2,153 research outputs found
Effective-range approach and scaling laws for electromagnetic strength in neutron-halo nuclei
We study low-lying multipole strength in neutron-halo nuclei. The strength
depends only on a few low-energy constants: the neutron separation energy, the
asymptotic normalization coefficient of the bound state wave function, and the
scattering length that contains the information on the interaction in the
continuum. The shape of the transition probability shows a characteristic
dependence on few scaling parameters and the angular momenta. The total E1
strength is related to the root-mean-square radius of the neutron wave function
in the ground state and shows corresponding scaling properties. We apply our
approach to the E1 strength distribution of 11Be.Comment: 4 pages, 1 figure (modified), additional table, extended discussion
of example, accepted for publication in Phys. Rev. Let
Spin-based quantum gating with semiconductor quantum dots by bichromatic radiation method
A potential scheme is proposed for realizing a two-qubit quantum gate in
semiconductor quantum dots. Information is encoded in the spin degrees of
freedom of one excess conduction electron of each quantum dot. We propose to
use two lasers, radiation two neighboring QDs, and tuned to blue detuning with
respect to the resonant frequencies of individual excitons. The two-qubit phase
gate can be achieved by means of both Pauli-blocking effect and dipole-dipole
coupling between intermediate excitonic states.Comment: Europhysics Letters 66 (2004) 1
Interferometric thermometry of a single sub-Doppler cooled atom
Efficient self-interference of single-photons emitted by a sideband-cooled
Barium ion is demonstrated. First, the technical tools for performing efficient
coupling to the quadrupolar transition of a single Ba ion are
presented. We show efficient Rabi oscillations of the internal state of the ion
using a highly stabilized 1.76 fiber laser resonant with the
S-D transition. We then show sideband cooling of the ion's
motional modes and use it as a means to enhance the interference contrast of
the ion with its mirror-image to up to 90%. Last, we measure the dependence of
the self-interference contrast on the mean phonon number, thereby demonstrating
the potential of the set-up for single-atom thermometry close to the motional
ground state.Comment: 6 pages, 6 figure
Conductance peaks in open quantum dots
We present a simple measure of the conductance fluctuations in open ballistic
chaotic quantum dots, extending the number of maxima method originally proposed
for the statistical analysis of compound nuclear reactions. The average number
of extreme points (maxima and minima) in the dimensionless conductance, , as
a function of an arbitrary external parameter , is directly related to the
autocorrelation function of . The parameter can be associated to an
applied gate voltage causing shape deformation in quantum dot, an external
magnetic field, the Fermi energy, etc.. The average density of maxima is found
to be , where is a universal constant
and is the conductance autocorrelation length, which is system specific.
The analysis of does not require large statistic samples,
providing a quite amenable way to access information about parametric
correlations, such as .Comment: 5 pages, 5 figures, accepted to be published - Physical Review
Letter
Systematic study of Optical Feshbach Resonances in an ideal gas
Using a narrow intercombination line in alkaline earth atoms to mitigate
large inelastic losses, we explore the Optical Feshbach Resonance (OFR) effect
in an ultracold gas of bosonic Sr. A systematic measurement of three
resonances allows precise determinations of the OFR strength and scaling law,
in agreement with coupled-channels theory. Resonant enhancement of the complex
scattering length leads to thermalization mediated by elastic and inelastic
collisions in an otherwise ideal gas. OFR could be used to control atomic
interactions with high spatial and temporal resolution.Comment: Significant changes to text and figure presentation to improve
clarity. Extended supplementary material. 4 pages, 4 figures; includes
supplementary material 8 pages, 4 figures. Submitted to Physical Review
Letter
Spatial separation in a thermal mixture of ultracold Yb and Rb atoms
We report on the observation of unusually strong interactions in a thermal
mixture of ultracold atoms which cause a significant modification of the
spatial distribution. A mixture of Rb and Yb with a temperature
of a few K is prepared in a hybrid trap consisting of a bichromatic
optical potential superimposed on a magnetic trap. For suitable trap parameters
and temperatures, a spatial separation of the two species is observed. We infer
that the separation is driven by a large interaction strength between
Yb and Rb accompanied by a large three-body recombination rate.
Based on this assumption we have developed a diffusion model which reproduces
our observations
Minimal H\"older regularity implying finiteness of integral Menger curvature
We study two families of integral functionals indexed by a real number . One family is defined for 1-dimensional curves in and the other one
is defined for -dimensional manifolds in . These functionals are
described as integrals of appropriate integrands (strongly related to the
Menger curvature) raised to power . Given we prove that
regularity of the set (a curve or a manifold), with implies finiteness of both curvature functionals
( in the case of curves). We also show that is optimal by
constructing examples of functions with graphs of infinite
integral curvature
Thermal and electrical transport in the spin density wave antiferromagnet CaFeAs
We present here measurements of the thermopower, thermal conductivity, and
electrical resistivity of the newly reported compound CaFe4As3. Evidence is
presented from specific heat and electrical resistivity measurements that a
substantial fraction of the Fermi surface survives the onset of spin density
wave (SDW) order at the Neel temperature TN=88 K, and its subsequent
commensurate lockin transition at T2=26.4 K. The specific heat below T2
consists of a normal metallic component from the ungapped parts of the Fermi
surface, and a Bardeen-Cooper- Schrieffer (BCS) component that represents the
SDW gapping of the Fermi surface. A large Kadowaki-Woods ratio is found at low
temperatures, showing that the ground state of CaFe4As3 is a strongly
interacting Fermi liquid. The thermal conductivity of CaFe4As3 is an order of
magnitude smaller than those of conventional metals at all temperatures, due to
a strong phonon scattering. The thermoelectric power displays a sign change
from positive to negative indicating that a partial gap forms at the Fermi
level with the onset of commensurate spin density wave order at T2=26.4 K. The
small value of the thermopower and the enhancements of the resistivity due to
gap formation and strong quasiparticle interactions offset the low value of the
thermal conductivity, yielding only a modest value for the thermoelectric
figure of merit Z < 5x10^-6 1/K in CaFe4As3. The results of ab initio
electronic structure calculations are reported, confirming that the sign change
in the thermopower at T2 is reflected by a sign change in the slope of the
density of states at the Fermi level. Values for the quasiparticle
renormalization are derived from measurements of the specific heat and
thermopower, indicating that as T->0, CaFe4As3 is among the most strongly
correlated of the known Fe-based pnictide and chalcogenide systems.Comment: 8 pages with 5 figure
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