6,148 research outputs found
Coherent control of multipartite entanglement
Quantum entanglement between an arbitrary number of remote qubits is examined
analytically. We show that there is a non-probabilistic way to address in one
context the management of entanglement of an arbitrary number of mixed-state
qubits by engaging quantitative measures of entanglement and a specific
external control mechanism. Both all-party entanglement and weak inseparability
are considered. We show that for , the death of all-party entanglement
is permanent after an initial collapse. In contrast, weak inseparability can be
deterministically managed for an arbitrarily large number of qubits almost
indefinitely. Our result suggests a picture of the path that the system
traverses in the Hilbert space
Bounding the entanglement of N qubits with only four measurements
We introduce a new measure for the genuinely N-partite (all-party)
entanglement of N-qubit states using the trace distance metric, and find an
algebraic formula for the GHZ-diagonal states. We then use this formula to show
how the all-party entanglement of experimentally produced GHZ states of an
arbitrary number of qubits may be bounded with only four measurements
Local Semiconducting Transition in Armchair Carbon Nanotubes: The Effect of Periodic Bi-site Perturbation on Electronic and Transport Properties of Carbon Nanotubes
In carbon nanotubes, the most abundant defects, caused for example by
irradiation or chemisorption treatments, are small perturbing clusters, i.e.
bi-site defects, extending over both A and B sites. The relative positions of
these perturbing clusters play a crucial role in determining the electronic
properties of carbon nanotubes. Using bandstructure and electronic transport
calculations, we find out that in the case of armchair metallic nanotubes a
band gap opens up when the clusters fulfill a certain periodicity condition.
This phenomenon might be used in future nanoelectronic devices in which certain
regions of single metallic nanotubes could be turned to semiconducting ones.
Although in this work we study specifically the effect of hydrogen adatom
clusters, the phenomenon is general for different types of defects. Moreover,
we study the influence of the length and randomness of the defected region on
the electron transport through it.Comment: 5 Pages, 5 Figure
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