877 research outputs found
Driven Rydberg atoms reveal quartic level repulsion
The dynamics of Rydberg states of a hydrogen atom subject simultaneously to
uniform static electric field and two microwave fields with commensurate
frequencies is considered in the range of small fields amplitudes. In the
certain range of the parameters of the system the classical secular motion of
the electronic ellipse reveals chaotic behavior. Quantum mechanically, when the
fine structure of the atom is taken into account, the energy level statistics
obey predictions appropriate for the symplectic Gaussian random matrix
ensemble.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let
Plant structural complexity and mechanical defenses mediate predator-prey interactions in an odonate-bird system.
Habitat-forming species provide refuges for a variety of associating species; these refuges may mediate interactions between species differently depending on the functional traits of the habitat-forming species. We investigated refuge provisioning by plants with different functional traits for dragonfly and damselfly (Odonata: Anisoptera and Zygoptera) nymphs emerging from water bodies to molt into their adult stage. During this period, nymphs experience high levels of predation by birds. On the shores of a small pond, plants with mechanical defenses (e.g., thorns and prickles) and high structural complexity had higher abundances of odonate exuviae than nearby plants which lacked mechanical defenses and exhibited low structural complexity. To disentangle the relative effects of these two potentially important functional traits on nymph emergence-site preference and survival, we conducted two fully crossed factorial field experiments using artificial plants. Nymphs showed a strong preference for artificial plants with high structural complexity and to a lesser extent, mechanical defenses. Both functional traits increased nymph survival but through different mechanisms. We suggest that future investigations attempt to experimentally separate the elements contributing to structural complexity to elucidate the mechanistic underpinnings of refuge provisioning
Many-body Anderson localization in one dimensional systems
We show, using quasi-exact numerical simulations, that Anderson localization
of one-dimensional particles in a disordered potential survives in the presence
of attractive interaction between particles. The localization length of the
composite particle can be computed analytically for weak disorder and is in
good agreement with the quasi-exact numerical observations using Time Evolving
Block Decimation. Our approach allows for simulation of the entire experiment
including the final measurement of all atom positions.Comment: 12pp, 5 fig, version accepted in NJ
Dark soliton in a disorder potential
We consider dark soliton in a Bose-Einstein condensate in the presence of a
weak disorder potential. Deformation of the soliton shape is analyzed within
the Bogoliubov approach and by employing expansion in eigenstates of the
P\"oschl-Teller Hamiltonian. Comparison of the results with the numerical
simulations indicates that the linear response analysis reveals good agreement
even if the strength of the disorder is of the order of the chemical potential
of the system. In the second part of the paper we concentrate on quantum nature
of the dark soliton and demonstrate that the soliton may reveal Anderson
localization in the presence of a disorder. The Anderson localized soliton may
decay due to quasi-particle excitations induced by the disorder. However, we
show that the corresponding lifetime is much longer than condensate lifetime in
a typical experiment.Comment: 10 pages, 3 figures, version accepted for publication in Phys. Rev.
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