207 research outputs found
Desert navigator: the journey of an ant/ Rüdiger Wehner
No full textIncludes bibliographical references and index"How does a small-brained ant living in the Sahara desert know where it is when searching for prey in the vast expanse of sand and gravel? In Desert Navigator Rudiger Wehner describes and illustrates, in a lively and lucid narrative, how the ants accomplish their navigational tasks by using visual cues in the sky that humans are unable to see, the Earth's magnetic field, the direction of the wind, a step counter, an optic-flow meter and path integrator as well panoramic 'snapshots' of their landmark surroundings, and how they combine all this information to optimally steer their courses. Moreover, a glimpse into the navigator's brain reveals the kind of neural circuitry mediating the observed behavior. Truly, the desert ants have now become model organisms in the study of animal navigation. In telling this discovery story, which he enriches by frequent excursions to other animals and even humans, the author lets us participate in the joys and challenges experienced on a fascinating journey to the desert navigator"--Setting the scene -- The thermophiles -- Finding directions -- Estimating distances -- Integrating paths -- Using landmarks -- Organizing the journey1 online resource (392 pages
Quantum resource-saving protocols for early quantum networks
No full textThe Internet as we know it has had an immense impact on the way we communicate. We can now do it faster and more securely than ever before. Enabling quantum communication between any two points on Earth is the next step towards even more secure communication. This is the goal of the quantum internet. Although it is hard to predict all of the applications for the quantum internet, many protocols running on a network connecting nodes able to process qubits have already been identified. Typically, these applications require many qubits to be realized, a requirement which will not likely be met in the early quantum internet.QID/Wehner Grou
SimulaQron—a simulator for developing quantum internet software
No full textWe introduce a simulator of a quantum internet with the specific goal to support software development. A quantum internet consists of local quantum processors, which are interconnected by quantum communication channels that enable the transmission of qubits between the different processors. While many simulators exist for local quantum processors, there is presently no simulator for a quantum internet tailored towards software development. Quantum internet protocols require both classical as well as quantum information to be exchanged between the network nodes, next to the execution of gates and measurements on a local quantum processor. This requires quantum internet software to integrate classical communication programming practises with novel quantum ones. SimulaQron is built to enable application development and explore software engineering practises for a quantum internet. SimulaQron can be run on one or more classical computers to simulate local quantum processors, which are transparently connected in the background to enable the transmission of qubits or the generation of entanglement between remote processors. Application software can access the simulated local quantum processors to execute local quantum instructions and measurements, but also to transmit qubits to remote nodes in the network. SimulaQron features a modular design that performs a distributed simulation based on any existing simulation of a quantum computer capable of integrating with Python. Programming libraries for Python and C are provided to facilitate application development.Accepted Author ManuscriptQID/Wehner GroupQuantum Internet DivisionQuantum Information and Softwar
Multiplexed entanglement generation over quantum networks using multi-qubit nodes
No full textQuantum networks distributed over distances greater than a few kilometres will be limited by the time required for information to propagate between nodes. We analyse protocols that are able to circumvent this bottleneck by employing multi-qubit nodes and multiplexing. For each protocol, we investigate the key network parameters that determine its performance. We model achievable entangling rates based on the anticipated near-term performance of nitrogen-vacancy centres and other promising network platforms. This analysis allows us to compare the potential of the proposed multiplexed protocols in different regimes. Moreover, by identifying the gains that may be achieved byimproving particular network parameters, our analysis suggests the most promising avenues for research and development of prototype quantum networks.Accepted Author ManuscriptQID/Hanson LabQID/Wehner GroupQuantum Internet DivisionQuantum Information and SoftwareQN/Hanson La
Hybrid Quantum Networks for High-Fidelity Entanglement Distribution
No full textWe present an architecture for multiplexed quantum repeaters using local connectivity to improve fidelity in entanglement distribution. Simulations indicate our scheme achieves rates comparable to competing schemes, with fidelity improvements that increase with repeater size.Virtual/online event due to COVID-19QID/Wehner GroupQuantum Internet DivisionQuantum Information and Softwar
High-fidelity Greenberger-Horne-Zeilinger state generation within nearby nodes
No full textGenerating entanglement in a distributed scenario is a fundamental task for implementing the quantum network of the future. We here report a protocol that uses only linear optics for generating Greenberger-Horne-Zeilinger states with high fidelities in a nearby node configuration. Moreover, we analytically show that the scheme is optimal for certain initial states in providing the highest success probability for sequential protocols. Finally, we give some estimates for the generation rate in a real scenario.QID/Wehner GroupQuantum Internet DivisionQuantum Information and Softwar
Distributing entanglement in quantum networks
No full textThe research presented in this thesis focused on the problem of entanglement distribution. Simply put, the two main problems facing (practical) implementation of entanglement distribution over quantum networks are loss and noise. Quantum repeaters are meant to overcome the effects of loss, but in practice their implementation always comes at the cost of more incurred noise. This additional noise can be overcome by the use of entanglement distillation.In the first two chapters, we focused on the assessment of a basic building block for quantum networks, a single quantum repeater. We then considered finding schemes for the concatenation of multiple such quantum repeaters, along with the inclusion of basic distillation protocols. Finally, we considered a systematic way of optimising over a relevant class of (more complex) distillation protocols.QID/Wehner Grou
Quantum Network Utility Maximization
No full textNetwork Utility Maximization (NUM) is a mathe-matical framework that has endowed researchers with powerful methods for designing and analyzing classical communication protocols. NUM has also enabled the development of distributed algorithms for solving the resource allocation problem, while at the same time providing certain guarantees, e.g., that of fair treatment, to the users of a network. We extend here the notion of NUM to quantum networks, and propose three quantum utility functions - each incorporating a different entanglement measure. We aim both to gain an understanding of some of the ways in which quantum users may perceive utility, as well as to explore structured and theoretically-motivated methods of simultaneously servicing multiple users in distributed quantum systems. Using our quantum NUM constructions, we develop an optimization framework for networks that use the single-photon scheme for entanglement generation, which enables us to solve the resource allocation problem while exploring rate-fidelity tradeoffs within the network topologies that we consider. We learn that two of our utility functions, which are based on distillable entanglement and secret key fraction, are in close agreement with each other and produce similar solutions to the optimization problems we study. While these two utilities place a higher emphasis on end-to-end fidelity, our third utility- based on entanglement negativity - has more favorable mathematical properties, and tends to place a higher value on the rate at which users receive entangled resources. These contrasting behaviors thus provide ideas regarding the suitability of quantum network utility definitions to different quantum applications.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Quantum Computer ScienceCommunication QuTechQID/Wehner Grou
Reply to "comment on 'Fully device-independent conference key agreement'"
No full textIn this Reply we correct a mistake that we made in the correctness proofs of our protocol. Specifically, the Bell inequality we used ensures security but does not allow us to produce a key. In this Reply we explain and correct this mistake by adjusting the Bell inequality we used in the proof. Incidentally, this correction leads to slightly better asymptotic key rates. Importantly, none of the conclusions of the article are affected.QID/Wehner GroupQuantum Internet DivisionQuantum Information and Softwar
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