155 research outputs found
Calculation of the even-odd energy difference in superfluid Fermi systems using the pseudopotential theory
The pseudopotential theory is extended to the Bogoliubov-de Gennes equations
to determine the excess energy when one atom is added to the trapped superfluid
Fermi system with even number of atoms. Particular attention is paid to systems
being at the Feshbach resonance point. The results for relatively small
particle numbers are in harmony with the Monte-Carlo calculations, but are also
relevant for systems with larger particle numbers. Concerning the additional
one quasiparticle state we define and determine two new universal numbers to
characterize its widths.Comment: Revised manuscript, results unchanged, 5 pages 4 figure
Transition from Poissonian to GOE level statistics in a modified Artin's billiard
One wall of Artin's billiard on the Poincar\'e half plane is replaced by a
one-parameter () family of nongeodetic walls. A brief description of the
classical phase space of this system is given. In the quantum domain, the
continuousand gradual transition from the Poisson like to GOE level statistics
due to the small perturbations breaking the symmetry responsible for the
'arithmetic chaos' at is studied. Another GOE \rightrrow Poisson
transition due to the mixed phase space for large perturbations is also
investigated. A satisfactory description of the intermediate level statistics
by the Brody distribution was found in boh cases. The study supports the
existence of a scaling region around . A finite size scaling relation
for the Brody-parameter as a function of and the number of levels
considered can be established
Analytical evaluation of the coefficients of the Hu-Paz-Zhang master equation: Ohmic spectral density, zero temperature, and consistency check
We investigate the exact master equation of Hu, Paz, and Zhang for a quantum
harmonic oscillator at zero temperature with a Lorentz-Drude type Ohmic
spectral density. This master equation plays an important role in the study of
quantum Brownian motion and in various applications. In this paper, we give an
analytical evaluation of the coefficients of this non-Markovian master equation
without Lindblad form, which allows us to investigate consistencies of the
solutions, the positivity of the stationary density operator, and the
boundaries of the model's parameters.Comment: 17 pages, 8 figure
Semiclassical Solution of the Quantum Hydrodynamic Equation for Trapped Bose-condensed Gas in the l=0 Case
In this paper the quantum hydrodynamic equation describing the collective,
low energy excitations of a dilute atomic Bose gas in a given trapping
potential is investigated with the JWKB semiclassical method. In the case of
spherically symmetric harmonic confining potential a good agreement is shown
between the semiclassical and the exact energy eigenvalues as well as wave
functions. It is also demonstrated that for larger quantum numbers the
calculation of the semiclassical wave function is numerically more stable than
the exact polynomial with large alternating coefficients.Comment: 12 pages, 7 figure
Semiclassical wave functions and energy levels of Bose-condensed gases in spherically symmetric traps
The WKB-approximation for the Bogoliubov-equations of the quasi-particle
excitations in Bose-gases with condensate is worked out in the case of
spherically symmetric trap potentials on the basis of the resulting
quantization rule. The excitation spectrum is calculated numerically and also
analytically in certain limiting cases. It is found that the energy levels of a
Bohr-Sommerfeld type quantization may be considerably shifted when the
classical turning point gets close to the surface of the condensate.Comment: 4 pages Latex, 1 ps-fil
Range of applicability of the Hu-Paz-Zhang master equation
We investigate a case of the Hu-Paz-Zhang master equation of the
Caldeira-Leggett model without Lindblad form obtained in the weak-coupling
limit up to the second-order perturbation. In our study, we use Gaussian
initial states to be able to employ a sufficient and necessary condition, which
can expose positivity violations of the density operator during the time
evolution. We demonstrate that the evolution of the non-Markovian master
equation has problems when the stationary solution is not a positive operator,
i.e., does not have physical interpretation. We also show that solutions always
remain physical for small-times of evolution. Moreover, we identify a strong
anomalous behavior, when the trace of the solution is diverging. We also
provide results for the corresponding Markovian master equation and show that
positivity violations occur for various types of initial conditions even when
the stationary solution is a positive operator. Based on our numerical results,
we conclude that this non-Markovian master equation is superior to the
corresponding Markovian one.Comment: 14 pages, 19 figure
MICU1 Interacts with the D-Ring of the MCU Pore to Control Its Ca2+ Flux and Sensitivity to Ru360
Proper control of the mitochondrial Ca2+ uniporter's pore (MCU) is required to allow Ca2+-dependent activation of oxidative metabolism and to avoid mitochondrial Ca2+ overload and cell death. The MCU's gatekeeping and cooperative activation is mediated by the Ca2+-sensing MICU1 protein, which has been proposed to form dimeric complexes anchored to the EMRE scaffold of MCU. We unexpectedly find that MICU1 suppresses inhibition of MCU by ruthenium red/Ru360, which bind to MCU's DIME motif, the selectivity filter. This led us to recognize in MICU1's sequence a putative DIME interacting domain (DID), which is required for both gatekeeping and cooperative activation of MCU and for cell survival. Thus, we propose that MICU1 has to interact with the D-ring formed by the DIME domains in MCU to control the uniporter. Copyright © 2018 Elsevier Inc. All rights reserved
Finite temperature hydrodynamic modes of trapped quantum gases
The hydrodynamic equations of an ideal fluid formed by a dilute quantum gas
in a parabolic trapping potential are studied analytically and numerically. Due
to the appearance of internal modes in the fluid stratified by the trapping
potential, the spectrum of low-lying modes is found to be dense in the
high-temperature limit, with an infinitely degenerate set of zero-frequency
modes. The spectrum for Bose-fluids and Fermi-fluids is obtained and discussed.Comment: 26 pages, Late
Newton's identities and positivity of trace class integral operators
We provide a countable set of conditions based on elementary symmetric
polynomials that are necessary and sufficient for a trace class integral
operator to be positive semidefinite, which is an important cornerstone for
quantum theory in phase-space representation. We also present a new,
efficiently computable algorithm based on Newton's identities. Our test of
positivity is much more sensitive than the ones given by the linear entropy and
Robertson-Schr\"odinger's uncertainty relations; our first condition is
equivalent to the non-negativity of the linear entropy.Comment: 15 pages, 6 figure
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