2,380 research outputs found
Optimal fidelity of teleportation of coherent states and entanglement
We study the Braunstein-Kimble protocol for the continuous variable
teleportation of a coherent state. We determine lower and upper bounds for the
optimal fidelity of teleportation, maximized over all local Gaussian operations
for a given entanglement of the two-mode Gaussian state shared by the sender
(Alice) and the receiver (Bob). We also determine the optimal local
transformations at Alice and Bob sites and the corresponding maximum fidelity
when one restricts to local trace-preserving Gaussian completely positive maps.Comment: 10 pages, 2 figure
Kondo effect of Co adatoms on Ag monolayers on noble metal surfaces
The Kondo temperature of single Co adatoms on monolayers of Ag on Cu
and Au(111) is determined using Scanning Tunneling Spectroscopy. of Co on
a single monolayer of Ag on either substrate is essentially the same as that of
Co on a homogenous Ag(111) crystal. This gives strong evidence that the
interaction of surface Kondo impurities with the substrate is very local in
nature. By comparing found for Co on Cu, Ag, and Au (111)-surfaces we
show that the energy scale of the many-electron Kondo state is insensitive to
the properties of surface states and to the energetic position of the projected
bulk band edges.Comment: 4 pages, 3 figure
Local pressure-induced metallization of a semiconducting carbon nanotube in a crossed junction
The electronic and vibrational density of states of a semiconducting carbon
nanotube in a crossed junction was investigated by elastic and inelastic
scanning tunneling spectroscopy. The strong radial compression of the nanotube
at the junction induces local metallization spatially confined to a few nm. The
local electronic modifications are correlated with the observed changes in the
radial breathing and G-band phonon modes, which react very sensitively to local
mechanical deformation. In addition, the experiments reveal the crucial
contribution of the image charges to the contact potential at nanotube-metal
interfaces
Quantum dislocations: the fate of multiple vacancies in two dimensional solid 4He
Defects are believed to play a fundamental role in the supersolid state of
4He. We have studied solid 4He in two dimensions (2D) as function of the number
of vacancies n_v, up to 30, inserted in the initial configuration at rho =
0.0765 A^-2, close to the melting density, with the exact zero temperature
Shadow Path Integral Ground State method. The crystalline order is found to be
stable also in presence of many vacancies and we observe two completely
different regimes. For small n_v, up to about 6, vacancies form a bound state
and cause a decrease of the crystalline order. At larger n_v, the formation
energy of an extra vacancy at fixed density decreases by one order of magnitude
to about 0.6 K. In the equilibrated state it is no more possible to recognize
vacancies because they mainly transform into quantum dislocations and
crystalline order is found almost independent on how many vacancies have been
inserted in the initial configuration. The one--body density matrix in this
latter regime shows a non decaying large distance tail: dislocations, that in
2D are point defects, turn out to be mobile, their number is fluctuating, and
they are able to induce exchanges of particles across the system mainly
triggered by the dislocation cores. These results indicate that the notion of
incommensurate versus commensurate state loses meaning for solid 4He in 2D,
because the number of lattice sites becomes ill defined when the system is not
commensurate. Crystalline order is found to be stable also in 3D in presence of
up to 100 vacancies
Minimal qudit code for a qubit in the phase-damping channel
Using the stabilizer formalism we construct the minimal code into a
D-dimensional Hilbert space (qudit) to protect a qubit against phase damping.
The effectiveness of this code is then studied by means of input-output
fidelity.Comment: 9 pages, 3 figures. REVTe
Quantum Coherence of Image-Potential States
The quantum dynamics of the two-dimensional image-potential states in front
of the Cu(100) surface is measured by scanning tunneling microscopy (STM) and
spectroscopy (STS). The dispersion relation and the momentum resolved
phase-relaxation time of the first image-potential state are determined from
the quantum interference patterns in the local density of states (LDOS) at step
edges. It is demonstrated that the tip-induced Stark shift does not affect the
motion of the electrons parallel to the surface.Comment: Submitted to Phys. Rev. Lett., 4 pages, 4 figures; corrected typos,
minor change
High prevalence of clonally diverse spa type t026 staphylococcus aureus contaminating rural eggshells
Purpose. The presence of Staphylococcus aureus in poultry and poultry products, including eggs, increases its potential to enter the food chain, resulting in foodborne diseases. In this context, eggshell colonization by staphylococci may represent a risk factor. This study aimed to investigate the contamination of rural eggshell by S. aureus and to characterize the key features of the isolated strains. Methodology. Antibiotic resistance was assessed by disc diffusion. Resistant isolates were analysed by PCR for the identification of associated genetic determinants of resistance. PCR was also used to screen for the presence of genes coding for toxins, namely, sea, sec, sei, sem, seo and tst. The genetic characterization was extended by means of agr locus typing and spa typing. Results. 34 S. aureus were isolated. Macrolide-and tetracycline-resistant strains were prevalent. All strains were susceptible to oxacillin, cefoxitin and trimethoprim-sulfamethoxazole. PCR screening for genes encoding enterotoxins detected several virulence patterns, which, together with spa-typing and agr-locus typing, allowed cluster analysis and the description of novel clones. Conclusion. Continuous monitoring of staphylococci is needed also in rural or natural settings. Increasing the number of samples and expanding the geographical region will be needed to further extend the significance of the study
Quantum optomechanics of a multimode system coupled via photothermal and radiation pressure force
We provide a full quantum description of the optomechanical system formed by
a Fabry-Perot cavity with a movable micro-mechanical mirror whose
center-of-mass and internal elastic modes are coupled to the driven cavity mode
by both radiation pressure and photothermal force. Adopting a quantum Langevin
description, we investigate simultaneous cooling of the micromirror elastic and
center-of-mass modes, and also the entanglement properties of the
optomechanical multipartite system in its steady state.Comment: 11 pages, 7 figure
Kondo temperature of magnetic impurities at surfaces
Based on the experimental observation, that only the close vicinity of a
magnetic impurity at metal surfaces determines its Kondo behaviour, we
introduce a simple model which explains the Kondo temperatures observed for
cobalt adatoms at the (111) and (100) surfaces of Cu, Ag, and Au. Excellent
agreement between the model and scanning tunneling spectroscopy (STS)
experiments is demonstrated. The Kondo temperature is shown to depend on the
occupation of the d-level determined by the hybridization between adatom and
substrate with a minimum around single occupancy.Comment: 4 pages, 2 figure
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