We are currently experiencing a rapid development of quantum information, a new branch of science, being an interdisciplinary of quantum physics, information theory, telecommunications, computer science, and many others. This new science branch was born in the middle of the eighties, developed rapidly during the nineties, and in the current decade has brought a technological breakthrough in creating secure quantum key distribution (QKD), quantum secret sharing, and exciting promises in diverse technological fields. Recent QKD experiments have achieved high rate QKD at 200 km distance in optical fiber. Significant QKD results have also been achieved in free-space. Due to the rapid broadband access deployment in many industrialized countries and the standing increasing transmission security treats, the natural development awaiting quantum communications, being a part of quantum information, is its migration into commercial switched telecom networks. Such a migration concerns both multiuser quantum key distribution and multiparty quantum secret sharing that have been the main goal of my PhD studies. They are also the main concern of the thesis. Our research efforts in multiuser QKD has led to a development of the five-user setup for transmissions over switched fiber networks in a star and in a tree configuration. We have achieved longer secure quantum information distances and implemented more nodes than other multi-user QKD experiments. The measurements have shown feasibility of multiuser QKD over switched fiber networks, using standard fiber telecom components. Since circular architecture networks are important parts of both intranets and the Internet, Sagnac QKD has also been a subject of our research efforts. The published experiments in this area have been very few and results were not encouraging, mainly due to the single mode fiber (SMF) birefringence. Our research has led to a development of a computer controlled birefringence compensation in Sagnac that open the door to both classical and quantum Sagnac applications. On the quantum secret sharing side, we have achieved the first quantum secret sharing experiment over telecom fiber in a five-party implementation using the "plug & play" setup and in a four-party implementation using Sagnac configuration. The setup measurements have shown feasibility and scalability of multiparty quantum communication over commercial telecom fiber networks.

[pt] Os protocolos de comunicação quântica são essenciais para a transmissão segura de informações, utilizando os princípios da mecânica quântica para alcançar uma segurança inatingível por sistemas criptográficos clássicos. Diferentemente dos métodos tradicionais que dependem de chaves criptográficas convencionais, os protocolos quânticos exploram propriedades únicas dos sistemas quânticos para garantir a segurança da comunicação. No entanto, a implementação prática da distribuição quântica de chaves (QKD) é desafiada por erros introduzidos durante a geração e transmissão de estados quânticos e pela possível presença de espiões. Esta dissertação explora algumas das estratégias mais usadas para estimativa de erros, correção de erros e amplificação de privacidade em sistemas de QKD. Por meio de uma revisão bibliográfica e simulações abrangentes, o estudo avalia as técnicas mais eficazes em cada área. O objetivo final desta análise é desenvolver um método a ser implementado na Rede Rio Quântica, uma rede de comunicação quântica metropolitana que interliga as instituições PUC-Rio, CBPF e UFRJ por meio de fibras ópticas e a UFF através de um canal de espaço livre. Os resultados destacam a importância de otimizar as medidas de correção de erros e privacidade para melhorar a confiabilidade e a segurança das redes de comunicação quântica. / [en] Quantum communication protocols are essential for secure transmission of information, utilizing the principles of quantum mechanics to achieve security unattainable by classical cryptographic systems. Unlike traditional methods that rely on conventional cryptographic keys, quantum protocols exploit unique properties of quantum systems to ensure communication security. However, the practical implementation of quantum key distribution (QKD) is challenged by errors introduced during the generation and transmission of quantum states and the potential presence of eavesdroppers. This thesis explores some of the most commonly used strategies for error estimation, error reconciliation, and privacy amplification within QKD systems. Through a literature review and comprehensive simulations, the study evaluates the most effective techniques in each area. The ultimate goal of this analysis is to develop a method to be implemented on Rede Rio Quântica, a metropolitan quantum communication network interlinking the institutions PUC-Rio, CBPF and UFRJ via optical fibers and UFF through a free-space channel. The findings underscore the importance of optimizing error correction and privacy measures to enhance the reliability and security of quantum communication networks.