1,020 research outputs found
Extended Bose Hubbard model of interacting bosonic atoms in optical lattices: from superfluidity to density waves
For systems of interacting, ultracold spin-zero neutral bosonic atoms,
harmonically trapped and subject to an optical lattice potential, we derive an
Extended Bose Hubbard (EBH) model by developing a systematic expansion for the
Hamiltonian of the system in powers of the lattice parameters and of a scale
parameter, the {\it lattice attenuation factor}. We identify the dominant terms
that need to be retained in realistic experimental conditions, up to
nearest-neighbor interactions and nearest-neighbor hoppings conditioned by the
on site occupation numbers. In mean field approximation, we determine the free
energy of the system and study the phase diagram both at zero and at finite
temperature. At variance with the standard on site Bose Hubbard model, the zero
temperature phase diagram of the EBH model possesses a dual structure in the
Mott insulating regime. Namely, for specific ranges of the lattice parameters,
a density wave phase characterizes the system at integer fillings, with domains
of alternating mean occupation numbers that are the atomic counterparts of the
domains of staggered magnetizations in an antiferromagnetic phase. We show as
well that in the EBH model, a zero-temperature quantum phase transition to pair
superfluidity is in principle possible, but completely suppressed at lowest
order in the lattice attenuation factor. Finally, we determine the possible
occurrence of the different phases as a function of the experimentally
controllable lattice parameters.Comment: 18 pages, 7 figures, accepted for publication in Phys. Rev.
Massive Quantum Memories by Periodically Inverted Dynamic Evolutions
We introduce a general scheme to realize perfect quantum state reconstruction
and storage in systems of interacting qubits. This novel approach is based on
the idea of controlling the residual interactions by suitable external controls
that, acting on the inter-qubit couplings, yield time-periodic inversions in
the dynamical evolution, thus cancelling exactly the effects of quantum state
diffusion. We illustrate the method for spin systems on closed rings with XY
residual interactions, showing that it enables the massive storage of
arbitrarily large numbers of local states, and we demonstrate its robustness
against several realistic sources of noise and imperfections.Comment: 10 pages, 3 figures. Contribution to the Proceedings of the Workshop
on "Quantum entanglement in physical and information sciences", held in Pisa,
December 14-18, 200
Influence of trapping potentials on the phase diagram of bosonic atoms in optical lattices
We study the effect of external trapping potentials on the phase diagram of
bosonic atoms in optical lattices. We introduce a generalized Bose-Hubbard
Hamiltonian that includes the structure of the energy levels of the trapping
potential, and show that these levels are in general populated both at finite
and zero temperature. We characterize the properties of the superfluid
transition for this situation and compare them with those of the standard
Bose-Hubbard description. We briefly discuss similar behaviors for fermionic
systems.Comment: 4 pages, 3 figures; final version, to be published in Phys. Rev.
Resolved CO(1-0) Nuclei in IRAS 14348-1447: Evidence for Massive Bulge Progenitors to Ultraluminous Infrared Galaxies
High-resolution, CO(1-0) interferometry of the ultraluminous infrared galaxy
IRAS 14348-1447 is presented. The merger system has a molecular gas mass of
\~3x10^10 solar masses and a projected nuclear separation of 4.8 kpc (3.5"),
making it one of the most molecular gas-rich galaxies known and an ideal
candidate for studying the intermediate stages of an ultraluminous merger
event. The CO morphology shows two molecular gas components associated with the
stellar nuclei of the progenitors, consistent with the idea that the molecular
disks are gravitationally bound by the dense bulges of the progenitor galaxies
as the interaction proceeds. In contrast, less luminous infrared galaxies
observed to date with projected nuclear separations of ~<5 kpc show a dominant
CO component between the stellar nuclei. This discrepancy may be an indication
that the progenitors of mergers with lower infrared luminosity do not possess
massive bulges, and that the gas is stripped during the initial encounter of
their progenitors. A comparison of the CO and radio luminosities of the NE and
SW component show them to have comparable radio and CO flux ratios of
f(NE)/f(SW) ~0.6, possibly indicating that the amount of star-forming molecular
gas in the progenitors is correlated with the supernovae rate. The estimate of
molecular gas masses of the nuclei and the extent of the radio emission are
used to infer that the nuclei of IR 14348-1447 have gas densities comparable to
the cores of elliptical galaxies.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in
pres
Testing a double AGN hypothesis for Mrk 273
The ULIRG Mrk 273 contains two infrared nuclei, N and SW, separated by 1
arcsec. A Chandra observation has identified the SW nucleus as an absorbed
X-ray source with nH ~4e23 cm-2 but also hinted at the possible presence of a
Compton thick AGN in the N nucleus, where a black hole of 10^9 Msun is inferred
from the ionized gas kinematics. The intrinsic X-ray spectral slope recently
measured by NuSTAR is unusually hard (photon index of ~1.3) for a Seyfert
nucleus, for which we seek an alternative explanation. We hypothesise a
strongly absorbed X-ray source in N, of which X-ray emission rises steeply
above 10 keV, in addition to the known X-ray source in SW, and test it against
the NuSTAR data, assuming the standard spectral slope (photon index of 1.9).
This double X-ray source model gives a good explanation of the hard continuum
spectrum, the deep Fe K absorption edge, and the strong Fe K line observed in
this ULIRG, without invoking the unusual spectral slope required for a single
source interpretation. The putative X-ray source in N is found to be absorbed
by nH = 1.4(+0.7/-0.4)e24 cm-2. The estimated 2-10 keV luminosity of the N
source is 1.3e43 erg/s, about a factor of 2 larger than that of SW during the
NuSTAR observation. Uncorrelated variability above and below 10 keV between the
Suzaku and NuSTAR observations appears to support the double source
interpretation. Variability in spectral hardness and Fe K line flux between the
previous X-ray observations is also consistent with this picture.Comment: 6 pages, 5 figures, Accepted for publication in A&
Nonlinear quantum model for atomic Josephson junctions with one and two bosonic species
We study atomic Josephson junctions (AJJs) with one and two bosonic species
confined by a double-well potential. Proceeding from the second quantized
Hamiltonian, we show that it is possible to describe the zero-temperature AJJs
microscopic dynamics by means of extended Bose-Hubbard (EBH) models, which
include usually-neglected nonlinear terms. Within the mean-field approximation,
the Heisenberg equations derived from such two-mode models provide a
description of AJJs macroscopic dynamics in terms of ordinary differential
equations (ODEs). We discuss the possibility to distinguish the Rabi,
Josephson, and Fock regimes, in terms of the macroscopic parameters which
appear in the EBH Hamiltonians and, then, in the ODEs. We compare the
predictions for the relative populations of the Bose gases atoms in the two
wells obtained from the numerical solutions of the two-mode ODEs, with those
deriving from the direct numerical integration of the Gross-Pitaevskii
equations (GPEs). Our investigations shows that the nonlinear terms of the ODEs
are crucial to achieve a good agreement between ODEs and GPEs approaches, and
in particular to give quantitative predictions of the self-trapping regime.Comment: Accepted for the publication in J. Phys. B: At. Mol. Opt. Phy
Evidences for a quasi 60-year North Atlantic Oscillation since 1700 and its meaning for global climate change
The North Atlantic Oscillation (NAO) obtained using instrumental and
documentary proxy predictors from Eurasia is found to be characterized by a
quasi 60-year dominant oscillation since 1650. This pattern emerges clearly
once the NAO record is time integrated to stress its comparison with the
temperature record. The integrated NAO (INAO) is found to well correlate with
the length of the day (since 1650) and the global surface sea temperature
record HadSST2 and HadSST3 (since 1850). These findings suggest that INAO can
be used as a good proxy for global climate change, and that a 60-year cycle
exists in the global climate since at least 1700. Finally, the INAO ~60-year
oscillation well correlates with the ~60- year oscillations found in the
historical European aurora record since 1700, which suggests that this 60-year
dominant climatic cycle has a solar-astronomical origin
A Molecular Tidal Tail in the Medusa Minor Merger
We have detected CO 1-0 emission along the tidal tail of the NGC 4194 (the
Medusa) merger. It is the first CO detection in the optical tail of a minor
merger. Emission is detected both in the centre of the tail and at its tip. The
molecular mass in the 33'' Onsala 20m beam is estimated to be >= 8.5 x 10^7
M_{sun} which is at least 4% of the total molecular mass measured so far in
this system. We suggest that the emission is a molecular tidal tail which is
part of the extended structure of the main body, and that the molecular gas was
thrown out by the collision instead of having formed in situ from condensing
atomic material. We find it unlikely that the emission is associated with a
tidal dwarf galaxy (even if the future formation of such an object is
possible), but high resolution HI, CO and optical observations are necessary to
resolve the issue. The Medusa is very likely the result of an elliptical+spiral
collison and our detection supports the notion that molecular gas in minor
mergers can be found at great distances from the merger centre.Comment: 4 Pages, 2 figures included, accepted for A&A letter
The location of an active nucleus and a shadow of a tidal tail in the ULIRG Mrk 273
Analysis of data from the Chandra X-ray Observatory for the double nucleus ULIRG Mrk 273 reveals an absorbed hard X-ray source coincident with the southwest nucleus, implying that this unresolved, near-infrared source is where an active nucleus resides, while the northern nuclear region contains a powerful starburst that dominates the far infrared luminosity. There is evidence of a slight image extension in the 6–7 keV band, where an Fe K line is present, towards the northern nucleus. A large-scale, diffuse emission nebula detected in soft X-rays contains a dark lane that spatially coincides with a high surface-brightness tidal tail extending ~50 arcsec (40 kpc) to the south. The soft X-ray source is likely located behind the tidal tail, which absorbs X-ray photons along the line of sight. The estimated column density of cold gas in the tidal tail responsible for shadowing the soft X-rays is N_H ≥ 6 × 10^(21) cm^(-2), consistent with the tidal tail having an edge-on orientation
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