4,417 research outputs found
Single-particle excitations and the order parameter for a trapped superfluid Fermi gas
We reveal a strong influence of a superfluid phase transition on the
character of single-particle excitations of a trapped neutral-atom Fermi gas.
Below the transition temperature the presence of a spatially inhomogeneous
order parameter (gap) shifts up the excitation eigenenergies and leads to the
appearance of in-gap excitations localized in the outer part of the gas sample.
The eigenenergies become sensitive to the gas temperature and are no longer
multiples of the trap frequencies. These features should manifest themselves in
a strong change of the density oscillations induced by modulations of the trap
frequencies and can be used for identifying the superfluid phase transition.Comment: 5 pages, RevTeX, 2 eps figure
Intrinsic defects in silicon carbide LED as a perspective room temperature single photon source in near infrared
Generation of single photons has been demonstrated in several systems.
However, none of them satisfies all the conditions, e.g. room temperature
functionality, telecom wavelength operation, high efficiency, as required for
practical applications. Here, we report the fabrication of light emitting
diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate
our devices we used a standard semiconductor manufacturing technology in
combination with high-energy electron irradiation. The room temperature
electroluminescence (EL) of our LEDs reveals two strong emission bands in
visible and near infrared (NIR), associated with two different intrinsic
defects. As these defects can potentially be generated at a low or even single
defect level, our approach can be used to realize electrically driven single
photon source for quantum telecommunication and information processing
The bifurcation phenomena in the resistive state of the narrow superconducting channels
We have investigated the properties of the resistive state of the narrow
superconducting channel of the length L/\xi=10.88 on the basis of the
time-dependent Ginzburg-Landau model. We have demonstrated that the bifurcation
points of the time-dependent Ginzburg-Landau equations cause a number of
singularities of the current-voltage characteristic of the channel. We have
analytically estimated the averaged voltage and the period of the oscillating
solution for the relatively small currents. We have also found the range of
currents where the system possesses the chaotic behavior
Polarizations of J/\psi and \psi' in hadroproduction at Tevatron in the k_t factorization approach
We present a calculation for the polarizations of and
produced in the hadron collisions at the Fermilab Tevatron. Various color octet
channels including , , and as
well as contributions from decays are considered in the
factorization approach. We find that in a rather wide range of the transverse
momenta of and , the production rates could be dominated by the
channel, and the predicted polarizations from the
channel and feeddown contributions are roughly
compatible with the preliminary CDF data. This might provide a possible release
from the conflict between the NRQCD collinear parton model calculations and the
CDF data.Comment: 12 pages, 4 PS files, final version for publicatio
Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide
Quantum systems can provide outstanding performance in various sensing
applications, ranging from bioscience to nanotechnology. Atomic-scale defects
in silicon carbide are very attractive in this respect because of the
technological advantages of this material and favorable optical and radio
frequency spectral ranges to control these defects. We identified several,
separately addressable spin-3/2 centers in the same silicon carbide crystal,
which are immune to nonaxial strain fluctuations. Some of them are
characterized by nearly temperature independent axial crystal fields, making
these centers very attractive for vector magnetometry. Contrarily, the
zero-field splitting of another center exhibits a giant thermal shift of -1.1
MHz/K at room temperature, which can be used for thermometry applications. We
also discuss a synchronized composite clock exploiting spin centers with
different thermal response.Comment: 8 pages, 7 figure
BCS pairing in a trapped dipolar Fermi gase
We present a detailed study of the BCS pairing transition in a trapped
polarized dipolar Fermi gas. In the case of a shallow nearly spherical trap, we
find the decrease of the transition temperature as a function of the trap
aspect ratio and predict the existence of the optimal trap geometry. The latter
corresponds to the highest critical temperature of the BCS transition for a
given number of particles. We also derive the phase diagram for an ultracold
trapped dipolar Fermi gases in the situation, where the trap frequencies can be
of the order of the critical temperature of the BCS transition in the
homogeneous case, and find the critical value of the dipole-dipole interaction
energy, below which the BCS transition ceases to exist. The critical dipole
strength is obtained as a function of the trap aspect ratio. Alternatively, for
a given dipole strength there is a critical value of the trap anisotropy for
the BCS state to appear. The order parameter calculated at criticality,
exhibits nover non-monotonic behavior resulted from the combined effect of the
confining potential and anisotropic character of the interparticle
dipole-dipole interation.Comment: 14 pages, 3 figure
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