4,337 research outputs found
How the effective boson-boson interaction works in Bose-Fermi mixtures in periodic geometries
We study mixtures of spinless bosons and not spin-polarized fermions loaded
in two dimensional optical lattices. We approach the problem of the ground
state stability within the framework of the linear response theory; by the mean
of an iterative procedure, we are able to obtain a relation for the dependence
of boson-boson effective interaction on the absolute temperature of the sample.
Proceeding from such a formula, we write down analyitical expressions for
Supersolid (SS) and Phase Separation (PS) transition temperatures, and plot the
phase diagrams
Web-based Tools -— NED VO Services
The NASA/IPAC Extragalactic Database (NED) is a thematic, web-based research facility in widespread use by scientists, educators, space missions, and observatory operations for observation planning, data analysis, discovery, and publication of research about objects beyond our Milky Way galaxy. NED is a portal into a systematic fusion of data from hundreds of sky surveys and tens of thousands of research publications. The contents and services span the entire electromagnetic spectrum from gamma rays through radio frequencies, and are continuously updated to reflect the current literature and releases of large-scale sky survey catalogs. NED has been on the Internet since 1990, growing in content, automation and services with the evolution of information technology. NED is the world‛s largest database of crossidentified extragalactic objects. As of December 2006, the system contains approximately 10 million objects and 15 million multi-wavelength cross-IDs. Over 4 thousand catalogs and published lists covering the entire electromagnetic spectrum have had their objects cross-identified or associated, with fundamental data parameters federated for convenient queries and retrieval.
This chapter describes the interoperability of NED services with other components of the Virtual Observatory (VO). Section 1 is a brief overview of the primary NED web services. Section 2 provides a tutorial for using NED services currently available through the NVO Registry. The “name resolver” provides VO portals and related internet services with celestial coordinates for objects specified by catalog identifier (name); any alias can be queried because this service is based on the source cross-IDs established by NED. All major services have been updated to provide output in VOTable (XML) format that can be accessed directly from the NED web interface or using the NVO registry. These include access to images via SIAP, Cone- Search queries, and services providing fundamental, multi-wavelength extragalactic data such as positions, redshifts, photometry and spectral energy distributions (SEDs), and sizes (all with references and uncertainties when available). Section 3 summarizes the advantages of accessing the NED “name resolver” and other NED services via the web to replace the legacy “server mode” custom data structure previously available through a function library provided only in the C programming language. Section 4 illustrates visualization via VOPlot of an SED and the spatial distribution of sources from a NED All-Sky (By Parameters) query. Section 5 describes the new NED Spectral Archive, illustrating how VOTables are being used to standardize the data and metadata as well as the physical units of spectra made available by authors of journal articles and producers of major survey archives; quick-look spectral analysis through convenient interoperability with the SpecView (STScI) Java applet is also shown. Section 6 closes with a summary of the capabilities described herein, which greatly simplify interoperability of NED with other components of the VO, enabling new opportunities for discovery, visualization, and analysis of multiwavelength data
Spontaneous symmetry breaking and collapse in bosonic Josephson junctions
We investigate an attractive atomic Bose-Einstein condensate (BEC) trapped by
a double-well potential in the axial direction and by a harmonic potential in
the transverse directions. We obtain numerically, for the first time, a quantum
phase diagram which includes all the three relevant phases of the system:
Josephson, spontaneous symmetry breaking (SSB), and collapse. We consider also
the coherent dynamics of the BEC and calculate the frequency of
population-imbalance mode in the Josephson phase and in the SSB phase up to the
collapse. We show that these phases can be observed by using ultracold vapors
of 7Li atoms in a magneto-optical trap.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Two-mode dipolar bosonic junctions
We consider a two-mode atomic Josephson junction realized with dilute dipolar
bosons confined by a double-well. We employ the two-site extended Bose-Hubbard
Hamiltonian and characterize the ground-state of this system by the Fisher
information, coherence visibility, and entanglement entropy. These quantities
are studied as functions of the interaction between bosons in different wells.
The emergence of Schroedinger-cat like state with a loss of coherence is also
commented.Comment: 9 pages, 1 figur
Effective-range signatures in quasi-1D matter waves: sound velocity and solitons
We investigate ultracold and dilute bosonic atoms under strong transverse
harmonic confinement by using a 1D modified Gross-Pitaevskii equation (1D
MGPE), which accounts for the energy dependence of the two-body scattering
amplitude within an effective-range expansion. We study sound waves and
solitons of the quasi-1D system comparing 1D MGPE results with the 1D GPE ones.
We point out that, when the finite-size nature of the interaction is taken into
account, the speed of sound and the density profiles of both dark and bright
solitons show relevant quantitative changes with respect to what predicted by
the standard 1D GPE.Comment: 13 pages, 4 figures, improved version, added a figure and two
references, to be published in J. Phys. B: At. Mol. Opt. Phy
Quantum dynamics of a binary mixture of BECs in a double well potential: an Holstein-Primakoff approach
We study the quantum dynamics of a binary mixture of Bose-Einstein
condensates (BEC) in a double-well potential starting from a two-mode
Bose-Hubbard Hamiltonian. Focussing on the regime where the number of atoms is
very large, a mapping onto a SU(2) spin problem together with a
Holstein-Primakoff transformation is performed. The quantum evolution of the
number difference of bosons between the two wells is investigated for different
initial conditions, which range from the case of a small imbalance between the
two wells to a coherent spin state. The results show an instability towards a
phase-separation above a critical positive value of the interspecies
interaction while the system evolves towards a coherent tunneling regime for
negative interspecies interactions. A comparison with a semiclassical approach
is discussed together with some implications on the experimental realization of
phase separation with cold atoms.Comment: 12 pages, 7 figures, accepted for publication in J. Phys.
Consensus for quantum networks: from symmetry to gossip iterations
This paper extends the consensus framework, widely studied in the literature on distributed computing and control algorithms, to networks of quantum systems. We define consensus situations on the basis of invariance and symmetry properties, finding four different generalizations of classical consensus states. This new viewpoint can be directly used to study consensus for probability distributions, as these can be seen as a particular case of quantum statistical states: in this light, our analysis is also relevant for classical problems. We then extend the gossip consensus algorithm to the quantum setting and prove it converges to symmetric states while preserving the expectation of permutation-invariant global observables. Applications of the framework and the algorithms to estimation and control problems on quantum networks are discussed
Quantum correlations of few dipolar bosons in a double-well trap
We consider interacting dipolar bosonic atoms at zero temperature in a
double-well potential. This system is described by the two-space-mode extended
Bose-Hubbard (EBH) Hamiltonian which includes (in addition to the familiar BH
terms) the nearest-neighbor interaction, correlated hopping and bosonic-pair
hopping. For systems with and particles we calculate analytically
both the ground state and the Fisher information, the coherence visibility, and
the entanglement entropy that characterize the correlations of the lowest
energy state. The structure of the ground state crucially depends on the
correlated hopping . On one hand we find that this process makes possible
the occurrence of Schr\"odinger-cat states even if the onsite interatomic
attraction is not strong enough to guarantee the formation of such states. On
the other hand, in the presence of a strong onsite attraction, sufficiently
large values of destroys the cat-like state in favor of a delocalized
atomic coherent state.Comment: 21 pages, 10 figures. This paper has been accepted for publication in
a festschrift issue of Journal of Low Temperature Physics in honor of Prof.
Flavio Toigo on the occasion of his 70th birthday. The paper extends our
previous results, which can be found in arXiv:1410.5321, obtained in the
absence of dipolar interactio
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