1,720,967 research outputs found
Testing Bell's inequality using ballistic electrons in semiconductors
Get PDFWe propose an experiment to test Bell's inequality violation in condensed-matter physics. We show how to generate, manipulate, and detect entangled states using ballistic electrons in Coulomb-coupled semiconductor quantum wires. Due to its simplicity (only five gates are required to prepare entangled states and to test Bell's inequality), the proposed semiconductor-based scheme can be implemented with currently available technology. Moreover, its basic ingredients may play a role towards large-scale quantum-information processing in solid-state devices
Bipartite entanglement and entropic boundary law in lattice spin systems
Get PDFWe investigate bipartite entanglement in spin-1/2 systems on a generic lattice. For states that are an equal superposition of elements of a group G of spin flips acting on the fully polarized state parallel to0>(xn), we find that the von Neumann entropy depends only on the boundary between the two subsystems A and B. These states are stabilized by the group G. A physical realization of such states is given by the ground state manifold of the Kitaev's model on a Riemann surface of genus g. For a square lattice, we find that the entropy of entanglement is bounded from above and below by functions linear in the perimeter of the subsystem A and is equal to the perimeter (up to an additive constant) when A is convex. The entropy of entanglement is shown to be related to the topological order of this model. Finally, we find that some of the ground states are absolutely entangled, i.e., no partition has zero entanglement. We also provide several examples for the square lattice
Ground state entanglement and geometric entropy in the Kitaev model
Get PDFWe study the entanglement properties of the ground state in Kitaev's model. This is a two-dimensional spin system with a torus topology and non-trivial four-body interactions between its spins. For a generic partition (A, B) of the lattice we calculate analytically the von Neumann entropy of the reduced density matrix p(A) in the ground state. We prove that the geometric entropy associated with a region A is linear in the length of its boundary. Moreover, we argue that entanglement can probe the topology of the system and reveal topological order. Finally, no partition has zero entanglement and we find the partition that maximizes the entanglement in the given ground state. (c) 2005 Elsevier B.V. All rights reserved
Quantum entanglement in states generated by bilocal group algebras
Get PDFGiven a finite group G with a bilocal representation, we investigate the bipartite entanglement in the state constructed from the group algebra of G acting on a separable reference state. We find an upper bound for the von Neumann entropy for a bipartition (A,B) of a quantum system and conditions to saturate it. We show that these states can be interpreted as ground states of generic Hamiltonians or as the physical states in a quantum gauge theory and that under specific conditions their geometric entropy satisfies the entropic area law. If G is a group of spin flips acting on a set of qubits, these states are locally equivalent to 2-colorable (i.e., bipartite) graph states and they include Greenberger-Horne-Zeilinger, cluster states, etc. Examples include an application to qudits and a calculation of the n-tangle for 2-colorable graph states
Ultrafast Quantum Information Processing in Nanostructured Semiconductors
No full textWe shall review two implementation proposals for quantum information processing based on charge degrees of freedom in semiconductor nanostructures. An all-optical implementation scheme using semiconductor macroatoms/molecules will be discussed. The computational degrees of freedom in this proposal are interband optical transitions driven by ultrafast sequences of multicolor laser-pulse trains. The conditional dynamics necessary for universal quantum computation is provided by exciton-exciton coupling between different quantum dots in an array. We shall also discuss an alternative scheme based on transport of ballistic electrons in coupled semiconductor quantum wires. In the framework of such implementation strategy, we shall finally discuss a potential simple way for testing violation of Bell's inequality in a condensed-matter setting
Simulation of entangled electronic states in semiconductor quantum wires
No full textA system able to produce entangled two-electron states is proposed and studied by means of numerical simulations. The basic device consists of a couple of semiconductor quantum wires in which single electrons are injected and propagated coherently. Coulomb coupling between two electrons in two different wires arises in a region where the wires get close to each other. The strength of this interaction can be tuned with a proper design of the system geometry. It is shown that it is possible to create the four entangled Bell states for the two-particle wave function
Simulation of entangled electronic states in semiconductor quantum wires
No full textA system able to produce entangled two-electron states is proposed and studied by means of numerical simulations. The basic device consists of a couple of semiconductor quantum wires in which single electrons are injected and propagated coherently. Coulomb coupling between two electrons in two different wires arises in a region where the wires get close to each other. The strength of this interaction can be tuned with a proper design of the system geometry. It is shown that it is possible to create the four entangled Bell states for the two-particle wave function. (C) 2002 Elsevier Science B.V. All rights reserved
Quantum information processing using semiconductor nanostructures
No full textWe shall review two implementation proposals for quantum information processing based on charge degrees-of-freedom in semiconductor nanostructures. An all-optical implementation scheme using semiconductor macroatoms/molecules will be discussed. The computational degrees-of-freedom in this proposal are interband optical transitions driven by ultrafast sequences of multicolor laser-pulse trains. The conditional dynamics necessary for universal quantum computation is provided by exciton-exciton coupling between different quantum dots in an array. We shall also discuss an alternative scheme based on transport of ballistic electrons in coupled semiconductor quantum wires. In the framework of such implementation strategy, we shall finally discuss a potential simple way for testing violation of Bell's inequality in a condensed-matter setting
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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