11,446 research outputs found
Sharp crossover from composite fermionization to phase separation in mesoscopic mixtures of ultracold bosons
We show that a two-component mixture of a few repulsively interacting
ultracold atoms in a one-dimensional trap possesses very different quantum
regimes and that the crossover between them can be induced by tuning the
interactions in one of the species. In the composite fermionization regime,
where the interactions between both components are large, none of the species
show large occupation of any natural orbital. Our results show that by
increasing the interaction in one of the species, one can reach the
phase-separated regime. In this regime, the weakly interacting component stays
at the center of the trap and becomes almost fully phase coherent, while the
strongly interacting component is displaced to the edges of the trap. The
crossover is sharp, as observed in the in the energy and the in the largest
occupation of a natural orbital of the weakly interacting species. Such a
transition is a purely mesoscopic effect which disappears for large atom
numbers.Comment: 5 pages, 3 figure
Quantum correlations and spatial localization in one-dimensional ultracold bosonic mixtures
We present the complete phase diagram for one-dimensional binary mixtures of
bosonic ultracold atomic gases in a harmonic trap. We obtain exact results with
direct numerical diagonalization for small number of atoms, which permits us to
quantify quantum many-body correlations. The quantum Monte Carlo method is used
to calculate energies and density profiles for larger system sizes. We study
the system properties for a wide range of interaction parameters. For the
extreme values of these parameters, different correlation limits can be
identified, where the correlations are either weak or strong. We investigate in
detail how the correlation evolve between the limits. For balanced mixtures in
the number of atoms in each species, the transition between the different
limits involves sophisticated changes in the one- and two-body correlations.
Particularly, we quantify the entanglement between the two components by means
of the von Neumann entropy. We show that the limits equally exist when the
number of atoms is increased, for balanced mixtures. Also, the changes in the
correlations along the transitions among these limits are qualitatively
similar. We also show that, for imbalanced mixtures, the same limits with
similar transitions exist. Finally, for strongly imbalanced systems, only two
limits survive, i.e., a miscible limit and a phase-separated one, resembling
those expected with a mean-field approach.Comment: 18 pages, 8 figure
A topological charge selection rule for phase singularities
We present an study of the dynamics and decay pattern of phase singularities
due to the action of a system with a discrete rotational symmetry of finite
order. A topological charge conservation rule is identified. The role played by
the underlying symmetry is emphasized. An effective model describing the short
range dynamics of the vortex clusters has been designed. A method to engineer
any desired configuration of clusters of phase singularities is proposed. Its
flexibility to create and control clusters of vortices is discussed.Comment: 4 pages, 3 figure
Confining Flux Tubes in a Current Algebra Approach
We describe flux tubes and their interactions in a low energy sigma model
induced by flavor symmetry breaking in
QCD. Unlike standard QCD, this model allows gauge confinement to
manifest itself in the low energy theory, which has unscreened spinor color
sources and global flux tubes. We construct the flux tubes and show how
they mediate the confinement of spinor sources. We further examine the flux
tubes' quantum stability, spectrum and interactions. We find that flux tubes
are Alice strings, despite ambiguities in defining parallel transport.
Furthermore, twisted loops of flux tube support skyrmion number, just as gauged
Alice strings form loops that support monopole charge. This model, while
phenomenologically nonviable, thus affords a perspective on both the dynamics
of confinement and on subtleties which arise for global Alice strings.Comment: 29 pages (REVTEX) plus 6 figures, two corrections in the final
section and added reference
Four-point functions and kaon decays in a minimal AdS/QCD model
We study the predictions of holographic QCD for various observable four-point
quark flavour current-current correlators. The dual 5-dimensional bulk theory
we consider is a Yang Mills theory in a slice of
spacetime with boundaries. Particular UV and IR boundary conditions
encode the spontaneous breaking of the dual 4D global chiral symmetry down to
the subgroup. We explain in detail how to calculate the 4D four-point
quark flavour current-current correlators using the 5D holographic theory,
including interactions. We use these results to investigate predictions of
holographic QCD for the rule for kaon decays and the
parameter. The results agree well in comparison with experimental data, with an
accuracy of 25% or better. The holographic theory automatically includes the
contributions of the meson resonances to the four-point correlators. The
correlators agree well in the low-momentum and high-momentum limit, in
comparison with chiral perturbation theory and perturbative QCD results,
respectively.Comment: Published version, title changed to conform with Journal format,
references and clarifying remarks added, 40 pages, 5 figure
Fermions on half-quantum vortex
The spectrum of the fermion zero modes in the vicinity of the vortex with
fractional winding number is discussed. This is inspired by the observation of
the 1/2 vortex in high-temperature superconductors (Kirtley, et al, Phys. Rev.
Lett. 76 (1996) 1336). The fractional value of the winding number leads to the
fractional value of the invariant, which describes the topology of the energy
spectrum of fermions. This results in the phenomenon of the "half-crossing":
the spectrum approaches zero but does not cross it, being captured at the zero
energy level. The similarity with the phenomenon of the fermion condensation is
discussed.Comment: In revised version the discussion is extended and 4 references are
added. The paper is accepted for publication in JETP Letters. 10 pages, LaTeX
file, 3 figures are available at
ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96004.p
Honeybee-like collective decision making in a kilobot swarm
Drawing inspiration from honeybee swarms' nest-site selection process, we
assess the ability of a kilobot robot swarm to replicate this captivating
example of collective decision-making. Honeybees locate the optimal site for
their new nest by aggregating information about potential locations and
exchanging it through their waggle-dance. The complexity and elegance of
solving this problem relies on two key abilities of scout honeybees:
self-discovery and imitation, symbolizing independence and interdependence,
respectively. We employ a mathematical model to represent this nest-site
selection problem and program our kilobots to follow its rules. Our experiments
demonstrate that the kilobot swarm can collectively reach consensus decisions
in a decentralized manner, akin to honeybees. However, the strength of this
consensus depends not only on the interplay between independence and
interdependence but also on critical factors such as swarm density and the
motion of kilobots. These factors enable the formation of a percolated
communication network, through which each robot can receive information beyond
its immediate vicinity. By shedding light on this crucial layer of complexity
--the crowding and mobility conditions during the decision-making--, we
emphasize the significance of factors typically overlooked but essential to
living systems and life itself.Comment: 19 pages, 8 figures, 6 appendix figures, 3 supplementary figure
Power, norms and institutional change in the European Union: the protection of the free movement of goods
How do institutions of the European Union change? Using an institutionalist approach, this article highlights the interplay between power, cognitive limits, and the normative order that underpins institutional settings and assesses their impact upon the process of institutional change. Empirical evidence from recent attempts to reinforce the protection of the free movement of goods in the EU suggests that, under conditions of uncertainty, actors with ambiguous preferences assess attempts at institutional change on the basis of the historically defined normative order which holds a given institutional structure together. Hence, path dependent and incremental change occurs even when more ambitious and functionally superior proposals are on offer
How to create Alice string (half-quantum vortex) in a vector Bose-Einstein condensate
We suggest a procedure how to prepare the vortex with N=1/2 winding number --
the counterpart of the Alice string -- in a Bose--Einstein condensate with
hyperfine spin F=1. Other possible vortices in Bose-condensates are also
discussed.Comment: RevTex file, 3 pages, no figures, extended version submitted to JETP
Letter
Comment on ``the Klein-Gordon Oscillator''
The different ways of description of the particle with oscillator-like
interaction are considered. The results are in conformity with the previous
paper of S. Bruce and P. Minning.Comment: LaTeX file, 5p
- âŠ