217 research outputs found
Пропозиції щодо підвищення рівня освіти і збереження культури в рамках комплексної державної програми підтримки ромів України
We consider imbalanced Fermi gases with strong attractive interactions, for which Cooper-pair formation plays an important role. The two-component mixtures consist either of identical fermionic atoms in two different hyperfine states, or of two different atomic species both occupying only a single hyperfine state. In both cases, the number of atoms for each component is allowed to be different, which leads to a spin imbalance, or spin polarization. Two different atomic species also lead to a mass imbalance. Imbalanced Fermi gases are relevant to condensed-matter physics, nuclear physics and astroparticle physics. They have been studied intensively in recent years, following their experimental realization in ultracold atomic Fermi gases. The experimental control in such a system allows for a systematic study of the equation of state and the phase diagram as a function of temperature, spin polarization and interaction strength. In this review, we discuss the progress in understanding strongly-interacting imbalanced Fermi gases, where the main goal is to describe the results of the highly controlled experiments. We start by discussing Feshbach resonances, after which we treat the imbalanced Fermi gas in mean-field theory to give an introduction to the relevant physics. We encounter several unusual superfluid phases, including phase-separation, gapless Sarma superfluidity, and supersolidity. To obtain a more quantitative description of the experiments, we review also more sophisticated techniques, such as diagrammatic methods and the renormalization-group theory. We end the review by discussing two theoretical approaches to treat the inhomogeneous imbalanced Fermi gas, namely the Landau–Ginzburg theory and the Bogoliubov–de Gennes approach
Правова система Італії, структурні елементи кримінального права щодо неповнолітніх в Україні та Італії
Статья посвящена рассмотрению правовой системы Италии, а также
структурных элементов уголовного права. Автор предлагает использовать
положительный опыт Италии для разработки и внедрения изменений и
дополнений к Уголовному Кодексу Украины и отмечает, что «ресоциализация»
преступника занимает особое место в практике итальянского уголовного
права.The article is devoted to the consideration of legal system of Italy and its structural elements of criminal law of minors. The author suggests to use the positive experience of Italy for the development and implementation separate supplements to the Criminal law of Ukraine and underlines the importance of the process of "resocialisation" of young offender
Inelastic light scattering from a Mott insulator
We propose to use Bragg spectroscopy to measure the excitation spectrum of
the Mott insulator state of an atomic Bose gas in an optical lattice. We
calculate the structure factor of the Mott insulator taking into account both
the selfenergy corrections of the atoms and the corresponding dressing of the
atom-photon interaction. We determine the scattering rate of photons in the
stimulated Raman transition and show that by measuring this scattering rate in
an experiment, in particular the excitation gap of the Mott insulator can be
determined.Comment: 4 pages, 7 figures, LaTeX, submitted to PR
Out-of-equilibrium quantum fields with conserved charge
We study the out-of-equilibrium evolution of an O(2)-invariant scalar field
in which a conserved charge is stored. We apply a loop expansion of the
2-particle irreducible effective action to 3-loop order. Equations of motion
are derived which conserve both total charge and total energy yet allow for the
effects of scattering whereby charge and energy can transfer between modes.
Working in (1+1)-dimensions we solve the equations of motion numerically for a
system knocked out of equilibrium by a sudden temperature quench. We examine
the initial stages of the charge and energy redistribution. This provides a
basis from which we can understand the formation of Bose-Einstein condensates
from first principles.Comment: 11 pages, 5 figures, replacement with improved presentatio
Variational self-consistent theory for trapped Bose gases at finite temperature
We apply the time-dependent variational principle of Balian-V\'en\'eroni to a
system of self-interacting trapped bosons at finite temperature. The method
leads to a set of coupled non-linear time dependent equations for the
condensate density, the thermal cloud and the anomalous density. We solve
numerically these equations in the static case for a harmonic trap. We analyze
the various densities as functions of the radial distance and the temperature.
We find an overall good qualitative agreement with recent experiments as well
as with the results of many theoretical groups. We also discuss the behavior of
the anomalous density at low temperatures owing to its importance to account
for many-body effects.Comment: 8 pages, 8 figure
Stability of Bose condensed atomic Li-7
We study the stability of a Bose condensate of atomic Li in a (harmonic
oscillator) magnetic trap at non-zero temperatures. In analogy to the stability
criterion for a neutron star, we conjecture that the gas becomes unstable if
the free energy as a function of the central density of the cloud has a local
extremum which conserves the number of particles. Moreover, we show that the
number of condensate particles at the point of instability decreases with
increasing temperature, and that for the temperature interval considered, the
normal part of the gas is stable against density fluctuations at this point.Comment: Submitted for publication in Physical Review
Quantum Kinetic Theory V: Quantum kinetic master equation for mutual interaction of condensate and noncondensate
A detailed quantum kinetic master equation is developed which couples the
kinetics of a trapped condensate to the vapor of non-condensed particles. This
generalizes previous work which treated the vapor as being undepleted.Comment: RevTeX, 26 pages and 5 eps figure
Cooper pairing and single particle properties of trapped Fermi gases
We calculate the elementary excitations and pairing of a trapped atomic Fermi
gas in the superfluid phase. The level spectra and pairing gaps undergo several
transitions as the strength of the interactions between and the number of atoms
are varied. For weak interactions, the Cooper pairs are formed between
particles residing in the same harmonic oscillator shell. In this regime, the
nature of the paired state is shown to depend critically on the position of the
chemical potential relative to the harmonic oscillator shells and on the size
of the mean field. For stronger interactions, we find a region where pairing
occur between time-reversed harmonic oscillator states in different shells
also.Comment: Slightly revised version: Mistakes in equation references in figures
corrected. Accepted for Phys. Rev.
Atomic Bose Gas with Negative Scattering Length
We derive the equation of state of a dilute atomic Bose gas with an
interatomic interaction that has a negative scattering length and argue that
two continuous phase transitions, occuring in the gas due to quantum degeneracy
effects, are preempted by a first-order gas-liquid or gas-solid transition
depending on the details of the interaction potential. We also discuss the
consequences of this result for future experiments with magnetically trapped
spin-polarized atomic gasses such as lithium and cesium.Comment: 16 PAGES, REVTEX 3.0, ACCEPTED FOR PUBLICATION IN PHYS. REV.
Pairing of fermions in atomic traps and nuclei
Pairing gaps for fermionic atoms in harmonic oscillator traps are calculated
for a wide range of interaction strengths and particle number, and compared to
pairing in nuclei. Especially systems, where the pairing gap exceeds the level
spacing but is smaller than the shell splitting , are studied
which applies to most trapped Fermi atomic systems as well as to finite nuclei.
When solving the gap equation for a large trap with such multi-level pairing,
one finds that the matrix elements between nearby harmonic oscillator levels
and the quasi-particle energies lead to a double logarithm of the gap, and a
pronounced shell structure at magic numbers. It is argued that neutron and
proton pairing in nuclei belongs to the class of multi-level pairing, that
their shell structure follows naturally and that the gaps scale as - all in qualitative agreement with odd-even staggering of nuclear
binding energies. Pairing in large systems are related to that in the bulk
limit. For large nuclei the neutron and proton superfluid gaps approach the
asymptotic value in infinite nuclear matter: MeV.Comment: 11 pages, 5 figure
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