1,516 research outputs found
A new Bloch period for interacting cold atoms in 1D optical lattices
The paper studies Bloch oscillations of ultracold atoms in optical lattice in
the presence of atom-atom interaction. A new, interaction-induced Bloch period
is identified. The analytical results are corroborated by realistic numerical
calculations.Comment: revtex4, 4 pages, 4 figures, gzipped tar fil
Sensitive measurement of forces at micron scale using Bloch oscillations of ultracold atoms
We show that Bloch oscillations of ultracold fermionic atoms in the periodic
potential of an optical lattice can be used for a sensitive measurement of
forces at the micrometer length scale, e.g. in the vicinity of dielectric
surface. In particular, the proposed approach allows to perform a local and
direct measurement of the Casimir-Polder force which is, for realistic
experimental parameters, as large as 10^-4 gravity
Probing neutrino mass hierarchies and with supernova neutrinos
We investigate the feasibility of probing the neutrino mass hierarchy and the
mixing angle with the neutrino burst from a future supernova. An
inverse power-law density with varying is adopted in the
analysis as the density profile of a typical core-collapse supernova. The
survival probabilities of and are shown to reduce to
two-dimensional functions of and . It is found that in the
parameter space, the 3D plots of the probability
functions exhibit highly non-trivial structures that are sensitive to the mass
hierarchy, the mixing angle , and the value of . The conditions
that lead to observable differences in the 3D plots are established. With the
uncertainty of considered, a qualitative analysis of the Earth matter
effect is also included.Comment: 16 pages, 3 figures. Ref [11] added, and some typos correcte
Atom interferometry with trapped Fermi gases
We realize an interferometer with an atomic Fermi gas trapped in an optical
lattice under the influence of gravity. The single-particle interference
between the eigenstates of the lattice results in macroscopic Bloch
oscillations of the sample. The absence of interactions between fermions allows
a time-resolved study of many periods of the oscillations, leading to a
sensitive determination of the acceleration of gravity. The experiment proves
the superiorness of non interacting fermions with respect to bosons for
precision interferometry, and offers a way for the measurement of forces with
microscopic spatial resolution.Comment: 4 pages, 4 figure
Landau-Zener Tunnelling in Waveguide Arrays
Landau-Zener tunnelling is discussed in connection with optical waveguide
arrays. Light injected in a specific band of the Bloch spectrum in the
propagation constant can be transmitted to another band, changing its physical
properties. This is achieved using two waveguide arrays with different
refractive indices, which amounts to consider a Schr\"odinger equation in a
periodic potential with a step. The step causes wave "acceleration" and thus
induces Landau-Zener tunnelling. The region of physical parameters where this
phenomenon can occur is analytically determined and a realistic experimental
setup is suggested. Its application could allow the realization of light
filters.Comment: 4 pages, 6 figure
Disorder-Induced First Order Transition and Curie Temperature Lowering in Ferromagnatic Manganites
We study the effect that size disorder in the cations surrounding manganese
ions has on the magnetic properties of manganites. This disorder is mimic with
a proper distribution of spatially disordered Manganese energies. Both, the
Curie temperature and the order of the transition are strongly affected by
disorder. For moderate disorder the Curie temperature decreases linearly with
the the variance of the distribution of the manganese site energies, and for a
disorder comparable to that present in real materials the transition becomes
first order. Our results provide a theoretical framework to understand disorder
effects on the magnetic behavior of manganites.Comment: 4 pages, three figures include
Nonlinear adiabatic passage from fermion atoms to boson molecules
We study the dynamics of an adiabatic sweep through a Feshbach resonance in a
quantum gas of fermionic atoms. Analysis of the dynamical equations, supported
by mean-field and many-body numerical results, shows that the dependence of the
remaining atomic fraction on the sweep rate varies from
exponential Landau-Zener behavior for a single pair of particles to a power-law
dependence for large particle number . The power-law is linear, , when the initial molecular fraction is smaller than the 1/N
quantum fluctuations, and when it is larger.
Experimental data agree better with a linear dependence than with an
exponential Landau-Zener fit, indicating that many-body effects are significant
in the atom-molecule conversion process.Comment: 5 pages, 4 figure
Resonant tunneling in a schematic model
Tunneling of an harmonically bound two-body system through an external
Gaussian barrier is studied in a schematic model which allows for a better
understanding of intricate quantum phenomena. The role of finite size and
internal structure is investigated in a consistent treatment. The excitation of
internal degrees of freedom gives rise to a peaked structure in the penetration
factor. The model results indicate that for soft systems the adiabatic limit is
not necessarily reached although often assumed in fusion of nuclei and in
electron screening effects at astrophysical energies.Comment: 7 pages, 7 figure
Berry phase for ferromagnet with fractional spin
We study the double exchange model on two lattice sites with one conduction
electron in the limit of an infinite Hund's interaction. While this simple
problem is exactly solvable, we present an approximate solution which is valid
in the limit of large core spins. This solution is obtained by integrating out
charge degrees of freedom. The effective action of two core spins obtained in
the result of such an integration resembles the action of two fractional spins.
We show that the action obtained via naive gradient expansion is inconsistent.
However, a ``non-perturbative'' treatment leads to an extra term in the
effective action which fixes this inconsistency. The obtained ``Berry phase
term'' is geometric in nature. It arises from a geometric constraint on a
target space imposed by an adiabatic approximation.Comment: 11 pages, 3 figures, revtex
Dynamic Fano Resonance of Quasienergy Excitons in Superlattices
The dynamic Fano resonance (DFR) between discrete quasienergy excitons and
sidebands of their ionization continua is predicted and investigated in dc- and
ac-driven semiconductor superlattices. This DFR, well controlled by the ac
field, delocalizes the excitons and opens an intrinsic decay channel in
nonlinear four-wave mixing signals.Comment: 4pages, 4figure
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