6,490 research outputs found
Universal quantum computation by discontinuous quantum walk
Quantum walks are the quantum-mechanical analog of random walks, in which a
quantum `walker' evolves between initial and final states by traversing the
edges of a graph, either in discrete steps from node to node or via continuous
evolution under the Hamiltonian furnished by the adjacency matrix of the graph.
We present a hybrid scheme for universal quantum computation in which a quantum
walker takes discrete steps of continuous evolution. This `discontinuous'
quantum walk employs perfect quantum state transfer between two nodes of
specific subgraphs chosen to implement a universal gate set, thereby ensuring
unitary evolution without requiring the introduction of an ancillary coin
space. The run time is linear in the number of simulated qubits and gates. The
scheme allows multiple runs of the algorithm to be executed almost
simultaneously by starting walkers one timestep apart.Comment: 7 pages, revte
Preserving Context Privacy in Distributed Hash Table Wireless Sensor Networks.
Wireless Sensor Networks (WSN) are often deployed in hostile or difficult scenarios, such as military battlefields and disaster recovery, where it is crucial for the network to be highly fault tolerant, scalable and decentralized. For this reason, peer-to-peer primitives such as Distributed Hash Table (DHT), which can greatly enhance the scalability and resilience of a network, are increasingly being introduced in the design of WSN's. Securing the communication within the WSN is also imperative in hostile settings. In particular, context information, such as the network topology and the location and identity of base stations (which collect data gathered by the sensors and are a central point of failure) can be protected using traffic encryption and anonymous routing. In this paper, we propose a protocol achieving a modified version of onion routing over wireless sensor networks based on the DHT paradigm. The protocol prevents adversaries from learning the network topology using traffic analysis, and therefore preserves the context privacy of the network. Furthermore, the proposed scheme is designed to minimize the computational burden and power usage of the nodes, through a novel partitioning scheme and route selection algorithm
A Survey on Routing in Anonymous Communication Protocols
The Internet has undergone dramatic changes in the past 15 years, and now forms a global communication platform that billions of users rely on for their daily activities. While this transformation has brought tremendous benefits to society, it has also created new threats to online privacy, ranging from profiling of users for monetizing personal information to nearly omnipotent governmental surveillance. As a result, public interest in systems for anonymous communication has drastically increased. Several such systems have been proposed in the literature, each of which offers anonymity guarantees in different scenarios and under different assumptions, reflecting the plurality of approaches for how messages can be anonymously routed to their destination. Understanding this space of competing approaches with their different guarantees and assumptions is vital for users to understand the consequences of different design options. In this work, we survey previous research on designing, developing, and deploying systems for anonymous communication. To this end, we provide a taxonomy for clustering all prevalently considered approaches (including Mixnets, DC-nets, onion routing, and DHT-based protocols) with respect to their unique routing characteristics, deployability, and performance. This, in particular, encompasses the topological structure of the underlying network; the routing information that has to be made available to the initiator of the conversation; the underlying communication model; and performance-related indicators such as latency and communication layer. Our taxonomy and comparative assessment provide important insights about the differences between the existing classes of anonymous communication protocols, and it also helps to clarify the relationship between the routing characteristics of these protocols, and their performance and scalability
On the experimental verification of quantum complexity in linear optics
The first quantum technologies to solve computational problems that are
beyond the capabilities of classical computers are likely to be devices that
exploit characteristics inherent to a particular physical system, to tackle a
bespoke problem suited to those characteristics. Evidence implies that the
detection of ensembles of photons, which have propagated through a linear
optical circuit, is equivalent to sampling from a probability distribution that
is intractable to classical simulation. However, it is probable that the
complexity of this type of sampling problem means that its solution is
classically unverifiable within a feasible number of trials, and the task of
establishing correct operation becomes one of gathering sufficiently convincing
circumstantial evidence. Here, we develop scalable methods to experimentally
establish correct operation for this class of sampling algorithm, which we
implement with two different types of optical circuits for 3, 4, and 5 photons,
on Hilbert spaces of up to 50,000 dimensions. With only a small number of
trials, we establish a confidence >99% that we are not sampling from a uniform
distribution or a classical distribution, and we demonstrate a unitary specific
witness that functions robustly for small amounts of data. Like the algorithmic
operations they endorse, our methods exploit the characteristics native to the
quantum system in question. Here we observe and make an application of a
"bosonic clouding" phenomenon, interesting in its own right, where photons are
found in local groups of modes superposed across two locations. Our broad
approach is likely to be practical for all architectures for quantum
technologies where formal verification methods for quantum algorithms are
either intractable or unknown.Comment: Comments welcom
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