13,397 research outputs found
Broadcasting of continuous variable entanglement
We present a scheme for broadcasting of continuous variable entanglement. We
show how an initial two-mode squeezed state of the electromagnetic field shared
by two distant parties can be broadcasted into two nonlocal bipartite entangled
states. Our protocol uses a local linear amplifier and a beam splitter at each
end. We compute the fidelity of the output entangled states and show that the
broadcasting can be implemented for a variety of input squeezed states and
amplifier phases.Comment: 4 pages, 2 eps figures, RevTe
Asymmetric broadcasting of quantum correlations
In this work, we exhaustively investigate local and
nonlocal broadcasting of entanglement as well as correlations beyond
entanglement (geometric discord) using asymmetric Pauli cloners with most
general two qubit state as the resource. We exemplify asymmetric broadcasting
of entanglement using Maximally Entangled Mixed States. We demonstrate the
variation of broadcasting range with the amount of entanglement present in the
resource state as well as with the asymmetry in the cloner. We show that it is
impossible to optimally broadcast geometric discord with the help of these
asymmetric Pauli cloning machines. We also study the problem of broadcasting of entanglement using non-maximally entangled state (NME) as
the resource. For this task, we introduce a method we call successive
broadcasting which involves application of optimal cloning
machines multiple times. We compare and contrast the performance of this method
with the application of direct optimal cloning machines. We
show that optimal cloner does a better job at broadcasting
than the successive application of cloners and the successive
method can be beneficial in the absence of cloners. We also
bring out the fundamental difference between the tasks of cloning and
broadcasting in the final part of the manuscript. We create examples to show
that there exist local unitaries which can be employed to give a better range
for broadcasting. Such unitary operations are not only economical, but also
surpass the best possible range obtained using existing cloning machines
enabling broadcasting of lesser entangled states. This result opens up a new
direction in exploration of methods to facilitate broadcasting which may
outperform the standard strategies implemented through cloning transformations.Comment: Edited sections, changed figures, to be published in Physical Review
Quantum Cloning Machines and the Applications
No-cloning theorem is fundamental for quantum mechanics and for quantum
information science that states an unknown quantum state cannot be cloned
perfectly. However, we can try to clone a quantum state approximately with the
optimal fidelity, or instead, we can try to clone it perfectly with the largest
probability. Thus various quantum cloning machines have been designed for
different quantum information protocols. Specifically, quantum cloning machines
can be designed to analyze the security of quantum key distribution protocols
such as BB84 protocol, six-state protocol, B92 protocol and their
generalizations. Some well-known quantum cloning machines include universal
quantum cloning machine, phase-covariant cloning machine, the asymmetric
quantum cloning machine and the probabilistic quantum cloning machine etc. In
the past years, much progress has been made in studying quantum cloning
machines and their applications and implementations, both theoretically and
experimentally. In this review, we will give a complete description of those
important developments about quantum cloning and some related topics. On the
other hand, this review is self-consistent, and in particular, we try to
present some detailed formulations so that further study can be taken based on
those results.Comment: 98 pages, 12 figures, 400+ references. Physics Reports (published
online
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