198 research outputs found
Entanglement Sudden Death as an Indicator of Fidelity in a Four-Qubit Cluster State
I explore the entanglement evolution of a four qubit cluster state in a
dephasing environment concentrating on the phenomenon of entanglement sudden
death (ESD). Specifically, I ask whether the onset of ESD has an effect on the
utilization of this cluster state as a means of implementing a single qubit
rotation in the measurement based cluster state model of quantum computation.
To do this I compare the evolution of the entanglement to the fidelity, a
measure of how accurately the desired state (after the measurement based
operations) is achieved. I find that ESD does not cause a change of behavior or
discontinuity in the fidelity but may indicate when the fidelity of certain
states goes to .5.Comment: 8 pages, 9 figure
Quantum entanglement
All our former experience with application of quantum theory seems to say:
{\it what is predicted by quantum formalism must occur in laboratory}. But the
essence of quantum formalism - entanglement, recognized by Einstein, Podolsky,
Rosen and Schr\"odinger - waited over 70 years to enter to laboratories as a
new resource as real as energy.
This holistic property of compound quantum systems, which involves
nonclassical correlations between subsystems, is a potential for many quantum
processes, including ``canonical'' ones: quantum cryptography, quantum
teleportation and dense coding. However, it appeared that this new resource is
very complex and difficult to detect. Being usually fragile to environment, it
is robust against conceptual and mathematical tools, the task of which is to
decipher its rich structure.
This article reviews basic aspects of entanglement including its
characterization, detection, distillation and quantifying. In particular, the
authors discuss various manifestations of entanglement via Bell inequalities,
entropic inequalities, entanglement witnesses, quantum cryptography and point
out some interrelations. They also discuss a basic role of entanglement in
quantum communication within distant labs paradigm and stress some
peculiarities such as irreversibility of entanglement manipulations including
its extremal form - bound entanglement phenomenon. A basic role of entanglement
witnesses in detection of entanglement is emphasized.Comment: 110 pages, 3 figures, ReVTex4, Improved (slightly extended)
presentation, updated references, minor changes, submitted to Rev. Mod. Phys
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