Topology Adaption for the Quantum Internet

In the quantum repeater networks of the quantum Internet, the varying stability of entangled quantum links makes dynamic topology adaption an emerging issue. Here we define an efficient topology adaption method for quantum repeater networks. The model assumes the random failures of entangled links and several parallel demands from legal users. The shortest path defines a set of entangled links for which the probability of stability is above a critical threshold. The scheme is utilized in a base-graph of the overlay quantum network to provide an efficient shortest path selection for the demands of all users of the network. We study the problem of entanglement assignment in a quantum repeater network, prove its computational complexity, and show an optimization procedure. The results are particularly convenient for future quantum networking, quantum-Internet, and experimental long-distance quantum communications.Comment: 17 pages, Journal-ref: Quant. Inf. Proc. (2018

Towards a Distributed Quantum Computing Ecosystem

The Quantum Internet, by enabling quantum communications among remote quantum nodes, is a network capable of supporting functionalities with no direct counterpart in the classical world. Indeed, with the network and communications functionalities provided by the Quantum Internet, remote quantum devices can communicate and cooperate for solving challenging computational tasks by adopting a distributed computing approach. The aim of this paper is to provide the reader with an overview about the main challenges and open problems arising with the design of a Distributed Quantum Computing ecosystem. For this, we provide a survey, following a bottom-up approach, from a communications engineering perspective. We start by introducing the Quantum Internet as the fundamental underlying infrastructure of the Distributed Quantum Computing ecosystem. Then we go further, by elaborating on a high-level system abstraction of the Distributed Quantum Computing ecosystem. Such an abstraction is described through a set of logical layers. Thereby, we clarify dependencies among the aforementioned layers and, at the same time, a road-map emerges

Semi-Quantum Conference Key Agreement (SQCKA)

A need in the development of secure quantum communications is the scalable extension of key distribution protocols. The greatest advantage of these protocols is the fact that its security does not rely on mathematical assumptions and can achieve perfect secrecy. In order to make these protocols scalable, has been developed the concept of Conference Key Agreements, among multiple users. In this thesis we propose a key distribution protocol among several users using a semi-quantum approach. We assume that only one of the users is equipped with quantum devices and generates quantum states, while the other users are classical, i.e., they are only equipped with a device capable of measuring or reflecting the information. This approach has the advantage of simplicity and reduced costs. We prove our proposal is secure and we present some numerical results on the lower bounds for the key rate. The security proof applies new techniques derived from some already well established work. From the practical point of view, we developed a toolkit called Qis|krypt⟩ that is able to simulate not only our protocol but also some well-known quantum key distribution protocols. The source-code is available on the following link: - https://github.com/qiskrypt/qiskrypt/.Uma das necessidades no desenvolvimento de comunicações quânticas seguras é a extensão escalável de protocolos de distribuição de chaves. A grande vantagem destes protocolos é o facto da sua segurança não depender de suposições matemáticas e poder atingir segurança perfeita. Para tornar estes protocolos escaláveis, desenvolveu-se o conceito de Acordo de Chaves de Conferência, entre múltiplos utilizadores. Nesta tese propomos um protocolo para distribuição de chaves entre vários utilizadores usando uma abordagem semi-quântica. Assumimos que apenas um dos utilizadores está equipado com dispositivos quânticos e é capaz de gerar estados quânticos, enquanto que os outros utilizadores são clássicos, isto é, estão apenas equipados com dispositivos capazes de efectuar uma medição ou refletir a informação. Esta abordagem tem a vantagem de ser mais simples e de reduzir custos. Provamos que a nossa proposta é segura e apresentamos alguns resultados numéricos sobre limites inferiores para o rácio de geração de chaves. A prova de segurança aplica novas técnicas derivadas de alguns resultados já bem estabelecidos. Do ponto de vista prático, desenvolvemos uma ferramenta chamada Qis|krypt⟩ que é capaz de simular não só o nosso protocolo como também outros protocolos distribuição de chaves bem conhecidos. O código fonte encontra-se disponível no seguinte link: - https://github.com/qiskrypt/qiskrypt/