6 research outputs found
Long Distance Entanglement Generation in 2D Networks
We consider 2D networks composed of nodes initially linked by two-qubit mixed
states. In these networks we develop a global error correction scheme that can
generate distance-independent entanglement from arbitrary network geometries
using rank two states. By using this method and combining it with the concept
of percolation we also show that the generation of long distance entanglement
is possible with rank three states. Entanglement percolation and global error
correction have different advantages depending on the given situation. To
reveal the trade-off between them we consider their application on networks
containing pure states. In doing so we find a range of pure-state schemes, each
of which has applications in particular circumstances: For instance, we can
identify a protocol for creating perfect entanglement between two distant
nodes. However, this protocol can not generate a singlet between any two nodes.
On the other hand, we can also construct schemes for creating entanglement
between any nodes, but the corresponding entanglement fidelity is lower.Comment: 10 pages, 9 figures, 1 tabl
The Optical Excitation of Zigzag Carbon Nanotubes with Photons Guided in Nanofibers
We consider the excitation of electrons in semiconducting carbon nanotubes by
photons from the evanescent field created by a subwavelength-diameter optical
fiber. The strongly changing evanescent field of such nanofibers requires
dropping the dipole approximation. We show that this leads to novel effects,
especially a high dependence of the photon absorption on the relative
orientation and geometry of the nanotube-nanofiber setup in the optical and
near infrared domain. In particular, we calculate photon absorption
probabilities for a straight nanotube and nanofiber depending on their relative
angle. Nanotubes orthogonal to the fiber are found to perform much better than
parallel nanotubes when they are short. As the nanotube gets longer the
absorption of parallel nanotubes is found to exceed the orthogonal nanotubes
and approach 100% for extremely long nanotubes. In addition, we show that if
the nanotube is wrapped around the fiber in an appropriate way the absorption
is enhanced. We find that optical and near infrared photons could be converted
to excitations with efficiencies that may exceed 90%. This may provide
opportunities for future photodetectors and we discuss possible setups.Comment: 14 pages, 14 figure
Singlet Generation in Mixed State Quantum Networks
We study the generation of singlets in quantum networks with nodes initially
sharing a finite number of partially entangled bipartite mixed states. We prove
that singlets between arbitrary nodes in such networks can be created if and
only if the initial states connecting the nodes have a particular form. We then
generalize the method of entanglement percolation, previously developed for
pure states, to mixed states of this form. As part of this, we find and compare
different distillation protocols necessary to convert groups of mixed states
shared between neighboring nodes of the network into singlets. In addition, we
discuss protocols that only rely on local rules for the efficient connection of
two remote nodes in the network via entanglement swapping. Further improvements
of the success probability of singlet generation are developed by using
particular forms of `quantum preprocessing' on the network. This includes
generalized forms of entanglement swapping and we show how such strategies can
be embedded in regular and hierarchical quantum networks.Comment: 17 pages, 21 figure
Entanglement Percolation with Bipartite Mixed States
We develop a concept of entanglement percolation for long-distance singlet
generation in quantum networks with neighboring nodes connected by partially
entangled bipartite mixed states. We give a necessary and sufficient condition
on the class of mixed network states for the generation of singlets. States
beyond this class are insufficient for entanglement percolation. We find that
neighboring nodes are required to be connected by multiple partially entangled
states and devise a rich variety of distillation protocols for the conversion
of these states into singlets. These distillation protocols are suitable for a
variety of network geometries and have a sufficiently high success probability
even for significantly impure states. In addition to this, we discuss possible
further improvements achievable by using quantum strategies including
generalized forms of entanglement swapping.Comment: 6+ pages, 5 figures; Published versio
Singlet generation in mixed-state quantum networks
We study the generation of singlets in quantum networks with nodes initially sharing a finite number of partially entangled bipartite mixed states. We prove that singlets between arbitrary nodes in such networks can be created if and only if the initial states connecting the nodes have a particular form. We then generalize the method of entanglement percolation, previously developed for pure states, to mixed states of this form. As part of this, we find and compare different distillation protocols necessary to convert groups of mixed states shared between neighboring nodes of the network into singlets. In addition, we discuss protocols that only rely on local rules for the efficient connection of two remote nodes in the network via entanglement swapping. Further improvements of the success probability of singlet generation are developed by using particular forms of "quantum preprocessing" on the network. This includes generalized forms of entanglement swapping and we show how such strategies can be embedded in regular and hierarchical quantum networks. © 2010 The American Physical Society