2,359 research outputs found
Effect of the Zero-Mode on the Response of a Trapped Bose-Condensed Gas
The dynamical response of a trapped Bose-Einstein condensate (BEC) is
formulated consistently with quantum field theory and is numerically evaluated.
We regard the BEC as a manifestation of the breaking of the global phase
symmetry. Then, the Goldstone theorem implies the existence of a zero energy
excitation mode (the zero-mode). We calculate the effect of the zero-mode on
the response frequency and show that the contribution of the zero-mode to the
first excitation mode is not so important in the parameter set realized in the
existing experiment. This is the reason that experimental results can be
described using the Bogoliubov prescription, although it breaks the consistency
of the description in quantum field theory.Comment: 18 pages, 3 figure
Condition for emergence of complex eigenvalues in the Bogoliubov-de Gennes equations
The condition for the appearance of dynamical instability of the
Bose-condensed system, characterized by the emergence of complex eigenvalues in
the Bogoliubov-de Gennes equations, is studied analytically. We perturbatively
expand both the Gross-Pitaevskii and Bogoliubov-de Gennes equations with
respect to the coupling constant. It is concluded that the degeneracy between a
positive-norm eigenmode and a negative-norm one is essential for the emergence
of complex modes. Based on the conclusion, we justify the two-mode
approximation applied in our previous work [E. Fukuyama \textit{et al}., Phys.
Rev. A {\bf 76}, 043608 (2007)], in which we analytically studied the condition
for the existence of complex modes when the condensate has a highly quantized
vortex.Comment: 7page
Quantum Field Theoretical Analysis on Unstable Behavior of Bose-Einstein Condensates in Optical Lattices
We study the dynamics of Bose-Einstein condensates flowing in optical
lattices on the basis of quantum field theory. For such a system, a
Bose-Einstein condensate shows a unstable behavior which is called the
dynamical instability. The unstable system is characterized by the appearance
of modes with complex eigenvalues. Expanding the field operator in terms of
excitation modes including complex ones, we attempt to diagonalize the
unperturbative Hamiltonian and to find its eigenstates. It turns out that
although the unperturbed Hamiltonian is not diagonalizable in the conventional
bosonic representation the appropriate choice of physical states leads to a
consistent formulation. Then we analyze the dynamics of the system in the
regime of the linear response theory. Its numerical results are consitent with
as those given by the discrete nonlinear Schrodinger equation.Comment: 16pages, 4figure
Condition for the Existence of Complex Modes in a Trapped Bose--Einstein Condensate with a Highly Quantized Vortex
We consider a trapped Bose--Einstein condensate (BEC) with a highly quantized
vortex. For the BEC with a doubly, triply or quadruply quantized vortex, the
numerical calculations have shown that the Bogoliubov--de Gennes equations,
which describe the fluctuation of the condensate, have complex eigenvalues. In
this paper, we obtain the analytic expression of the condition for the
existence of complex modes, using the method developed by Rossignoli and
Kowalski [R. Rossignoli and A. M. Kowalski, Phys. Rev. A 72, 032101 (2005)] for
the small coupling constant. To derive it, we make the two-mode approximation.
With the derived analytic formula, we can identify the quantum number of the
complex modes for each winding number of the vortex. Our result is consistent
with those obtained by the numerical calculation in the case that the winding
number is two, three or four. We prove that the complex modes always exist when
the condensate has a highly quantized vortex
Gamma Irradiation on Growth and Development of Amorphophallus Muelleri Blume.
Iles-iles (Amorphophallus muelleri Blume) produces apomictic seeds lead to low genetic variation. In order to induce genetic variation, germinated seeds were exposed to Gamma irradiation (Co-60) at doses of 10 to 100 Gy. Seed irradiation was conducted at Center for the Application of Isotope and Irradiation Technology -National Nuclear Energy Agency (CAIRT), Indonesia. Morphology and yield of M1 generation were observed. Results showed that irradiation at a dose of 10 Gy close to LD50 with survival rate 56%. Gamma irradiation at a dose of 10 Gy delayed seeds germination. Germination rates gradually increased and reached maximum at 4 weeks after planting (WAP) for control plants, and 14 WAP of irradiated plants. At 16 WAP, germination rate of 10 Gy irradiated plants was 56% and 84% for those of control plants. Irradiation induced chimera as indicated by short petiole, variegated and abnornal shape of leaflets. Some irradiated plants entered dormancy at 8-10 weeks later than control ones. Prolong vegetative periode lead the plants to produce heavier corms. This study revealed the possibility to induce variation of A. muelleri by using gamma irradition. Keywords: Amorphophallus muelleri, gamma irradiation (Co-60), morphological variation, mutation breedin
Fermi surface in BaNiP
We report measurements of the de Haas-van Alphen (dHvA) oscillation and a
band structure calculation for the pnictide superconductor BaNiP, which
is isostructural to BaFeAs, the mother compound of the iron-pnictide
high- superconductor (BaK)FeAs. Six dHvA-frequency
branches with frequencies up to 8 kT were observed, and they are in
excellent agreement with results of the band-structure calculation. The
determined Fermi surface is large, enclosing about one electron and hole per
formula unit, and three-dimensional. This is in contrast to the small
two-dimensional Fermi surface expected for the iron-pnictide high-
superconductors. The mass enhancement is about two.Comment: To appear in J. Phys. Soc. Jpn., Vol. 78, No.
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