131 research outputs found
Mechanism of Anomalous Tunneling in Condensed Bose System
We clarify the origin of anomalous tunneling [Yu. Kagan et al. Phys. Rev.
Lett. 90 (2003) 130402] i.e. the perfect transmission at low energy limit of
tunneling of phonon excitations across the potential barrier separating two
Bose condensates. The perfect transmission is a consequence of the coincidence
of the wave function of the excited state at low energy limit and the
macroscopic wave function of the condensate. We show that the perfect
transmission at low energy occurs even at finite temperatures within the scheme
of Popov approximation.Comment: 4 pages 1 figur
Comment on ``Nonlinear band structure in Bose-Einstein condensates: Nonlinear Sch\"odinger equation with a Kronig Penney potential"
In their recent paper [Phys. Rev. A 71, 033622], B. T. Seaman et al. studied
Bloch states of the condensate wave function in a Kronig-Penney potential and
calculated the band structure. They argued that the effective mass is always
positive when a swallow-tail energy loop is present in the band structure. In
this comment, we reexamine their argument by actually calculating the effective
mass. It is found that there exists a region where the effective mass is
negative even when a swallow-tail is present. Based on this fact, we discuss
the interpretation of swallow-tails in terms of superfluidity.Comment: 3 pages, 3 figure
Response of the Higgs amplitude mode of superfluid Bose gases in a three dimensional optical lattice
We study the Higgs mode of superfluid Bose gases in a three dimensional
optical lattice, which emerges near the quantum phase transition to the Mott
insulator at commensurate fillings. Specifically, we consider responses of the
Higgs mode to temporal modulations of the onsite interaction and the hopping
energy. In order to calculate the response functions including the effects of
quantum and thermal fluctuations, we map the Bose-Hubbard model onto an
effective pseudospin-one model and use a perturbative expansion based on the
imaginary-time Green's function theory. We also include the effects of an
inhomogeneous trapping potential by means of a local density approximation. We
find that the response function for the hopping modulation is equal to that for
the interaction modulation within our approximation. At the unit filling rate
and in the absence of a trapping potential, we show that the Higgs mode can
exist as a sharp resonance peak in the dynamical susceptibilities at typical
temperatures. However, the resonance peak is significantly broadened due to the
trapping potential when the modulations are applied globally to the entire
system. We suggest that the Higgs mode can be detected as a sharp resonance
peak by partial modulations around the trap center.Comment: 22 pages, 9 figure
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