Reply to comment ``On the test of the modified BCS at finite temperature''

This is our formal Reply to revised version (v2) of arXiv: nucl-th/0510004v2.Comment: accepted in Physical Review

Quantum Size Effect in Conductivity of Multilayer Metal Films

Conductivity of quantized multilayer metal films is analyzed with an emphasis on scattering by rough interlayer interfaces. Three different types of quantum size effect (QSE) in conductivity are predicted. Two of these QSE are similar to those in films with scattering by rough walls. The third type of QSE is unique and is observed only for certain positions of the interface. The corresponding peaks in conductivity are very narrow and high with a finite cutoff which is due only to some other scattering mechanism or the smearing of the interface. There are two classes of these geometric resonances. Some of the resonance positions of the interface are universal and do not depend on the strength of the interface potential while the others are sensitive to this potential. This geometric QSE gradually disappears with an increase in the width of the interlayer potential barrier.Comment: 12 pages, 10 figures, RevTeX4, to be published in Phys. Rev B (April 2003

Test of modified BCS model at finite temperature

A recently suggested modified BCS (MBCS) model has been studied at finite temperature. We show that this approach does not allow the existence of the normal (non-superfluid) phase at any finite temperature. Other MBCS predictions such as a negative pairing gap, pairing induced by heating in closed-shell nuclei, and ``superfluid -- super-superfluid'' phase transition are discussed also. The MBCS model is tested by comparing with exact solutions for the picket fence model. Here, severe violation of the internal symmetry of the problem is detected. The MBCS equations are found to be inconsistent. The limit of the MBCS applicability has been determined to be far below the ``superfluid -- normal'' phase transition of the conventional FT-BCS, where the model performs worse than the FT-BCS.Comment: 8 pages, 9 figures, to appear in PR

ac-driven atomic quantum motor

We invent an ac-driven quantum motor consisting of two different, interacting ultracold atoms placed into a ring-shaped optical lattice and submerged in a pulsating magnetic field. While the first atom carries a current, the second one serves as a quantum starter. For fixed zero-momentum initial conditions the asymptotic carrier velocity converges to a unique non-zero value. We also demonstrate that this quantum motor performs work against a constant load.Comment: 4 pages, 4 figure

Two-Dimensional Dynamics of Ultracold Atoms in Optical Lattices

We analyze the dynamics of ultracold atoms in optical lattices induced by a sudden shift of the underlying harmonic trapping potential. In order to study the effect of strong interactions, dimensionality and lattice topology on transport properties, we consider bosonic atoms with arbitrarily strong repulsive interactions, on a two-dimensional square lattice and a hexagonal lattice. On the square lattice we find insulating behavior for weakly interacting atoms and slow relaxation for strong interactions, even when a Mott plateau is present, which in one dimension blocks the dynamics. On the hexagonal lattice the center of mass relaxes to the new equilibrium for any interaction strength.Comment: 4 pages, 6 figures; references added; improved figure

Can We Apply Statistical Laws to Small Systems? the Cerium Atom

It is shown that statistical mechanics is applicable to quantum systems with finite numbers of particles, such as complex atoms, atomic clusters, etc., where the residual two-body interaction is sufficiently strong. This interaction mixes the unperturbed shell-model basis states and produces ``chaotic'' many-body eigenstates. As a result, an interaction-induced equilibrium emerges in the system, and temperature can be introduced. However, the interaction between the particles and their finite number can lead to prominent deviations of the equilibrium occupation numbers distribution from the Fermi-Dirac shape. For example, this takes place in the cerium atom with four valence electrons, which was used to compare the theory with realistic numerical calculations.Comment: 4 pages, Latex, two figures in eps-forma