Quantum networks: design, simulation and applications

Coupling quantum devices opens new possibilities, and allows one to unlock their full potential. Such quantum networks exist at different scales, and we describe methods to realize and operate them. We show how multipartite entangled states can serve as a valuable resource to fulfill network requests on demand. Such entanglement-based or entanglement assisted quantum networks offer new features such as speeding up network requests, and network optimization independent of the underlying physical structure. We show how to simulate, design and optimize such entanglement-based networks, and study their performance under noise. To this aim, we introduce efficient classical simulation methods that we utilize to study networks with thousands of nodes. We also demonstrate how present-day quantum computers can be utilized to simulate and optimize large-scale quantum networks. We show how noise and imperfections of the quantum computer can be used as an asset rather than a hindrance, by transforming the inherent noise of the quantum computer to the desired target noise of network components and processes

In a second part, we consider quantum sensor networks and discuss how logical encodings can be used to obtain selective and noise resilient sensing of spatially correlated signals, including waves. We demonstrate how a generalization of the approach can be used to control interactions between remote systems with always-on, distance dependent long-ranged couplings, solely by single qubit local control. We utilize this approach to demonstrate the generation of remote entanglement, of a universal quantum simulator based on logical system, and a method to mitigate the effect of thermal fluctuations.