2,365 research outputs found
Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling
We have studied electronic conductivity and shot noise of bilayer graphene
(BLG) sheets at high bias voltages and low bath temperature K. As a
function of bias, we find initially an increase of the differential
conductivity, which we attribute to self-heating. At higher bias, the
conductivity saturates and even decreases due to backscattering from optical
phonons. The electron-phonon interactions are also responsible for the decay of
the Fano factor at bias voltages V. The high bias electronic
temperature has been calculated from shot noise measurements, and it goes up to
K at V. Using the theoretical temperature dependence of BLG
conductivity, we extract an effective electron-optical phonon scattering time
. In a 230 nm long BLG sample of mobility
cmVs, we find that decreases with increasing
voltage and is close to the charged impurity scattering time fs
at V.Comment: 7 pages, 7 figures. Extended version of the high bias part of version
1. The low bias part is discussed in arXiv:1102.065
Efficient single-photon emission from electrically driven InP quantum dots epitaxially grown on Si(001)
The heteroepitaxy of III-V semiconductors on silicon is a promising approach
for making silicon a photonic platform for on-chip optical interconnects and
quantum optical applications. Monolithic integration of both material systems
is a long-time challenge, since different material properties lead to high
defect densities in the epitaxial layers. In recent years, nanostructures
however have shown to be suitable for successfully realising light emitters on
silicon, taking advantage of their geometry. Facet edges and sidewalls can
minimise or eliminate the formation of dislocations, and due to the reduced
contact area, nanostructures are little affected by dislocation networks. Here
we demonstrate the potential of indium phosphide quantum dots as efficient
light emitters on CMOS-compatible silicon substrates, with luminescence
characteristics comparable to mature devices realised on III-V substrates. For
the first time, electrically driven single-photon emission on silicon is
presented, meeting the wavelength range of silicon avalanche photo diodes'
highest detection efficiency
Influence of anodizing process on fatigue life of a machined aluminium alloy
In order to investigate the coupled effects of machining and anodizing processes on fatigue life of alloy 7010-T7451, a series of rotating bending fatigue tests were conducted at 60Hz. In the as machined condition, test results showed that fatigue life is surface roughness dependent and that fatigue life decreases with an increase in surface roughness and this effect is found to be more pronounced in high cycle fatigue where major portion of fatigue life is consumed in nucleating the cracks. Effects of pretreatments, like degreasing and pickling employed prior to anodizing, on fatigue life of the given alloy were also studied. Results demonstrated that degreasing showed no change in fatigue life while pickling had negative impact on fatigue life of specimens. The small decrease in fatigue life of anodized specimens as compare to pickled specimens is attributed to brittle and microcracking of the coating. Scanning electron microscopic (SEM) examination revealed multi-site crack initiation for the pickled and anodized specimens. SEM examination showed that pickling solution attacked the grain boundaries and intermetallic inclusions present on the surface resulting in pits formation. These pits are of primary concern with respect to accelerated fatigue crack nucleation and subsequent anodized coating formation
Reconstruction of the optical potential from scattering data
We propose a method for reconstruction of the optical potential from
scattering data. The algorithm is a two-step procedure. In the first step the
real part of the potential is determined analytically via solution of the
Marchenko equation. At this point we use a diagonal Pad\'{e} approximant of the
corresponding unitary -matrix. In the second step the imaginary part of the
potential is determined via the phase equation of the variable phase approach.
We assume that the real and the imaginary parts of the optical potential are
proportional. We use the phase equation to calculate the proportionality
coefficient. A numerical algorithm is developed for a single and for coupled
partial waves. The developed procedure is applied to analysis of
, , and data.Comment: 26 pages, 8 figures, results of nucl-th/0410092 are refined, some new
results are presente
Increasing complexity with quantum physics
We argue that complex systems science and the rules of quantum physics are
intricately related. We discuss a range of quantum phenomena, such as
cryptography, computation and quantum phases, and the rules responsible for
their complexity. We identify correlations as a central concept connecting
quantum information and complex systems science. We present two examples for
the power of correlations: using quantum resources to simulate the correlations
of a stochastic process and to implement a classically impossible computational
task.Comment: 22 pages, 4 figure
ORGANIC FACIES EVOLUTION OF NEOGENE AND QUARTERNARY SEDIMENTS FROM THE NORWEGIAN SEA (ODP LEG 104 / VØRING PLATEAU)
Pulsar Searches with the SKA
The Square Kilometre Array will be an amazing instrument for pulsar
astronomy. While the full SKA will be sensitive enough to detect all pulsars in
the Galaxy visible from Earth, already with SKA1, pulsar searches will discover
enough pulsars to increase the currently known population by a factor of four,
no doubt including a range of amazing unknown sources. Real time processing is
needed to deal with the 60 PB of pulsar search data collected per day, using a
signal processing pipeline required to perform more than 10 POps. Here we
present the suggested design of the pulsar search engine for the SKA and
discuss challenges and solutions to the pulsar search venture.Comment: 4 pages, 1 figure. To be published in Proceedings of IAU Symposium
337: Pulsar Astrophysics - The Next 50 Year
How to share a quantum secret
We investigate the concept of quantum secret sharing. In a ((k,n)) threshold
scheme, a secret quantum state is divided into n shares such that any k of
those shares can be used to reconstruct the secret, but any set of k-1 or fewer
shares contains absolutely no information about the secret. We show that the
only constraint on the existence of threshold schemes comes from the quantum
"no-cloning theorem", which requires that n < 2k, and, in all such cases, we
give an efficient construction of a ((k,n)) threshold scheme. We also explore
similarities and differences between quantum secret sharing schemes and quantum
error-correcting codes. One remarkable difference is that, while most existing
quantum codes encode pure states as pure states, quantum secret sharing schemes
must use mixed states in some cases. For example, if k <= n < 2k-1 then any
((k,n)) threshold scheme must distribute information that is globally in a
mixed state.Comment: 5 pages, REVTeX, submitted to PR
The Uncertainty Principle in the Presence of Quantum Memory
The uncertainty principle, originally formulated by Heisenberg, dramatically
illustrates the difference between classical and quantum mechanics. The
principle bounds the uncertainties about the outcomes of two incompatible
measurements, such as position and momentum, on a particle. It implies that one
cannot predict the outcomes for both possible choices of measurement to
arbitrary precision, even if information about the preparation of the particle
is available in a classical memory. However, if the particle is prepared
entangled with a quantum memory, a device which is likely to soon be available,
it is possible to predict the outcomes for both measurement choices precisely.
In this work we strengthen the uncertainty principle to incorporate this case,
providing a lower bound on the uncertainties which depends on the amount of
entanglement between the particle and the quantum memory. We detail the
application of our result to witnessing entanglement and to quantum key
distribution.Comment: 5 pages plus 12 of supplementary information. Updated to match the
journal versio
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