107,437 research outputs found
Asymmetries in symmetric quantum walks on two-dimensional networks
We study numerically the behavior of continuous-time quantum walks over
networks which are topologically equivalent to square lattices. On short time
scales, when placing the initial excitation at a corner of the network, we
observe a fast, directed transport through the network to the opposite corner.
This transport is not ballistic in nature, but rather produced by quantum
mechanical interference. In the long time limit, certain walks show an
asymmetric limiting probability distribution; this feature depends on the
starting site and, remarkably, on the precise size of the network. The limiting
probability distributions show patterns which are correlated with the initial
condition. This might have consequences for the application of continuous time
quantum walk algorithms.Comment: 9 pages, 12 figures, revtex
Quantum Entanglement Percolation
Quantum communication demands efficient distribution of quantum entanglement
across a network of connected partners. The search for efficient strategies for
the entanglement distribution may be based on percolation theory, which
describes evolution of network connectivity with respect to some network
parameters. In this framework, the probability to establish perfect
entanglement between two remote partners decays exponentially with the distance
between them before the percolation transition point, which unambiguously
defines percolation properties of any classical network or lattice. Here we
introduce quantum networks created with local operations and classical
communication, which exhibit non-classical percolation transition points
leading to the striking communication advantages over those offered by the
corresponding classical networks. We show, in particular, how to establish
perfect entanglement between any two nodes in the simplest possible network --
the 1D chain -- using imperfect entangled pairs of qubits.Comment: 5 pages, 2 figure
Quantum Computing Assisted Medium Access Control for Multiple Client Station Networks
A medium access control protocol based on quantum entanglement has been
introduced by Berces and Imre (2006) and Van Meter (2012). This protocol
entirely avoids collisions. It is assumed that the network consists of one
access point and two client stations. We extend this scheme to a network with
an arbitrary number of client stations. We propose three approaches, namely,
the qubit distribution, transmit first election and temporal ordering
protocols. The qubit distribution protocol leverages the concepts of Bell-EPR
pair or W state triad. It works for networks of up to four CSs. With up to
three CSs, there is no probability of collision. In a four-CS network, there is
a low probability of collision. The transmit first election protocol and
temporal ordering protocols work for a network with any number of CSs. The
transmit first election builds upon the concept of W state of size
corresponding to the number of client stations. It is fair and collision free.
The temporal ordering protocol employs the concepts of Lehmer code and quantum
oracle. It is collision free, has a normalized throughput of 100% and achieves
quasi-fairness.Comment: 18 pages, 12 figures, 3 tables; manuscript under revie
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