9,419 research outputs found
Matter wave quantum dots (anti-dots) in ultracold atomic Bose-Fermi mixtures
The properties of ultracold atomic Bose-Fermi mixtures in external potentials
are investigated and the existence of gap solitons of Bose-Fermi mixtures in
optical lattices demonstrated. Using a self-consistent approach we compute the
energy spectrum and show that gap solitons can be viewed as matter wave
realizations of quantum dots (anti-dots) with the bosonic density playing the
role of trapping (expulsive) potential for the fermions. The fermionic states
trapped in the condensate are shown to be at the bottom of the Fermi sea and
therefore well protected from thermal decoherence. Energy levels, filling
factors and parameters dependence of gap soliton quantum dots are also
calculated both numerically and analytically.Comment: Extended version of talk given at the SOLIBEC conference, Almagro,
Spain, 8-12 February 2005. To be published on Phys.Rev.
Extraction of and from experimental decay rates using lattice QCD form factors
We present a determination of the Cabibbo-Kobayashi-Maskawa matrix elements
and obtained by combining the momentum dependence of the
semileptonic vector form factors and , recently determined from lattice QCD simulations, with the
differential rates measured for the semileptonic and decays. Our analysis is based on the results for the
semileptonic form factors produced by the European Twisted Mass Collaboration
with flavors of dynamical quarks in the whole range of values
of the squared 4-momentum transfer accessible in the experiments. The
statistical and systematic correlations between the lattice data as well as
those present in the experimental data are properly taken into account. With
respect to the standard procedure based on the use of only the vector form
factor at zero 4-momentum transfer, we obtain more precise and consistent
results: and . The
second-row CKM unitarity is fulfilled within the current uncertainties:
. Moreover, using for the
first time hadronic inputs determined from first principles, we have calculated
the ratio of the semileptonic decay rates into muons and
electrons, which represent a test of lepton universality within the SM,
obtaining in the isospin-symmetric limit of QCD: and .Comment: 8 pages, 2 figures, 8 tables. Version to appear in EPJ
Thermal conductance measurements of pressed OFHC copper contacts at liquid helium temperatures
The thermal conductance of oxygen-free high conductivity (OFHC) copper sample pairs with surface finishes ranging from 0.1 to 1.6-micrometers rms roughness was investigated over the range of 1.6 to 6.0-K under applied contact forces up to 670 N. The thermal conductance increases with increasing contact force; however, no correlation can be drawn with respect to surface finish
Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential
We study the exact dynamics of a one-dimensional spin-polarized gas of
fermions in a double-well potential at zero and finite temperature. Despite the
system is made of non-interacting fermions, its dynamics can be quite complex,
showing strongly aperiodic spatio-temporal patterns during the tunneling. The
extension of these results to the case of mixtures of spin-polarized fermions
in interaction with self-trapped Bose-Einstein condensates (BECs) at zero
temperature is considered as well. In this case we show that the fermionic
dynamics remains qualitatively similar to the one observed in absence of BEC
but with the Rabi frequencies of fermionic excited states explicitly depending
on the number of bosons and on the boson-fermion interaction strength. From
this, the possibility to control quantum fermionic dynamics by means of
Feshbach resonances is suggested.Comment: Accepted for publication in Phys. Rev.
Hypercubic effects in semileptonic decays of heavy mesons, toward , with Twisted fermions
We present a preliminary study toward a lattice determination of the vector
and scalar form factors of the semileptonic decays. We
compute the form factors relative to the transition between heavy-light
pseudoscalar mesons, with masses above the physical D-mass, and the pion. We
simulate heavy-quark masses in the range .
Lorentz symmetry breaking due to hypercubic effects is clearly observed in the
data, and included in the decomposition of the current matrix elements in terms
of additional form factors. We discuss the size of this breaking as the
parent-meson mass increases. Our analysis is based on the gauge configurations
produced by the European Twisted Mass Collaboration with
flavors of dynamical quarks at three different values of the lattice spacing
and with pion masses as small as MeV.Comment: 7 pages, 5 figures; contribution to the XXXVI International Symposium
on Lattice Field Theory (LATTICE2018), East Lansing (Michigan State
University, USA), July 22-28, 201
Mixed symmetry localized modes and breathers in binary mixtures of Bose-Einstein condensates in optical lattices
We study localized modes in binary mixtures of Bose-Einstein condensates
embedded in one-dimensional optical lattices. We report a diversity of
asymmetric modes and investigate their dynamics. We concentrate on the cases
where one of the components is dominant, i.e. has much larger number of atoms
than the other one, and where both components have the numbers of atoms of the
same order but different symmetries. In the first case we propose a method of
systematic obtaining the modes, considering the "small" component as
bifurcating from the continuum spectrum. A generalization of this approach
combined with the use of the symmetry of the coupled Gross-Pitaevskii equations
allows obtaining breather modes, which are also presented.Comment: 11 pages, 16 figure
Thermal conductance of pressed contacts at liquid helium temperatures
The thermal contact conductance of a 0.4 micrometer surface finish OFHC copper sample pair has been investigated from 1.6 to 3.8 K for a range of applied contact forces up to 670 N. Experimental data have been fitted to the relation Q = the integral alpha T to the nth power dt by assuming that the thermal contact conductance is a simple power function of the sample temperature. It has been found that the conductance is proportional to T squared and that conductance increases with an increase in applied contact force. These results confirm earlier work
Performance of all-metal demountable cryogenic seals at superfluid helium temperatures
Two all-metal demountable cryogenic seals with an outside diameter of 36.6 mm, inside diameter of 27.2 mm, and thickness of 0.51 mm were leak-tested at room temperature (300 K), liquid nitrogen temperature (21 cycles at 77 K), liquid helium temperature (9 cycles at 4.2 K), and susperfluid helium temperature (4 cycles at 1.6 K). Each seal was mounted and demounted for 13 cycles. Thickness measurements at 90 deg intervals along the circumference showed a maximum seal compression of 0.038 mm. Leak-rate measurements at all temperatures showed no detectable leak above the helium background level, typically 0.1 x 10(-9) std-cc/sec, during testing
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