15,489 research outputs found
Optimal nonlocal multipartite entanglement concentration based on projection measurements
We propose an optimal nonlocal entanglement concentration protocol (ECP) for
multi-photon systems in a partially entangled pure state, resorting to the
projection measurement on an additional photon. One party in quantum
communication first performs a parity-check measurement on her photon in an
N-photon system and an additional photon, and then she projects the additional
photon into an orthogonal Hilbert space for dividing the original -photon
systems into two groups. In the first group, the N parties will obtain a subset
of -photon systems in a maximally entangled state. In the second group, they
will obtain some less-entangled N-photon systems which are the resource for the
entanglement concentration in the next round. By iterating the entanglement
concentration process several times, the present ECP has the maximal success
probability which is just equivalent to the entanglement of the partially
entangled state. That is, this ECP is an optimal one.Comment: 5 pages, 4 figure
Efficient multipartite entanglement purification with the entanglement link from a subspace
We present an efficient multipartite entanglement purification protocol
(MEPP) for N-photon systems in a Greenberger-Horne-Zeilinger state with
parity-check detectors. It contains two parts. One is the conventional MEPP
with which the parties can obtain a high-fidelity N-photon ensemble directly,
similar to the MEPP with controlled-not gates. The other is our recycling MEPP
in which the entanglement link is used to produce some -photon entangled
systems from entangled N'-photon subsystems (2 \leq N'<N) coming from the
instances which are just discarded in all existing conventional MEPPs. The
entangled N'-photon subsystems are obtained efficiently by measuring the
photons with potential bit-flip errors. With these two parts, the present MEPP
has a higher efficiency than all other conventional MEPPs.Comment: 17 pages, 9 figures, 2 tables. We correct the error in the address of
the author in the published version (Phys. Rev. A 84, 052312 (2011)
Conductance spectra of metallic nanotube bundles
We report a first principles analysis of electronic transport characteristics
for (n,n) carbon nanotube bundles. When n is not a multiple of 3, inter-tube
coupling causes universal conductance suppression near Fermi level regardless
of the rotational arrangement of individual tubes. However, when n is a
multiple of 3, the bundles exhibit a diversified conductance dependence on the
orientation details of the constituent tubes. The total energy of the bundle is
also sensitive to the orientation arrangement only when n is a multiple of 3.
All the transport properties and band structures can be well understood from
the symmetry consideration of whether the rotational symmetry of the individual
tubes is commensurate with that of the bundle
Nonlocal Gate Of Quantum Network Via Cavity Quantum Electrodynamics
We propose an experimentally feasible scheme to realize the nonlocal gate
between two different quantum network nodes. With an entanglement-qubit (ebit)
acts as a quantum channel, our scheme is resistive to actual environment noise
and can get high fidelity in current cavity quantum electrodynamics (C-QED)
system.Comment: 5 pages, 3 figures, 1 tabl
Semiquantum key distribution using entangled states
Recently, Boyer et al. presented a novel semiquantum key distribution
protocol [M. Boyer, D. Kenigsberg, and T. Mor, Phys. Rev. Lett. 99, 140501
(2007)], by using four quantum states, each of which is randomly prepared by Z
basis or X basis. Here we present a semiquantum key distribution protocol by
using entangled states in which quantum Alice shares a secret key with
classical Bob. We also show the protocol is secure against eavesdropping.Comment: 6 page
Verification of a localization criterion for several disordered media
We analytically compute a localization criterion in double scattering
approximation for a set of dielectric spheres or perfectly conducting disks
uniformly distributed in a spatial volume which can be either spherical or
layered. For every disordered medium, we numerically investigate a localization
criterion, and examine the influence of the system parameters on the wavelength
localization domains.Comment: 30 pages, LateX, amstex, revtex styles, 20 figure
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