90 research outputs found
Teleportation of a qubit using entangled non-orthogonal states: A comparative study
The effect of non-orthogonality of an entangled non-orthogonal state based
quantum channel is investigated in detail in the context of the teleportation
of a qubit. Specifically, average fidelity, minimum fidelity and minimum
assured fidelity (MASFI) are obtained for teleportation of a single qubit state
using all the Bell type entangled non-orthogonal states known as quasi Bell
states. Using Horodecki criterion, it is shown that the teleportation scheme
obtained by replacing the quantum channel (Bell state) of the usual
teleportation scheme by a quasi Bell state is optimal. Further, the performance
of various quasi Bell states as teleportation channel is compared in an ideal
situation (i.e., in the absence of noise) and under different noise models
(e.g., amplitude and phase damping channels). It is observed that the best
choice of the quasi Bell state depends on the amount non-orthogonality, both in
noisy and noiseless case. A specific quasi Bell state, which was found to be
maximally entangled in the ideal conditions, is shown to be less efficient as a
teleportation channel compared to other quasi Bell states in particular cases
when subjected to noisy channels. It has also been observed that usually the
value of average fidelity falls with an increase in the number of qubits
exposed to noisy channels (viz., Alice's, Bob's and to be teleported qubits),
but the converse may be observed in some particular cases.Comment: 14 pages, 4 figure
Bipartite and Multipartite Entanglement of Gaussian States
In this chapter we review the characterization of entanglement in Gaussian
states of continuous variable systems. For two-mode Gaussian states, we discuss
how their bipartite entanglement can be accurately quantified in terms of the
global and local amounts of mixedness, and efficiently estimated by direct
measurements of the associated purities. For multimode Gaussian states endowed
with local symmetry with respect to a given bipartition, we show how the
multimode block entanglement can be completely and reversibly localized onto a
single pair of modes by local, unitary operations. We then analyze the
distribution of entanglement among multiple parties in multimode Gaussian
states. We introduce the continuous-variable tangle to quantify entanglement
sharing in Gaussian states and we prove that it satisfies the
Coffman-Kundu-Wootters monogamy inequality. Nevertheless, we show that pure,
symmetric three-mode Gaussian states, at variance with their discrete-variable
counterparts, allow a promiscuous sharing of quantum correlations, exhibiting
both maximum tripartite residual entanglement and maximum couplewise
entanglement between any pair of modes. Finally, we investigate the connection
between multipartite entanglement and the optimal fidelity in a
continuous-variable quantum teleportation network. We show how the fidelity can
be maximized in terms of the best preparation of the shared entangled resources
and, viceversa, that this optimal fidelity provides a clearcut operational
interpretation of several measures of bipartite and multipartite entanglement,
including the entanglement of formation, the localizable entanglement, and the
continuous-variable tangle.Comment: 21 pages, 4 figures, WS style. Published as Chapter 1 in the book
"Quantum Information with Continuous Variables of Atoms and Light" (Imperial
College Press, 2007), edited by N. Cerf, G. Leuchs, and E. Polzik. Details of
the book available at http://www.icpress.co.uk/physics/p489.html . For recent
follow-ups see quant-ph/070122
Optimal conclusive teleportation of a d-dimensional unknown state
We formulate a conclusive teleportation protocol for a system in
d-dimensional Hilbert space utilizing the positive operator valued measurement
at the sending station. The conclusive teleportation protocol ensures some
perfect teleportation events when the channel is only partially entangled, at
the expense of lowering the overall average fidelity. We find the change of the
fidelity as optimizing the conclusive teleportation events and discuss how much
information remains in the inconclusive parts of the teleportation.Comment: 7 pages, 1 figure; figure correcte
Probabilistic Quantum Teleportation via 3-Qubit Non-Maximally Entangled GHZ State by Repeated Generalized Measurements
We propose a scheme of repeated generalized Bell state measurement (GBSM) for
probabilistic quantum teleportation of single qubit state of a particle (say,
0) using 3-qubit non-maximally entangled (NME) GHZ state as a quantum channel.
Alice keeps two qubits (say, 1 and 2) of the 3-qubit resource and the third
qubit (say, 3) goes to Bob. Initially, Alice performs GBSM on qubits 0 and 1
which may lead to either success or failure. On obtaining success, Alice
performs projective measurement on qubit 2 in the eigen basis of .
Both these measurement outcomes are communicated to Bob classically, which
helps him to perform a suitable unitary transformation on qubit 3 to recover
the information state. On the other hand, if failure is obtained, the next
attempt of GBSM is performed on qubits 0 and 2. This process of repeating GBSM
on alternate pair of qubits may continue until perfect teleportation with unit
fidelity is achieved. We have obtained analytical expressions for success
probability up to three repetitions of GBSM. The success probability is shown
to be a polynomial function of bipartite concurrence of the NME resource. The
variation of success probability with the bipartite concurrence has been
plotted which shows the convergence of success probability to unity with GBSM
repetitions.Comment: 11 pages, 5figure
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