491 research outputs found
Quantum fluctuations and stability of tetrahedral deformations in atomic nuclei
The possible existence of stable axial octupole and tetrahedral deformations
is investigated in Zr and Zr. HFBCS calculations with parity
projection have been performed for various parametrizations of the Skyrme
energy functional. The correlation and excitation energies of negative parity
states associated with shape fluctuations have been obtained using the
generator coordinate method (GCM). The results indicate that in these nuclei
both the axial octupole and tetrahedral deformations are of dynamic character
and possess similar characteristics. Various Skyrme forces give consistent
results as a function of these two octupole degrees of freedom both at the
mean-field level as well as for configuration mixing calculations.Comment: 8 pages, 4 figures, submitted to IJMP
Interleaving Command Sequences: a Threat to Secure Smartcard Interoperability
The increasingly widespread use of smartcards for a variety of sensitive
applications, including digital signatures, creates the need to ensure and
possibly certify the secure interoperability of these devices. Standard
certification criteria, in particular the Common Criteria, define security
requirements but do not sufficiently address the problem of interoperability.
Here we consider the interoperability problem which arises when various
applications interact with different smartcards through a middleware. In such a
situation it is possible that a smartcard of type S receives commands that were
supposed to be executed on a different smartcard of type S'. Such "external
commands" can interleave with the commands that were supposed to be executed on
S. We experimentally demonstrate this problem with a Common Criteria certified
digital signature process on a commercially available smartcard. Importantly,
in some of these cases the digital signature processes terminate without
generating an error message or warning to the user.Comment: 6 pages; published in the 10th WSEAS International Conference on
Information Security and Privacy (ISP 2011
Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture
Radio-frequency spectroscopy is used to study pairing in the normal and
superfluid phases of a strongly interacting Fermi gas with imbalanced spin
populations. At high spin imbalances the system does not become superfluid even
at zero temperature. In this normal phase full pairing of the minority atoms is
observed. This demonstrates that mismatched Fermi surfaces do not prevent
pairing but can quench the superfluid state, thus realizing a system of fermion
pairs that do not condense even at the lowest temperature
Tomographic RF Spectroscopy of a Trapped Fermi Gas at Unitarity
We present spatially resolved radio-frequency spectroscopy of a trapped Fermi
gas with resonant interactions and observe a spectral gap at low temperatures.
The spatial distribution of the spectral response of the trapped gas is
obtained using in situ phase-contrast imaging and 3D image reconstruction. At
the lowest temperature, the homogeneous rf spectrum shows an asymmetric
excitation line shape with a peak at 0.48(4) with respect to the
free atomic line, where is the local Fermi energy
Observation of Feshbach resonances between two different atomic species
We have observed three Feshbach resonances in collisions between lithium-6
and sodium-23 atoms. The resonances were identified as narrow loss features
when the magnetic field was varied. The molecular states causing these
resonances have been identified, and additional lithium-sodium resonances are
predicted. These resonances will allow the study of degenerate Bose-Fermi
mixtures with adjustable interactions, and could be used to generate ultracold
heteronuclear molecules
Formation Time of a Fermion Pair Condensate
The formation time of a condensate of fermionic atom pairs close to a
Feshbach resonance was studied. This was done using a phase-shift method in
which the delayed response of the many-body system to a modulation of the
interaction strength was recorded. The observable was the fraction of condensed
molecules in the cloud after a rapid magnetic field ramp across the Feshbach
resonance. The measured response time was slow compared to the rapid ramp,
which provides final proof that the molecular condensates reflect the presence
of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure
Observation of Bose-Einstein Condensation of Molecules
We have observed Bose-Einstein condensation of molecules. When a spin mixture
of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near
a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below
600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by
the sudden onset of a bimodal density distribution. This condensate realizes
the limit of tightly bound fermion pairs in the crossover between BCS
superfluidity and Bose-Einstein condensation.Comment: 4 pages, 3 figure
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