5,277 research outputs found
Self-trapping of a binary Bose-Einstein condensate induced by interspecies interaction
The problem of self-trapping of a Bose-Einstein condensate (BEC) and a binary
BEC in an optical lattice (OL) and double well (DW) is studied using the
mean-field Gross-Pitaevskii equation. For both DW and OL, permanent
self-trapping occurs in a window of the repulsive nonlinearity of the GP
equation: . In case of OL, the critical nonlinearities
and correspond to a window of chemical potentials
defining the band gap(s) of the periodic OL. The
permanent self-trapped BEC in an OL usually represents a breathing oscillation
of a stable stationary gap soliton. The permanent self-trapped BEC in a DW, on
the other hand, is a dynamically stabilized state without any stationary
counterpart. For a binary BEC with intraspecies nonlinearities outside this
window of nonlinearity, a permanent self trapping can be induced by tuning the
interspecies interaction such that the effective nonlinearities of the
components fall in the above window
Long-range interactions of hydrogen atoms in excited states. III. nS-1S interactions for n >= 3
The long-range interaction of excited neutral atoms has a number of
interesting and surprising properties, such as the prevalence of long-range,
oscillatory tails, and the emergence of numerically large can der Waals C_6
coefficients. Furthermore, the energetically quasi-degenerate nP states require
special attention and lead to mathematical subtleties. Here, we analyze the
interaction of excited hydrogen atoms in nS states (3 <= n <= 12) with
ground-state hydrogen atoms, and find that the C_6 coefficients roughly grow
with the fourth power of the principal quantum number, and can reach values in
excess of 240,000 (in atomic units) for states with n = 12. The nonretarded van
der Waals result is relevant to the distance range R << a_0/alpha, where a_0 is
the Bohr radius and alpha is the fine-structure constant. The Casimir-Polder
range encompasses the interatomic distance range a_0/alpha << R << hbar c/L,
where L is the Lamb shift energy. In this range, the contribution of
quasi-degenerate excited nP states remains nonretarded and competes with the
1/R^2 and 1/R^4 tails of the pole terms which are generated by lower-lying mP
states with 2 <= m <= n-1, due to virtual resonant emission. The dominant pole
terms are also analyzed in the Lamb shift range R >> hbar c/L. The familiar
1/R^7 asymptotics from the usual Casimir-Polder theory is found to be
completely irrelevant for the analysis of excited-state interactions. The
calculations are carried out to high precision using computer algebra in order
to handle a large number of terms in intermediate steps of the calculation, for
highly excited states.Comment: 17 pages; RevTe
Virtual Resonant Emission and Oscillatory Long-Range Tails in van der Waals Interactions of Excited States: QED Treatment and Applications
We report on a quantum electrodynamic (QED) investigation of the interaction
between a ground state atom with another atom in an excited state. General
expressions, applicable to any atom, are indicated for the long-range tails
which are due to virtual resonant emission and absorption into and from vacuum
modes whose frequency equals the transition frequency to available lower-lying
atomic states. For identical atoms, one of which is in an excited state, we
also discuss the mixing term which depends on the symmetry of the two-atom wave
function (these evolve into either the gerade or the ungerade state for close
approach), and we include all nonresonant states in our rigorous QED treatment.
In order to illustrate the findings, we analyze the fine-structure resolved van
der Waals interaction for nD-1S hydrogen interactions with n=8,10,12 and find
surprisingly large numerical coefficients.Comment: 6 pages; RevTe
Effect of Irrigation and Potash Levels on Keeping Quality of Potato
Irrigation and fertilizer are the most dominating factors, in deciding the keeping quality of potato. It is, therefore, essential to formulate the efficient, reliable and economically viable irrigation management strategy with the use of potassium nutrient in order to produce better keeping quality. The investigation comprising four levels of irrigation (25, 30, 35 and 40 mm CPE (Cumulative pan evaporation) and four levels of potash (0, 100, 125 and 150 kg/ha) was carried out at Research Farm of the Department of Vegetable Science, CCS Haryana Agricultural University, (Haryana) Hisar, India during two years to find out the optimum level of irrigation and potash for obtaining higher yield of potatoes with better keeping quality at ambient room temperature. The potato variety used for the investigation was Kufri Bahar. The treatments were laid out in a split plot design with three replications. The increasing levels of irrigation and potash showed significant improvement in keeping quality parameters of potato. Likewise, the values for physiological loss in weight and decay loss of potato tubers (%) at 15, 30, 45 and 60 days after harvest were the lowest with irrigation level 40 mm CPE and application of potash @ 150 kg/ha. The two years results suggest that the irrigation level 40 mm CPE along with potash @ 150 kg/ha has shown the best treatment combination for the storage of potato at ambient room temperature under semiarid conditions of Hisar (Haryana)
Pressure Shifts in High-Precision Hydrogen Spectroscopy: II. Impact Approximation and Monte-Carlo Simulations
We investigate collisional shifts of spectral lines involving excited
hydrogenic states, where van der Waals coefficients have recently been shown to
have large numerical values when expressed in atomic units. Particular emphasis
is laid on the recent hydrogen 2S-4P experiment (and an ongoing 2S-6P
experiment) in Garching, but numerical input data are provided for other
transitions (e.g., involving S states), as well. We show that the frequency
shifts can be described, to sufficient accuracy, in the impact approximation.
The pressure related effects were separated into two parts, (i) related to
collisions of atoms inside of the beam, and (ii) related to collisions of the
atoms in the atomic beam with the residual background gas. The latter contains
both atomic as well as molecular hydrogen. The dominant effect of intra-beam
collisions is evaluated by a Monte-Carlo simulation, taking the geometry of the
experimental apparatus into account. While, in the Garching experiment, the
collisional shift is on the order of 10 Hz, and thus negligible, it can
decisively depend on the experimental conditions. We present input data which
can be used in order to describe the effect for other transitions of current
and planned experimental interest.Comment: 26 pages; 2 figures; this is part 2 of a series of two papers; part 1
carries article number 075005, while part 2 carries article number 075006 in
the journal (online journal version has been rectified
Colloidal Jamming at Interfaces: a Route to Fluid-bicontinuous Gels
Colloidal particles or nanoparticles, with equal affinity for two fluids, are
known to adsorb irreversibly to the fluid-fluid interface. We present
large-scale computer simulations of the demixing of a binary solvent containing
such particles. The newly formed interface sequesters the colloidal particles;
as the interface coarsens, the particles are forced into close contact by
interfacial tension. Coarsening is dramatically curtailed, and the jammed
colloidal layer seemingly enters a glassy state, creating a multiply connected,
solid-like film in three dimensions. The resulting gel contains percolating
domains of both fluids, with possible uses as, for example, a microreaction
medium
Superfluid current disruption in a chain of weakly coupled Bose-Einstein Condensates
We report the experimental observation of the disruption of the superfluid
atomic current flowing through an array of weakly linked Bose-Einstein
condensates. The condensates are trapped in an optical lattice superimposed on
a harmonic magnetic potential. The dynamical response of the system to a change
of the magnetic potential minimum along the optical lattice axis goes from a
coherent oscillation (superfluid regime) to a localization of the condensates
in the harmonic trap ("classical" insulator regime). The localization occurs
when the initial displacement is larger than a critical value or, equivalently,
when the velocity of the wavepacket's center of mass is larger than a critical
velocity dependent on the tunnelling rate between adjacent sites.Comment: 8 pages, 4 figure
Pressure Shifts in High-Precision Hydrogen Spectroscopy: I. Long-Range Atom-Atom and Atom-Molecule Interactions
We study the theoretical foundations for the pressure shifts in
high-precision atomic beam spectrosopy of hydrogen, with a particular emphasis
on transitions involving higher excited P states. In particular, the long-range
interaction of an excited hydrogen atom in a 4P state with a ground-state and
metastable hydrogen atom is studied, with a full resolution of the hyperfine
structure. It is found that the full inclusion of the 4P_1/2 and 4P_3/2
manifolds becomes necessary in order to obtain reliable theoretical
predictions, because the 1S ground state hyperfine frequency is commensurate
with the 4P fine-structure splitting. An even more complex problem is
encountered in the case of the 4P-2S interaction, where the inclusion of
quasi-degenerate 4S-2P_1/2 state becomes necessary in view of the dipole
couplings induced by the van der Waals Hamiltonian. Matrices of dimension up to
40 have to be treated despite all efforts to reduce the problem to irreducible
submanifolds within the quasi-degenerate basis. We focus on the
phenomenologically important second-order van der Waals shifts, proportional to
1/R^6 where R is the interatomic distance, and obtain results with full
resolution of the hyperfine structure. The magnitude of van der Waals
coefficients for hydrogen atom-atom collisions involving excited P states is
drastically enhanced due to energetic quasi-degeneracy; we find no such
enhancement for atom-molecule collisions involving atomic nP states, even if
the complex molecular spectrum involving ro-vibrational levels requires a
deeper analysis.Comment: 32 pages; 2 figures; this is part 1 of a series of two papers; part 1
carries article number 075005, while part 2 carries article number 075006 in
the journal (online journal version has been rectified). arXiv admin note:
text overlap with arXiv:1711.1003
- …