7,640 research outputs found
Quantum temporal correlations and entanglement via adiabatic control of vector solitons
It is shown that optical pulses with a mean position accuracy beyond the
standard quantum limit can be produced by adiabatically expanding an optical
vector soliton followed by classical dispersion management. The proposed scheme
is also capable of entangling positions of optical pulses and can potentially
be used for general continuous-variable quantum information processing.Comment: 5 pages, 1 figure, v2: accepted by Physical Review Letters, v3: minor
editing and shortening, v4: included the submitted erratu
Effective Dielectric Tensor for Electromagnetic Wave Propagation in Random Media
We derive exact strong-contrast expansions for the effective dielectric
tensor \epeff of electromagnetic waves propagating in a two-phase composite
random medium with isotropic components explicitly in terms of certain
integrals over the -point correlation functions of the medium. Our focus is
the long-wavelength regime, i.e., when the wavelength is much larger than the
scale of inhomogeneities in the medium. Lower-order truncations of these
expansions lead to approximations for the effective dielectric constant that
depend upon whether the medium is below or above the percolation threshold. In
particular, we apply two- and three-point approximations for \epeff to a
variety of different three-dimensional model microstructures, including
dispersions of hard spheres, hard oriented spheroids and fully penetrable
spheres as well as Debye random media, the random checkerboard, and
power-law-correlated materials. We demonstrate the importance of employing
-point correlation functions of order higher than two for high
dielectric-phase-contrast ratio. We show that disorder in the microstructure
results in an imaginary component of the effective dielectric tensor that is
directly related to the {\it coarseness} of the composite, i.e., local
volume-fraction fluctuations for infinitely large windows. The source of this
imaginary component is the attenuation of the coherent homogenized wave due to
scattering. We also remark on whether there is such attenuation in the case of
a two-phase medium with a quasiperiodic structure.Comment: 40 pages, 13 figure
Ziv-Zakai Error Bounds for Quantum Parameter Estimation
I propose quantum versions of the Ziv-Zakai bounds as alternatives to the
widely used quantum Cram\'er-Rao bounds for quantum parameter estimation. From
a simple form of the proposed bounds, I derive both a "Heisenberg" error limit
that scales with the average energy and a limit similar to the quantum
Cram\'er-Rao bound that scales with the energy variance. These results are
further illustrated by applying the bound to a few examples of optical phase
estimation, which show that a quantum Ziv-Zakai bound can be much higher and
thus tighter than a quantum Cram\'er-Rao bound for states with highly
non-Gaussian photon-number statistics in certain regimes and also stay close to
the latter where the latter is expected to be tight.Comment: v1: preliminary result, 3 pages; v2: major update, 4 pages +
supplementary calculations, v3: another major update, added proof of
"Heisenberg" limit, v4: accepted by PR
Proximity Effects in Radiative Transfer
Though the dependence of near-field radiative transfer on the gap between two
planar objects is well understood, that between curved objects is still
unclear. We show, based on the analysis of the surface polariton mediated
radiative transfer between two spheres of equal radii and minimum gap ,
that the near--field radiative transfer scales as as
and as for larger values of up to the far--field limit. We
propose a modified form of the proximity approximation to predict near--field
radiative transfer between curved objects from simulations of radiative
transfer between planar surfaces.Comment: 5 journal pages, 4 figure
On the Relationship between Resolution Enhancement and Multiphoton Absorption Rate in Quantum Lithography
The proposal of quantum lithography [Boto et al., Phys. Rev. Lett. 85, 2733
(2000)] is studied via a rigorous formalism. It is shown that, contrary to Boto
et al.'s heuristic claim, the multiphoton absorption rate of a ``NOON'' quantum
state is actually lower than that of a classical state with otherwise identical
parameters. The proof-of-concept experiment of quantum lithography [D'Angelo et
al., Phys. Rev. Lett. 87, 013602 (2001)] is also analyzed in terms of the
proposed formalism, and the experiment is shown to have a reduced multiphoton
absorption rate in order to emulate quantum lithography accurately. Finally,
quantum lithography by the use of a jointly Gaussian quantum state of light is
investigated, in order to illustrate the trade-off between resolution
enhancement and multiphoton absorption rate.Comment: 14 pages, 7 figures, submitted, v2: rewritten in response to
referees' comments, v3: rewritten and extended, v4: accepted by Physical
Review
Modeling near-field radiative heat transfer from sharp objects using a general 3d numerical scattering technique
We examine the non-equilibrium radiative heat transfer between a plate and
finite cylinders and cones, making the first accurate theoretical predictions
for the total heat transfer and the spatial heat flux profile for
three-dimensional compact objects including corners or tips. We find
qualitatively different scaling laws for conical shapes at small separations,
and in contrast to a flat/slightly-curved object, a sharp cone exhibits a local
\emph{minimum} in the spatially resolved heat flux directly below the tip. The
method we develop, in which a scattering-theory formulation of thermal transfer
is combined with a boundary-element method for computing scattering matrices,
can be applied to three-dimensional objects of arbitrary shape.Comment: 5 pages, 4 figures. Corrected background information in the
introduction, results and discussion unchange
Temperature determination from the lattice gas model
Determination of temperature from experimental data has become important in
searches for critical phenomena in heavy ion collisions. Widely used methods
are ratios of isotopes (which rely on chemical and thermal equilibrium),
population ratios of excited states etc. Using the lattice gas model we propose
a new observable: where is the charge multiplicity and
is the charge of the fragmenting system. We show that the reduced multiplicity
is a good measure of the average temperature of the fragmenting system.Comment: 11 pages, 2 ps file
Decoherence of Quantum-Enhanced Timing Accuracy
Quantum enhancement of optical pulse timing accuracy is investigated in the
Heisenberg picture. Effects of optical loss, group-velocity dispersion, and
Kerr nonlinearity on the position and momentum of an optical pulse are studied
via Heisenberg equations of motion. Using the developed formalism, the impact
of decoherence by optical loss on the use of adiabatic soliton control for
beating the timing standard quantum limit [Tsang, Phys. Rev. Lett. 97, 023902
(2006)] is analyzed theoretically and numerically. The analysis shows that an
appreciable enhancement can be achieved using current technology, despite an
increase in timing jitter mainly due to the Gordon-Haus effect. The decoherence
effect of optical loss on the transmission of quantum-enhanced timing
information is also studied, in order to identify situations in which the
enhancement is able to survive.Comment: 12 pages, 4 figures, submitte
The Statistical Multifragmentation Model with Skyrme Effective Interactions
The Statistical Multifragmentation Model is modified to incorporate the
Helmholtz free energies calculated in the finite temperature Thomas-Fermi
approximation using Skyrme effective interactions. In this formulation, the
density of the fragments at the freeze-out configuration corresponds to the
equilibrium value obtained in the Thomas-Fermi approximation at the given
temperature. The behavior of the nuclear caloric curve at constant volume is
investigated in the micro-canonical ensemble and a plateau is observed for
excitation energies between 8 and 10 MeV per nucleon. A kink in the caloric
curve is found at the onset of this gas transition, indicating the existence of
a small excitation energy region with negative heat capacity. In contrast to
previous statistical calculations, this situation takes place even in this case
in which the system is constrained to fixed volume. The observed phase
transition takes place at approximately constant entropy. The charge
distribution and other observables also turn out to be sensitive to the
treatment employed in the calculation of the free energies and the fragments'
volumes at finite temperature, specially at high excitation energies. The
isotopic distribution is also affected by this treatment, which suggests that
this prescription may help to obtain information on the nuclear equation of
state
Neutron and Proton Transverse Emission Ratio Measurements and the Density Dependence of the Asymmetry Term of the Nuclear Equation of State
Recent measurements of pre-equilibrium neutron and proton transverse emission
from (112,124)Sn+(112,124)Sn reactions at 50 MeV/A have been completed at the
National Superconducting Cyclotron Laboratory. Free nucleon transverse emission
ratios are compared to those of A=3 mirror nuclei. Comparisons are made to BUU
transport calculations and conclusions concerning the density dependence of the
asymmetry term of the nuclear equation-of-state at sub-nuclear densities are
made. The double-ratio of neutron-proton ratios between two reactions is
employed as a means of reducing first-order Coulomb effects and detector
efficiency effects. Comparison to BUU model predictions indicate a density
dependence of the asymmetry energy that is closer to a form in which the
asymmety energy increases as the square root of the density for the density
region studied. A coalescent-invariant analysis is introduced as a means of
reducing suggested difficulties with cluster emission in total nucleon
emission. Future experimentation is presented
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