3,963 research outputs found
The Hubbard model on a complete graph: Exact Analytical results
We derive the analytical expression of the ground state of the Hubbard model
with unconstrained hopping at half filling and for arbitrary lattice sites.Comment: Email:[email protected]
Entanglement in the classical limit: quantum correlations from classical probabilities
We investigate entanglement for a composite closed system endowed with a
scaling property allowing to keep the dynamics invariant while the effective
Planck constant hbar_eff of the system is varied. Entanglement increases as
hbar_eff goes to 0. Moreover for sufficiently low hbar_eff the evolution of the
quantum correlations, encapsulated for example in the quantum discord, can be
obtained from the mutual information of the corresponding \emph{classical}
system. We show this behavior is due to the local suppression of path
interferences in the interaction that generates the entanglement. This behavior
should be generic for quantum systems in the classical limit.Comment: 10 pages 3 figure
Tensorial depolarization of alkali atoms by isotropic collisions with neutral hydrogen
Results. We consider the problem of isotropic collisions between an alkali
atom and neutral hydrogen. We calculate the collisional tensorial components of
general p and s-states, characterized by their effective principal quantum
number . It is found that the behaviour of the tensorial components obey
simple power laws allowing quick calculations of the depolarizing collisional
rates. As application, our results should allow a rigorous treatment of the
atomic polarization profiles of the D1 -D2 lines of alkali atoms.
Conclusions. Close coupling treatments of atomic collisions are needed to
decipher the information encoded in the polarized radiation from the Sun.
Important problems remain unresolved like the role of collisions in the
Paschen-Back conditions.Comment: Accepted for publication in A&
Tuning the interactions of spin-polarized fermions using quasi-one-dimensional confinement
The behavior of ultracold atomic gases depends crucially on the two-body
scattering properties of these systems. We develop a multichannel scattering
theory for atom-atom collisions in quasi-one-dimensional (quasi-1D) geometries
such as atomic waveguides or highly elongated traps. We apply our general
framework to the low energy scattering of two spin-polarized fermions and show
that tightly-confined fermions have infinitely strong interactions at a
particular value of the 3D, free-space p-wave scattering volume. Moreover, we
describe a mapping of this strongly interacting system of two quasi-1D fermions
to a weakly interacting system of two 1D bosons.Comment: Submitted to Phys. Rev. Let
Transverse excitations of ultracold matter waves upon propagation past abrupt waveguide changes
The propagation of ultracold atomic gases through abruptly changing waveguide
potentials is examined in the limit of non-interacting atoms. Time-independent
scattering calculations of microstructured waveguides with discontinuous
changes in the transverse harmonic binding potentials are used to mimic
waveguide perturbations and imperfections. Three basic configurations are
examined: step-like, barrier-like and well-like with waves incident in the
ground mode. At low energies, the spectra rapidly depart from single-moded,
with significant transmission and reflection of excited modes. The high-energy
limit sees 100 percent transmission, with the distribution of the transmitted
modes determined simply by the overlap of the mode wave functions and
interference.Comment: 20 pages, 7 figures, under review PR
Efficient and Effective Query Auto-Completion
Query Auto-Completion (QAC) is an ubiquitous feature of modern textual search
systems, suggesting possible ways of completing the query being typed by the
user. Efficiency is crucial to make the system have a real-time responsiveness
when operating in the million-scale search space. Prior work has extensively
advocated the use of a trie data structure for fast prefix-search operations in
compact space. However, searching by prefix has little discovery power in that
only completions that are prefixed by the query are returned. This may impact
negatively the effectiveness of the QAC system, with a consequent monetary loss
for real applications like Web Search Engines and eCommerce. In this work we
describe the implementation that empowers a new QAC system at eBay, and discuss
its efficiency/effectiveness in relation to other approaches at the
state-of-the-art. The solution is based on the combination of an inverted index
with succinct data structures, a much less explored direction in the
literature. This system is replacing the previous implementation based on
Apache SOLR that was not always able to meet the required
service-level-agreement.Comment: Published in SIGIR 202
Long range scattering resonances in strong-field seeking states of polar molecules
We present first steps toward understanding the ultracold scattering
properties of polar molecules in strong electric field-seeking states. We have
found that the elastic cross section displays a quasi-regular set of potential
resonances as a function of the electric field, which potentially offers
intimate details about the inter-molecular interaction. We illustrate these
resonances in a ``toy'' model composed of pure dipoles, and in more physically
realistic systems. To analyze these resonances, we use a simple WKB
approximation to the eigenphase, which proves both reasonably accurate and
meaningful. A general treatment of the Stark effect and dipolar interactions is
also presented
Processing and Transmission of Information
Contains research objectives.Lincoln Laboratory, Purchase Order DDL B-00306U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AFI 9(604)-520
Mesoscopic continuous and discrete channels for quantum information transfer
We study the possibility of realizing perfect quantum state transfer in
mesoscopic devices. We discuss the case of the Fano-Anderson model extended to
two impurities. For a channel with an infinite number of degrees of freedom, we
obtain coherent behavior in the case of strong coupling or in weak coupling
off-resonance. For a finite number of degrees of freedom, coherent behavior is
associated to weak coupling and resonance conditions
Wave scattering by discrete breathers
We present a theoretical study of linear wave scattering in one-dimensional
nonlinear lattices by intrinsic spatially localized dynamic excitations or
discrete breathers. These states appear in various nonlinear systems and
present a time-periodic localized scattering potential for plane waves. We
consider the case of elastic one-channel scattering, when the frequencies of
incoming and transmitted waves coincide, but the breather provides with
additional spatially localized ac channels whose presence may lead to various
interference patterns. The dependence of the transmission coefficient on the
wave number q and the breather frequency Omega_b is studied for different types
of breathers: acoustic and optical breathers, and rotobreathers. We identify
several typical scattering setups where the internal time dependence of the
breather is of crucial importance for the observed transmission properties.Comment: 17 pages, 19 figures, submitted to CHAOS (Focus Issue
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