104 research outputs found
Perfect Teleportation and Superdense Coding With W-States
True tripartite entanglement of the state of a system of three qubits can be
classified on the basis of stochastic local operations and classical
communications (SLOCC). Such states can be classified in two categories: GHZ
states and W-states. It is known that GHZ states can be used for teleportation
and superdense coding, but the prototype W-state cannot be. However, we show
that there is a class of W-states that can be used for perfect teleportation
and superdense coding.Comment: 9 pages, no figur
Completely mixed state is a critical point for three-qubit entanglement
Pure three-qubit states have five algebraically independent and one
algebraically dependent polynomial invariants under local unitary
transformations and an arbitrary entanglement measure is a function of these
six invariants. It is shown that if the reduced density operator of a some
qubit is a multiple of the unit operator, than the geometric entanglement
measure of the pure three-qubit state is absolutely independent of the
polynomial invariants and is a constant for such tripartite states. Hence a
one-particle completely mixed state is a critical point for the geometric
measure of entanglement.Comment: two references are added, reshaped, few points are clarifie
On Multiparticle Entanglement via Resonant Interaction between Light and atomic Ensembles
Multiparticle entangled states generated via interaction between narrow-band
light and an ensemble of identical two-level atoms are considered. Depending on
the initial photon statistics, correlation between atoms and photons can give
rise to entangled states of these systems. It is found that the state of any
pair of atoms interacting with weak single-mode squeezed light is inseparable
and robust against decay. Optical schemes for preparing entangled states of
atomic ensembles by projective measurement are described.Comment: 11 pages, 1 figure, revtex
Quantum cobwebs: Universal entangling of quantum states
Entangling an unknown qubit with one type of reference state is generally
impossible. However, entangling an unknown qubit with two types of reference
states is possible. To achieve this, we introduce a new class of states called
zero sum amplitude (ZSA) multipartite, pure entangled states for qubits and
study their salient features. Using shared-ZSA state, local operation and
classical communication we give a protocol for creating multipartite entangled
states of an unknown quantum state with two types of reference states at remote
places. This provides a way of encoding an unknown pure qubit state into a
multiqubit entangled state. We quantify the amount of classical and quantum
resources required to create universal entangled states. This is possibly a
strongest form of quantum bit hiding with multiparties.Comment: Invited talk in II Winter Institute on FQTQO: Quantum Information
Processing, held at S. N. Bose Center for Basic Science, Kolkata, during Jan
2-11, 2002. (To appear in Pramana-J. of Physics, 2002.
Greenberger-Horne-Zeilinger state generation with linear optical elements
We propose a scheme to probabilistically generate Greenberger-Horne-Zeilinger
(GHZ) states encoded on the path degree of freedom of three photons. These
photons are totally independent from each other, having no direct interaction
during the whole evolution of the protocol, which remarkably requires only
linear optical devices to work, and two extra ancillary photons to mediate the
correlation. The efficacy of the method, which has potential application in
distribited quantum computation and multiparty quantum communication, is
analyzed in comparison with similar proposals reported in the recent
literature. We also discuss the main error sources that limit the efficiency of
the protocol in a real experiment and some interesting aspects about the
mediator photons in connection with the concept of spatial nonlocality
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