8,035 research outputs found
Global Entanglement for Multipartite Quantum States
Based on the residual entanglement [9] (Phys. Rev. A \textbf{71}, 044301
(2005)), we present the global entanglement for a multipartite quantum state.
The measure is shown to be also obtained by the bipartite partitions of the
multipartite state. The distinct characteristic of the global entanglement is
that it consists of the sum of different entanglement contributions. The
measure can provide sufficient and necessary condition of fully separability
for pure states and be conveniently extended to mixed states by minimizing the
convex hull. To test the sufficiency of the measure for mixed states, we
evaluate the global entanglement of bound entangled states. The properties of
the measure discussed finally show the global entanglement is an entanglement
monotone.Comment: 6 page
Concurrence of superposition
The bounds on concurrence of the superposition state in terms of those of the
states being superposed are studied in this paper. The bounds on concurrence
are quite different from those on the entanglement measure based on von Neumann
entropy (Phys. Rev. Lett. 97, 100502 (2006)). In particular, a nonzero lower
bound can be provided if the states being superposed are properly constrained.Comment: 4 page
Formation of diluted IIIâV nitride thin films by N ion implantation
iluted IIIâNââVâËâ alloys were successfully synthesized by nitrogen implantation into GaAs,InP, and AlyGa1âyAs. In all three cases the fundamental band-gap energy for the ion beam synthesized IIIâNââVâËâ alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grownGaNâAs1âx and InNâPâËâalloys. In GaNâAsâËâ the highest value of x (fraction of âactiveâ substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850â°C. The highest value of x achieved in InNâPâËâ was higher, 0.012, and the NP was found to be stable to at least 850â°C. In addition, the N activation efficiency in implantedInNâPâËâ was at least a factor of 2 higher than that in GaNâAsâËâ under similar processing conditions. AlyGa1âyNâAsâËâ had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1âyNâAsâËâalloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.This work was supported by the ââPhotovoltaic Materials
Focus Areaââ in the DOE Center of Excellence for the Synthesis
and Processing of Advanced Materials, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences under U.S. Department of Energy Contract No. DE-ACO3-76SF00098. The work at UCSD was partially supported
by Midwest Research Institute under subcontractor
No. AAD-9-18668-7 from NREL
Effect of Native Defects on Optical Properties of InxGa1-xN Alloys
The energy position of the optical absorption edge and the free carrier
populations in InxGa1-xN ternary alloys can be controlled using high energy
4He+ irradiation. The blue shift of the absorption edge after irradiation in
In-rich material (x > 0.34) is attributed to the band-filling effect
(Burstein-Moss shift) due to the native donors introduced by the irradiation.
In Ga-rich material, optical absorption measurements show that the
irradiation-introduced native defects are inside the bandgap, where they are
incorporated as acceptors. The observed irradiation-produced changes in the
optical absorption edge and the carrier populations in InxGa1-xN are in
excellent agreement with the predictions of the amphoteric defect model
Reexamining the "finite-size" effects in isobaric yield ratios using a statistical abrasion-ablation model
The "finite-size" effects in the isobaric yield ratio (IYR), which are shown
in the standard grand-canonical and canonical statistical ensembles (SGC/CSE)
method, is claimed to prevent obtaining the actual values of physical
parameters. The conclusion of SGC/CSE maybe questionable for neutron-rich
nucleus induced reaction. To investigate whether the IYR has "finite-size"
effects, the IYR for the mirror nuclei [IYR(m)] are reexamined using a modified
statistical abrasion-ablation (SAA) model. It is found when the projectile is
not so neutron-rich, the IYR(m) depends on the isospin of projectile, but the
size dependence can not be excluded. In reactions induced by the very
neutron-rich projectiles, contrary results to those of the SGC/CSE models are
obtained, i.e., the dependence of the IYR(m) on the size and the isospin of the
projectile is weakened and disappears both in the SAA and the experimental
results.Comment: 5 pages and 4 figure
Effects of Residue Background Events in Direct Dark Matter Detection Experiments on the Determination of the WIMP Mass
In the earlier work on the development of a model-independent data analysis
method for determining the mass of Weakly Interacting Massive Particles (WIMPs)
by using measured recoil energies from direct Dark Matter detection experiments
directly, it was assumed that the analyzed data sets are background-free, i.e.,
all events are WIMP signals. In this article, as a more realistic study, we
take into account a fraction of possible residue background events, which pass
all discrimination criteria and then mix with other real WIMP-induced events in
our data sets. Our simulations show that, for the determination of the WIMP
mass, the maximal acceptable fraction of residue background events in the
analyzed data sets of O(50) total events is ~20%, for background windows of the
entire experimental possible energy ranges, or in low energy ranges; while, for
background windows in relatively higher energy ranges, this maximal acceptable
fraction of residue background events can not be larger than ~10%. For a WIMP
mass of 100 GeV with 20% background events in the windows of the entire
experimental possible energy ranges, the reconstructed WIMP mass and the
1-sigma statistical uncertainty are ~97 GeV^{+61%}_{-35%} (~94
GeV^{+55%}_{-33%} for background-free data sets).Comment: 27 pages, 22 eps figures; v2: revised version for publication,
references added and update
Local structures of free-standing AlâGaâËâN thin films studied by extended x-ray absorption fine structure
Local structural information for the first two atomic shells surrounding Ga atoms in free standing AlâGaâËâN alloy films has been obtained by extended x-ray absorption fine structure spectroscopy. For an AlN mole fraction ranging from 0 to 0.6, we found that the first shell GaâN bond length had only a weak composition dependence, roughly one quarter of that predicted by Vegardâs Law. In the second shell, the GaâGa bond length was significantly longer than that of GaâAl (ÎâŒ0.04â0.065âĂ
). A bond-type specific composition dependence was observed for the second shell cationâcation distances. While the composition dependence of the GaâGa bond length is âŒ70% of that predicted by Vegardâs Law, the GaâAl bond length was essentially composition independent. These results suggested that local strain in AlâGaâËâN was also accommodated by lattice distortion in the Al cation sublattice.This
work was supported by the Director, Office of Science, Of-
fice of Basic Energy Sciences, Materials Science Division of
the U.S. Department of Energy under Contract No.
DE-AC03-76SF00098. The LLO work was performed at the
UC Berkeley Integrated Materials Laboratory which was
supported in part by the National Science Foundation. C.J.G.
and M.C.R. were supported by the Australian Synchrotron
Research Program, funded by the Commonwealth of Australia
via the Major National Research Facilities Program.
SSRL was supported by the Office of Basic Energy Sciences
of the U.S. Department of Energy
Genetic consequences of postglacial colonization by the endemic Yarkand hare (Lepus yarkandensis) of the arid Tarim Basin
Diluted II-VI Oxide Semiconductors with Multiple Band Gaps
We report the realization of a new multi-band-gap semiconductor. The highly
mismatched alloy Zn1-yMnyOxTe1-x has been synthesized using the combination of
oxygen ion implantation and pulsed laser melting. Incorporation of small
quantities of isovalent oxygen leads to the formation of a narrow,
oxygen-derived band of extended states located within the band gap of the
Zn1-yMnyTe host. When only 1.3% of Te atoms is replaced with oxygen in a
Zn0.88Mn0.12Te crystal (with band gap of 2.32 eV) the resulting band structure
consists of two direct band gaps with interband transitions at ~1.77 eV and 2.7
eV. This remarkable modification of the band structure is well described by the
band anticrossing model in which the interactions between the oxygen-derived
band and the conduction band are considered. With multiple band gaps that fall
within the solar energy spectrum, Zn1-yMnyOxTe1-x is a material perfectly
satisfying the conditions for single-junction photovoltaics with the potential
for power conversion efficiencies surpassing 50%.Comment: 12 pages, 4 figure
Exact dynamics of interacting qubits in a thermal environment: Results beyond the weak coupling limit
We demonstrate an exact mapping of a class of models of two interacting
qubits in thermal reservoirs to two separate spin-bath problems. Based on this
mapping, exact numerical simulations of the qubits dynamics can be performed,
beyond the weak system-bath coupling limit. Given the time evolution of the
system, we study, in a numerically exact way, the dynamics of entanglement
between pair of qubits immersed in boson thermal baths, showing a rich
phenomenology, including an intermediate oscillatory behavior, the entanglement
sudden birth, sudden death, and revival. We find that stationary entanglement
develops between the qubits due to their coupling to a thermal environment,
unlike the isolated qubits case in which the entanglement oscillates. We also
show that the occurrence of entanglement sudden death in this model depends on
the portion of the zero and double excitation states in the subsystem initial
state. In the long-time limit, analytic expressions are presented at weak
system-bath coupling, for a range of relevant qubit parameters
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