146 research outputs found
Two-dimensional discrete solitons in dipolar Bose-Einstein condensates
We analyze the formation and dynamics of bright unstaggered solitons in the
disk-shaped dipolar Bose-Einstein condensate, which features the interplay of
contact (collisional) and long-range dipole-dipole (DD) interactions between
atoms. The condensate is assumed to be trapped in a strong optical-lattice
potential in the disk's plane, hence it may be approximated by a
two-dimensional (2D) discrete model, which includes the on-site nonlinearity
and cubic long-range (DD) interactions between sites of the lattice. We
consider two such models, that differ by the form of the on-site nonlinearity,
represented by the usual cubic term, or more accurate nonpolynomial one,
derived from the underlying 3D Gross-Pitaevskii equation. Similar results are
obtained for both models. The analysis is focused on effects of the DD
interaction on fundamental localized modes in the lattice (2D discrete
solitons). The repulsive isotropic DD nonlinearity extends the existence and
stability regions of the fundamental solitons. New families of on-site,
inter-site and hybrid solitons, built on top of a finite background, are found
as a result of the interplay of the isotropic repulsive DD interaction and
attractive contact nonlinearity. By themselves, these solutions are unstable,
but they evolve into robust breathers which exist on an oscillating background.
In the presence of the repulsive contact interactions, fundamental localized
modes exist if the DD interaction (attractive isotropic or anisotropic) is
strong enough. They are stable in narrow regions close to the anticontinuum
limit, while unstable solitons evolve into breathers. In the latter case, the
presence of the background is immaterial
Vector solitons in nearly-one-dimensional Bose-Einstein condensates
We derive a system of nonpolynomial Schroedinger equations (NPSEs) for
one-dimensional wave functions of two components in a binary self-attractive
Bose-Einstein condensate loaded in a cigar-shaped trap. The system is obtained
by means of the variational approximation, starting from the coupled 3D
Gross-Pitaevskii equations and assuming, as usual, the factorization of 3D wave
functions. The system can be obtained in a tractable form under a natural
condition of symmetry between the two species. A family of vector
(two-component) soliton solutions is constructed. Collisions between orthogonal
solitons (ones belonging to the different components) are investigated by means
of simulations. The collisions are essentially inelastic. They result in strong
excitation of intrinsic vibrations in the solitons, and create a small
orthogonal component ("shadow") in each colliding soliton. The collision may
initiate collapse, which depends on the mass and velocities of the solitons.Comment: 7 pages, 6 figures; Physical Review A, in pres
Increase of efficiency of development of personal potential of students of the university in the process of sports training
The article considers pedagogical conditions of increase of efficiency of development of personal potential of students of the University in the process of sports trainingВ статье рассматриваются педагогические условия повышения эффективности развития личностного потенциала студентов университета в процессе физкультурно-спортивной подготовк
Pedagogical conditions of increase of efficiency of development of personal potential of students of the university in the process of sports training
The article considers pedagogical conditions of increase of efficiency of development of personal potential of students of the University in the process of sports trainingРассматриваются педагогические условия повышения эффективности развития личностного потенциала студентов университета в процессе физкультурно-спортивной подготовк
Modulational instability of solitary waves in non-degenerate three-wave mixing: The role of phase symmetries
We show how the analytical approach of Zakharov and Rubenchik [Sov. Phys.
JETP {\bf 38}, 494 (1974)] to modulational instability (MI) of solitary waves
in the nonlinear Schr\"oedinger equation (NLS) can be generalised for models
with two phase symmetries. MI of three-wave parametric spatial solitons due to
group velocity dispersion (GVD) is investigated as a typical example of such
models. We reveal a new branch of neck instability, which dominates the usual
snake type MI found for normal GVD. The resultant nonlinear evolution is
thereby qualitatively different from cases with only a single phase symmetry.Comment: 4 pages with figure
Solitary wave interaction in a compact equation for deep-water gravity waves
In this study we compute numerical traveling wave solutions to a compact
version of the Zakharov equation for unidirectional deep-water waves recently
derived by Dyachenko & Zakharov (2011) Furthermore, by means of an accurate
Fourier-type spectral scheme we find that solitary waves appear to collide
elastically, suggesting the integrability of the Zakharov equation.Comment: 8 pages, 5 figures, 23 references. Other author's papers can be
downloaded at http://www.lama.univ-savoie.fr/~dutykh/ . arXiv admin note:
text overlap with arXiv:1204.288
Full-field implementation of a perfect eavesdropper on a quantum cryptography system
Quantum key distribution (QKD) allows two remote parties to grow a shared
secret key. Its security is founded on the principles of quantum mechanics, but
in reality it significantly relies on the physical implementation.
Technological imperfections of QKD systems have been previously explored, but
no attack on an established QKD connection has been realized so far. Here we
show the first full-field implementation of a complete attack on a running QKD
connection. An installed eavesdropper obtains the entire 'secret' key, while
none of the parameters monitored by the legitimate parties indicate a security
breach. This confirms that non-idealities in physical implementations of QKD
can be fully practically exploitable, and must be given increased scrutiny if
quantum cryptography is to become highly secure.Comment: Revised after editorial and peer-review feedback. This version is
published in Nat. Commun. 8 pages, 6 figures, 1 tabl
Higher-order nonlinear modes and bifurcation phenomena due to degenerate parametric four-wave mixing
We demonstrate that weak parametric interaction of a fundamental beam with
its third harmonic field in Kerr media gives rise to a rich variety of families
of non-fundamental (multi-humped) solitary waves. Making a comprehensive
comparison between bifurcation phenomena for these families in bulk media and
planar waveguides, we discover two novel types of soliton bifurcations and
other interesting findings. The later includes (i) multi-humped solitary waves
without even or odd symmetry and (ii) multi-humped solitary waves with large
separation between their humps which, however, may not be viewed as bound
states of several distinct one-humped solitons.Comment: 9 pages, 17 figures, submitted to Phys. Rev.
On the question of structure of ZnO thin films formed by IBAD and subsequently implanted with silver ions
© 2018 Institute of Physics Publishing. All rights reserved. Nanocrystalline ZnO thin films with a thickness of ∼ 235 nm were synthesized by ion beam-assisted deposition (IBAD) technique using a metal target of zinc and oxygen (O2) as a reactive gas. The near-surface region of the synthesized films was subsequently implanted with 30 keV Ag+ ions in the fluence range of (0.25-1)×1017 ion/cm2 at high ion current density of 12 μA/cm2. The structure parameters and morphology of as-deposited and subsequently implanted with silver ions ZnO films were investigated by X-ray diffraction and scanning electron microscopy techniques. It was found that the as-deposited ZnO films have inhomogeneous structure, which consists of nanocrystallites and disordered amorphous phase. The nanocrystallites of the obtained ZnO thin films have values of lattice parameters higher than for a bulk ZnO. Subsequent implantation with silver ions leads to a significant radiation heating and microstress relaxation of the film as well as to an increase in the size of nanocrystallites due to the amorphous phase
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