7,497 research outputs found
High-fidelity linear optical quantum computing with polarization encoding
We show that the KLM scheme [Knill, Laflamme and Milburn, Nature {\bf 409},
46] can be implemented using polarization encoding, thus reducing the number of
path modes required by half. One of the main advantages of this new
implementation is that it naturally incorporates a loss detection mechanism
that makes the probability of a gate introducing a non-detected error, when
non-ideal detectors are considered, dependent only on the detector dark-count
rate and independent of its efficiency. Since very low dark-count rate
detectors are currently available, a high-fidelity gate (probability of error
of order conditional on the gate being successful) can be implemented
using polarization encoding. The detector efficiency determines the overall
success probability of the gate but does not affect its fidelity. This can be
applied to the efficient construction of optical cluster states with very high
fidelity for quantum computing.Comment: 12 pages, 7 figures. Improved construction of high-fidelity entangled
ancilla; references adde
Entropy, fidelity, and double orthogonality for resonance states in two-electron quantum dots
Resonance states of a two-electron quantum dot are studied using a
variational expansion with both real basis-set functions and complex scaling
methods. The two-electron entanglement (linear entropy) is calculated as a
function of the electron repulsion at both sides of the critical value, where
the ground (bound) state becomes a resonance (unbound) state. The linear
entropy and fidelity and double orthogonality functions are compared as methods
for the determination of the real part of the energy of a resonance. The
complex linear entropy of a resonance state is introduced using complex scaling
formalism
Entropic Effects in the Very Low Temperature Regime of Diluted Ising Spin Glasses with Discrete Couplings
We study link-diluted Ising spin glass models on the hierarchical
lattice and on a three-dimensional lattice close to the percolation threshold.
We show that previously computed zero temperature fixed points are unstable
with respect to temperature perturbations and do not belong to any critical
line in the dilution-temperature plane. We discuss implications of the presence
of such spurious unstable fixed points on the use of optimization algorithms,
and we show how entropic effects should be taken into account to obtain the
right physical behavior and critical points.Comment: 4 pages, 4 figures. A major typo error in formula (8) has been
correcte
Axisymmetric multiphase lattice Boltzmann method
A lattice Boltzmann method for axisymmetric multiphase flows is presented and
validated. The method is capable of accurately modeling flows with variable
density. We develop the classic Shan-Chen multiphase model [ Phys. Rev. E 47
1815 (1993)] for axisymmetric flows. The model can be used to efficiently
simulate single and multiphase flows. The convergence to the axisymmetric
Navier-Stokes equations is demonstrated analytically by means of a
Chapmann-Enskog expansion and numerically through several test cases. In
particular, the model is benchmarked for its accuracy in reproducing the
dynamics of the oscillations of an axially symmetric droplet and on the
capillary breakup of a viscous liquid thread. Very good quantitative agreement
between the numerical solutions and the analytical results is observed
Response of a particle in a one-dimensional lattice to an applied force: Dynamics of the effective mass
We study the behaviour of the expectation value of the acceleration of a
particle in a one-dimensional periodic potential when an external homogeneous
force is suddenly applied. The theory is formulated in terms of modified Bloch
states that include the interband mixing induced by the force. This approach
allows us to understand the behaviour of the wavepacket, which responds with a
mass that is initially the bare mass, and subsequently oscillates around the
value predicted by the effective mass. If Zener tunneling can be neglected, the
expression obtained for the acceleration of the particle is valid over
timescales of the order of a Bloch oscillation, which are of interest for
experiments with cold atoms in optical lattices. We discuss how these
oscillations can be tuned in an optical lattice for experimental detection.Comment: 15 pages, 12 figure
Orientation-dependent Casimir force arising from highly anisotropic crystals: application to Bi2Sr2CaCu2O8+delta
We calculate the Casimir interaction between parallel planar crystals of Au
and the anisotropic cuprate superconductor Bi2Sr2CaCu2O8+delta (BSCCO), with
BSCCO's optical axis either parallel or perpendicular to the crystal surface,
using suitable generalizations of the Lifshitz theory. We find that the strong
anisotropy of the BSCCO permittivity gives rise to a difference in the Casimir
force between the two orientations of the optical axis, which depends on
distance and is of order 10-20% at the experimentally accessible separations 10
to 5000 nm.Comment: 5 pages, 3 figures. Accepted for publication in Physical Review
Precision measurement of the Casimir-Lifshitz force in a fluid
The Casimir force, which results from the confinement of the quantum
mechanical zero-point fluctuations of the electromagnetic fields, has received
significant attention in recent years for its effect on micro- and nano-scale
mechanical systems. With few exceptions, experimental observations have been
limited to conductive bodies interacting separated by vacuum or air. However,
interesting phenomena including repulsive forces are expected to exist in
certain circumstances between metals and dielectrics when the intervening
medium is not vacuum. In order to better understand the effect of the Casimir
force in such situations and to test the robustness of the generalized
Casimir-Lifshitz theory, we have performed the first precision measurements of
the Casimir force between two metals immersed in a fluid. For this situation,
the measured force is attractive and is approximately 80% smaller than the
force predicted by Casimir for ideal metals in vacuum. We present experimental
results and find them to be consistent with Lifshitz's theory.Comment: 6 pages, 3 figures. (version before final publication
Biosynthesis of glycogen from uridine diphosphate glucose
originalFil: Leloir, Luis Federico. Instituto de Investigaciones BioquÃmicas Fundación Campomar; ArgentinaFil: OlavarrÃa, José M.. Instituto de Investigaciones BioquÃmicas Fundación Campomar; ArgentinaFil: Goldemberg, Sara H.. Instituto de Investigaciones BioquÃmicas Fundación Campomar; ArgentinaFil: Carminatti, Héctor. Instituto de Investigaciones BioquÃmicas Fundación Campomar; ArgentinaBlanco y negro8 páginas en pdfLFL-PI-O-ART. ArtÃculos cientÃficosUnidad documental simpleAR-HYL-201
Hubbard exciton revealed by time-domain optical spectroscopy
We use broadband ultra-fast pump-probe spectroscopy in the visible range to
study the lowest excitations across the Mott-Hubbard gap in the orbitally
ordered insulator YVO3. Separating thermal and non-thermal contributions to the
optical transients, we show that the total spectral weight of the two lowest
peaks is conserved, demonstrating that both excitations correspond to the same
multiplet. The pump-induced transfer of spectral weight between the two peaks
reveals that the low-energy one is a Hubbard exciton, i.e. a resonance or bound
state between a doublon and a holon. Finally, we speculate that the pump-driven
spin-disorder can be used to quantify the kinetic energy gain of the excitons
in the ferromagnetic phase.Comment: 5 pages and 6 figures, 9 pages and 12 figures with additional
material
- …