Computer networks have been one of the most revolutionary concepts and technologies of the last fifty years. Currently, it is arguably impossible to imagine a world without the internet. And yet, just five decades ago, hardly anybody knew what it even meant. Today, the first quantum computer networks are starting to take shape, along with the promise of a future quantum internet. Quantum networking exploits fundamental primitives of quantum mechanics — most importantly entanglement — to offer a new paradigm of connectivity, which will enhance communication networks and bring some new exciting applications into the scene. Quantum networking has been studied for a few years already. Nevertheless, the current state of the art of quantum networks is somewhat comparable to that of the classical internet at the end of the 1960s: lots of interesting ideas, some experimental demonstrations, and very few reliable testbeds. Scaling up to larger networks of quantum computers requires joint efforts of physics, mathematics, electronics and computer science, at the very least. Bringing these disciplines together is a very bumpy road, given that we do not yet have standard quantum physical platforms to work with, nor universal frameworks and testbeds to validate our hypotheses against. One of the missing links between the highly-complex physical platforms and networks and the high-level descriptions of quantum networking applications is a framework that bridges that gap between these two, providing platform-independent abstractions of the underlying physics to programmers and users of a quantum network. The goal of this thesis is threefold: discuss the requirements for such a framework of abstractions — which we refer to as an operating system — for quantum networks, propose a design for such an operating system, and implement and validate this design on a physical quantum network. Whilst we are interested in measuring the performance of the operating system, we consider our design to be best-effort, and thus we are primarily aiming at establishing a baseline for future research in this field. Nevertheless, we are after a fully-functional product that we hope can be used to push the boundaries of quantum networking demonstrations, and to better understand the challenges of designing and implementing efficient operating systems for quantum network nodes.@en

We introduce NetQASM, a low-level instruction set architecture for quantum internet applications. NetQASM is a universal, platform-independent and extendable instruction set with support for local quantum gates, powerful classical logic and quantum networking operations for remote entanglement generation. Furthermore, NetQASM allows for close integration of classical
logic and communication at the application layer with quantum operations at the physical layer. This enables quantum network applications to be programmed in high-level platform-independent software, which is not possible using any other QASM variants. We implement NetQASM in a series of tools to write, parse, encode and run NetQASM code, which are available online. Our tools include a higher-level software development kit (SDK) in Python, which allows an easy way of programming applications for a quantum internet. Our SDK can be
used at home by making use of our existing quantum simulators, NetSquid and SimulaQron, and will also provide a public interface to hardware released on a future iteration of Quantum Network Explorer.@en

Scaling current quantum communication demonstrations to a large-scale quantum network will require not only advancements in quantum hardware capabilities, but also robust control of such devices to bridge the gap in user demand. Moreover, the abstraction of tasks and services offered by the quantum network should enable platform-independent applications to be executed without the knowledge of the underlying physical implementation. Here we experimentally demonstrate, using remote solid-state quantum network nodes, a link layer, and a physical layer protocol for entanglement-based quantum networks. The link layer abstracts the physical-layer entanglement attempts into a robust, platform-independent entanglement delivery service. The system is used to run full state tomography of the delivered entangled states, as well as preparation of a remote qubit state on a server by its client. Our results mark a clear transition from physics experiments to quantum communication systems, which will enable the development and testing of components of future quantum networks.

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Energy-harvesting devices have enabled Internet of Things applications that were impossible before. One core challenge of batteryless sensors that operate intermittently is reliable timekeeping. State-of-the-art low-power real-time clocks suffer from long start-up times (order of seconds) and have low timekeeping granularity (tens of milliseconds at best), often not matching timing requirements of devices that experience numerous power outages per second. Our key insight is that time can be inferred by measuring alternative physical phenomena, like the discharge of a simple RC circuit, and that timekeeping energy cost and accuracy can be modulated depending on the run-time requirements. We achieve these goals with a multi-tier timekeeping architecture, named Cascaded Hierarchical Remanence Timekeeper (CHRT), featuring an array of different RC circuits to be used for dynamic timekeeping requirements. The CHRT and its accompanying software interface are embedded into a fresh batteryless wireless sensing platform, called Botoks, capable of tracking time across power failures. Low start-up time (max 5 ms), high resolution (up to 1 ms) and run-time reconfigurability are the key features of our timekeeping platform. We developed two time-sensitive batteryless applications to demonstrate the approach: a bicycle analytics tool-where the CHRT is used to track time between revolutions of a bicycle wheel, and wireless communication-where the CHRT enables radio synchronization between two intermittently-powered sensors.

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Energy-neutral Internet of Things requires freeing embedded devices from batteries and powering them from ambient energy. Ambient energy is, however, unpredictable and can only power a device intermittently. Therefore, the paradigm of intermittent execution is to save the program state into non-volatile memory frequently to preserve the execution progress. In task-based intermittent programming, the state is saved at task transition. Tasks are fixed at compile time and agnostic to energy conditions. Thus, the state may be saved either more often than necessary or not often enough for the program to progress and terminate. To address these challenges, we propose Coala, an adaptive and efficient task-based execution model. Coala progresses on a multi-task scale when energy permits and preserves the computation progress on a sub-task scale if necessary. Coala's specialized memory virtualization mechanism ensures that power failures do not leave the program state in non-volatile memory inconsistent. Our evaluation on a real energy-harvesting platform not only shows that Coala reduces runtime by up to 54% as compared to a state-of-the-art system, but also it is able to progress where static systems fail.

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Backscatter has emerged as the dominant paradigm for battery-free networking among the (potentially) trillions of devices in the future Internet of Things, partly because of the order of magnitude smaller energy consumption, but at the cost of collisions, low data rates, and short distances. This position paper explores the alternative approach: using lowpower, yet active radios to communicate among the battery-less swarm. We describe the challenges of using active radios in this context, including lack of tight time guarantees, high listening costs, and intermittent operation. While backscatter is promising, this paper hopes to broaden the conversation around alternative methods for networking the future IoT.@en