828 research outputs found
Application of product dioids for dead token detection in interval P-time event graphs
Linear description of interval P-time event graphs using a product idempotent semiring is proposed and applied to dead token detection. The dependence of dead token on initial condition is studied using residuation theory. Finally, the relationship with the spectral theory of matrices over product semirings is discusse
Evaporative Cooling of a Guided Rubidium Atomic Beam
We report on our recent progress in the manipulation and cooling of a
magnetically guided, high flux beam of atoms. Typically
atoms per second propagate in a magnetic guide providing a
transverse gradient of 800 G/cm, with a temperature K, at an
initial velocity of 90 cm/s. The atoms are subsequently slowed down to cm/s using an upward slope. The relatively high collision rate (5 s)
allows us to start forced evaporative cooling of the beam, leading to a
reduction of the beam temperature by a factor of ~4, and a ten-fold increase of
the on-axis phase-space density.Comment: 10 pages, 8 figure
Vortex dynamics of rotating dipolar Bose-Einstein condensates
We study the influence of dipole-dipole interaction on the formation of
vortices in a rotating dipolar Bose-Einstein condensate (BEC) of Cr and
Dy atoms in quasi two-dimensional geometry. By numerically solving the
corresponding time-dependent mean-field Gross-Pitaevskii equation, we show that
the dipolar interaction enhances the number of vortices while a repulsive
contact interaction increases the stability of the vortices. Further, an
ordered vortex lattice of relatively large number of vortices is found in a
strongly dipolar BEC.Comment: 15 pages, 10 figures, 1 tabl
Quantum simulation of the Anderson Hamiltonian with an array of coupled nanoresonators: delocalization and thermalization effects
The possibility of using nanoelectromechanical systems as a simulation tool
for quantum many-body effects is explored. It is demonstrated that an array of
electrostatically coupled nanoresonators can effectively simulate the
Bose-Hubbard model without interactions, corresponding in the single-phonon
regime to the Anderson tight-binding model. Employing a density matrix
formalism for the system coupled to a bosonic thermal bath, we study the
interplay between disorder and thermalization, focusing on the delocalization
process. It is found that the phonon population remains localized for a long
time at low enough temperatures; with increasing temperatures the localization
is rapidly lost due to thermal pumping of excitations into the array, producing
in the equilibrium a fully thermalized system. Finally, we consider a possible
experimental design to measure the phonon population in the array by means of a
superconducting transmon qubit coupled to individual nanoresonators. We also
consider the possibility of using the proposed quantum simulator for realizing
continuous-time quantum walks.Comment: Replaced with new improved version. To appear in EPJ Q
Localization of a dipolar Bose-Einstein condensate in a bichromatic optical lattice
By numerical simulation and variational analysis of the Gross-Pitaevskii
equation we study the localization, with an exponential tail, of a dipolar
Bose-Einstein condensate (DBEC) of Cr atoms in a three-dimensional
bichromatic optical-lattice (OL) generated by two monochromatic OL of
incommensurate wavelengths along three orthogonal directions. For a fixed
dipole-dipole interaction, a localized state of a small number of atoms () could be obtained when the short-range interaction is not too attractive
or not too repulsive. A phase diagram showing the region of stability of a DBEC
with short-range interaction and dipole-dipole interaction is given
Free Expansion of a Weakly-interacting Dipolar Fermi Gas
We theoretically investigate a polarized dipolar Fermi gas in free expansion.
The inter-particle dipolar interaction deforms phase-space distribution in trap
and also in the expansion. We exactly predict the minimal quadrupole
deformation in the expansion for the high-temperature Maxwell-Boltzmann and
zero-temperature Thomas-Fermi gases in the Hartree-Fock and Landau-Vlasov
approaches. In conclusion, we provide a proper approach to develop the
time-of-flight method for the weakly-interacting dipolar Fermi gas and also
reveal a scaling law associated with the Liouville's theorem in the long-time
behaviors of the both gases
Scissors mode of trapped dipolar gases
We study the scissors modes of dipolar boson and fermion gases trapped in a
spherically symmetric potential. We use the harmonic oscillator states to solve
the time-dependent Gross-Pitaevskii equation for bosons and the time-dependent
Hartree-Fock equation for fermions. It is pointed out that the scissors modes
of bosons and fermions can be of quite different nature
Collapse in the nonlocal nonlinear Schr\"odinger equation
We discuss spatial dynamics and collapse scenarios of localized waves
governed by the nonlinear Schr\"{o}dinger equation with nonlocal nonlinearity.
Firstly, we prove that for arbitrary nonsingular attractive nonlocal nonlinear
interaction in arbitrary dimension collapse does not occur. Then we study in
detail the effect of singular nonlocal kernels in arbitrary dimension using
both, Lyapunoff's method and virial identities. We find that for for a
one-dimensional case, i.e. for , collapse cannot happen for nonlocal
nonlinearity. On the other hand, for spatial dimension and singular
kernel , no collapse takes place if , whereas
collapse is possible if . Self-similar solutions allow us to find
an expression for the critical distance (or time) at which collapse should
occur in the particular case of kernels. Moreover, different
evolution scenarios for the three dimensional physically relevant case of Bose
Einstein condensate are studied numerically for both, the ground state and a
higher order toroidal state with and without an additional local repulsive
nonlinear interaction. In particular, we show that presence of an additional
local repulsive term can prevent collapse in those cases
Strong coupling between single-electron tunneling and nano-mechanical motion
Nanoscale resonators that oscillate at high frequencies are useful in many
measurement applications. We studied a high-quality mechanical resonator made
from a suspended carbon nanotube driven into motion by applying a periodic
radio frequency potential using a nearby antenna. Single-electron charge
fluctuations created periodic modulations of the mechanical resonance
frequency. A quality factor exceeding 10^5 allows the detection of a shift in
resonance frequency caused by the addition of a single-electron charge on the
nanotube. Additional evidence for the strong coupling of mechanical motion and
electron tunneling is provided by an energy transfer to the electrons causing
mechanical damping and unusual nonlinear behavior. We also discovered that a
direct current through the nanotube spontaneously drives the mechanical
resonator, exerting a force that is coherent with the high-frequency resonant
mechanical motion.Comment: Main text 12 pages, 4 Figures, Supplement 13 pages, 6 Figure
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