multi-partite entanglement ; secure communication; quantum communication
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Quantum communication has traditionally focused on point-to-point quantum key dis- tribution and applications that can build on these one-dimensional (1D) networks. Progress in quantum technologies and their capabilities have also started to consider what else can be achieved beyond this relatively simple paradigm. This ranges from quantum sensor net- works to what is sometimes called the quantum internet, where a wide variety of quantum technologies, including distributed quantum computers, may be exploited, or connected by quantum repeaters or satellites. There are also novel ideas such as broadcast protocols or for secret sharing, for secure quantum communication beyond the 1D regime, as well as novel all-photonic quantum repeater schemes. These are typically built on entanglement-based approaches. Many of these have also been identified as part of the long-term vision for the recently announced European Quantum Technologies Flagship. Nonetheless, many funda- mental questions remain to be addresses and many of the technologies still require significant progress, before these can be realised.Our previous SNSF project focused on developing advanced photonic and entanglement based technologies for the generation, distribution, measurement and certification of quantum systems for quantum communication in a so-called “device-independent” fashion. In partic- ular, in bridging the gap between abstract security proofs and the security of real world systems and to lay the foundations for improved security for practical quantum communica- tion applications. This, however, was primarily done for quantum random number generation or simple point-to-point scenarios. In the case of the more practical weak-pulsed schemes this made significant advances, which have led to a patent and a SNSF Bridge project to explore and implement the innovation potential. While fully DI protocols remain extremely challenging, many lessons in terms of the trade-off between assumptions and practicality were learnt that will be of relevance for the more complex systems to be studied here.It is our aim here to build on our recent work and develop the experimental and theoret- ical tools needed to generate, distribute, measure and certify these more complex quantum photonic networks. There are two main directions. The first to build on our previous work on 1D multi-photon networks with integrated photonic sources and to study device inde- pendent concepts related to bi-locality and the distribution of entanglement in a quantum repeater architecture. The second research direction uses our path-entangled approach to explore, both experimentally and theoretically, multi-partite 2D networks targeting certifica- tion experiments of 10-100 genuinely entangled qubits. We will also concurrently continue to push the development of the underlying quantum technologies like sources and detectors and quantum frequency converters, increasingly exploiting integrated photonic solutions. One of the goals here is to develop the building blocks for the next generation of multi-photon experiments and there compatibility with quantum dots and quantum memories.These all represent serious challenges in terms of the certification and distribution of entanglement in quantum networks due to the scaling of the number of measurements and the performance requirements of the underlying technologies. As always, we will be constantly assessing the progress, both of the project and across the field, to ensure we successfully achieve our main objectives.