and license-free alternative to fibre optic counterparts. From acommunication theory perspective, we address the performance analysis and optimization of free-spacequantum cryptography systems investigating the achievable rates and devising methods to approach them underpractical constraints.