1,296 research outputs found
Study to document low thrust trajectory optimization programs HILTOP and ASTOP
Detailed documentation of the HILTOP and ASTOP computer programs is presented along with results of the analyses of the possible extension of the HILTOP program and results of an extra-ecliptic mission study performed with HILTOP
The sonic analogue of black hole radiation
A microscopic description of Hawking radiation in sonic black holes has been
recently presented (Giovanazzi S 2005 Phys. Rev. Lett. 94 061302). This exactly
solvable model is formulated in terms of one-dimensional scattering of a Fermi
gas. In this paper, the model is extended to account possible finite size
effects of a realistic geometry. The flow of particles is maintained by a
piston (i.e. an impenetrable barrier) moving slowly towards the sonic horizon.
Using existing technologies the Hawking temperature can be of order of a few
microkelvin in a realistic experiment.Comment: 14 pages, 7 figures, submitted to Journal of Physics B: Atomic,
Molecular & Optical Physic
Zero sound in triplet-correlated superfluid neutron matter
The linear response of a superfluid neutron liquid onto external vector field
is studied for the case of ^{3}P_{2}-\,^{3}F_{2} pairing. The consideration
is limited to the case when the wave-length of the perturbation is large as
compared to the coherence length in the superfluid matter and the transferred
energy is small in comparison with the gap amplitude. The obtained results are
used to analyse the collisionless phonon-like excitations of the condensate of
superfluid neutrons. In particular, we analyze the case of neutron condensation
into the state with which is conventionally considered as the
preferable one in the bulk matter of neutron stars. Zero sound (if it exists)
is found to be anisotropic and undergoes strong decrement below some
temperature threshold depending substantially on the intensity of Fermi-liquid
interactions.Comment: 16 pages, 2 figure
Number fluctuations in cold quantum gases
In ultracold gases many experiments use atom imaging as a basic observable.
The resulting image is averaged over a number of realizations and mostly only
this average is used. Only recently the noise has been measured to extract
physical information. In the present paper we investigate the quantum noise
arising in these gases at zero temperature. We restrict ourselves to the
homogeneous situation and study the fluctuations in particle number found
within a given volume in the gas, and more specifically inside a sphere of
radius . We show that zero-temperature fluctuations are not extensive and
the leading term scales with sphere radius as (or ) in
three- (or one-) dimensional systems. We calculate systematically the next term
beyond this leading order. We consider first the generic case of a compressible
superfluid. Then we investigate the whole Bose-Einstein-condensation (BEC)-BCS
crossover crossover, and in particular the limiting cases of the weakly
interacting Bose gas and of the free Fermi gas.Comment: Minor changes due to referee comment
Ginzburg-Landau Expansion and the Slope of the Upper Critical Field in Disordered Superconductors with Anisotropic Pairing
It is demonstrated that the slope of the upper critical field
in superconductors with -wave pairing drops rather
fast with concentration of normal impurities, while in superconductors with
anisotropic -wave pairing grows, and in the limit of
strong disorder is described by the known dependences of the theory of
``dirty'' superconductors. This allows to use the measurements of in
disordered superconductors to discriminate between these different types of
pairing in high-temperature and heavy-fermion superconductors.Comment: 7 pages, 5 figures, RevTeX 3.0, 4 Postscript figures attached;
Submitted to JETP Letter
Frequency dependent polarizability of small metallic grains
We study the dynamic electronic polarizability of a single nano-scale
spherical metallic grain using quantum mechanical approach. We introduce the
model for interacting electrons bound in the grain allowing us numerically to
calculate the frequency dependence of the polarizability of grains of different
sizes. We show that within this model the main resonance peak corresponding to
the surface plasmon mode is blue-shifted and some minor secondary resonances
above and below the main peak exist. We study the behavior of blue shift as a
function of grain size and compare our findings with the classical
polarizability and with other results in the literature.Comment: 8 pages, 3 figure
Single-particle and collective excitations in quantum wires made up of vertically stacked quantum dots: Zero magnetic field
We report on the theoretical investigation of the elementary electronic
excitations in a quantum wire made up of vertically stacked self-assembled
InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the
experimental setups prompt us to consider an infinitely periodic system of
two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers.
The the Bloch functions and the Hermite functions together characterize the
whole system. We then make use of the Bohm-Pines' (full) random-phase
approximation in order to derive a general nonlocal, dynamic dielectric
function. Thus developed theoretical framework is then specified to work within
a (lowest miniband and) two-subband model that enables us to scrutinize the
single-particle as well as collective responses of the system. We compute and
discuss the behavior of the eigenfunctions, band-widths, density of states,
Fermi energy, single-particle and collective excitations, and finally size up
the importance of studying the inverse dielectric function in relation with the
quantum transport phenomena. It is remarkable to notice how the variation in
the barrier- and well-widths can allow us to tailor the excitation spectrum in
the desired energy range. Given the advantage of the vertically stacked quantum
dots over the planar ones and the foreseen applications in the single-electron
devices and in the quantum computation, it is quite interesting and important
to explore the electronic, optical, and transport phenomena in such systems
Dust ion-acoustic shocks in quantum dusty pair-ion plasmas
The formation of dust ion-acoustic shocks (DIASs) in a four-component quantum
plasma whose constituents are electrons, both positive and negative ions and
immobile charged dust grains, is studied. The effects of both the dissipation
due to kinematic viscosity and the dispersion caused by the charge separation
as well as the quantum tunneling due to the Bohm potential are taken into
account. The propagation of small but finite amplitude dust ion-acoustic waves
(DIAWs) is governed by the Korteweg-de Vries-Burger (KdVB) equation which
exhibits both oscillatory and monotonic shocks depending not only on the
viscosity parameters, but also on the quantum parameter H (the ratio of the
electron plasmon to the electron Fermi energy) and the positive to negative ion
density ratio. Large amplitude stationary shocks are recovered for a Mach
number exceeding its critical value. Unlike the small amplitude shocks, quite a
smaller value of the viscosity parameter, H and the density ratio may lead to
the large amplitude monotonic shock strucutres. The results could be of
importance in astrophysical and laser produced plasmas.Comment: 15 pages, 5 figure
Unified hydrodynamics theory of the lowest Landau level
We propose a hydrodynamics theory of collective quantum Hall states, which
describes incompressible liquids, hexatic liquid crystals, a bubble solid and a
Wigner crystal states within a unified framework. The structure of the theory
is uniquely determined by the space-time symmetry, and a symmetry with respect
to static shear deformations. In agreement with recent experiments the theory
predicts two gapped collective modes for incompressible liquids. We argue that
the presence of the above two modes is a universal property of a magnetized
two-dimensional collective liquid.Comment: RevTex, 8 pages. Revised and expanded versio
Experimental Test of the Dynamical Coulomb Blockade Theory for Short Coherent Conductors
We observed the recently predicted quantum suppression of dynamical Coulomb
blockade on short coherent conductors by measuring the conductance of a quantum
point contact embedded in a tunable on-chip circuit. Taking advantage of the
circuit modularity we measured most parameters used by the theory. This allowed
us to perform a reliable and quantitative experimental test of the theory.
Dynamical Coulomb blockade corrections, probed up to the second conductance
plateau of the quantum point contact, are found to be accurately normalized by
the same Fano factor as quantum shot noise, in excellent agreement with the
theoretical predictions.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
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