5,528 research outputs found
Collisionally Induced Atomic Clock Shifts and Correlations
We develop a formalism to incorporate exchange symmetry considerations into
the calculation of collisional frequency shifts and blackbody radiation effects
for atomic clock transitions using a density matrix formalism. The formalism is
developed for both fermionic and bosonic atomic clocks. Results for a finite
temperature Sr () atomic clock in a magic
wavelength optical lattice are presented.Comment: 11 pages, 9 figures. Physical Review A (in press
Power densities for two-step gamma-ray transitions from isomeric states
We have calculated the incident photon power density P_2 for which the
two-step induced emission rate from an isomeric nucleus becomes equal to the
natural isomeric decay rate. We have analyzed two-step transitions for isomeric
nuclei with a half-life greater than 10 min, for which there is an intermediate
state of known energy, spin and half-life, for which the intermediate state is
connected by a known gamma-ray transition to the isomeric state and to at least
another intermediate state, and for which the relative intensities of the
transitions to lower states are known. For the isomeric nucleus 166m-Ho, which
has a 1200 y isomeric state at 5.98 keV, we have found a value of P_2=6.3 x
10^7 W cm^{-2}, the intermediate state being the 263.8 keV level. We have found
power densities P_2 of the order of 10^{10} W cm^{-2} for several other
isomeric nuclei.Comment: 9 pages, 1 eps figure, 1 tabl
Partially incoherent gap solitons in Bose-Einstein condensates
We construct families of incoherent matter-wave solitons in a repulsive
degenerate Bose gas trapped in an optical lattice (OL), i.e., gap solitons, and
investigate their stability at zero and finite temperature, using the
Hartree-Fock-Bogoliubov equations. The gap solitons are composed of a coherent
condensate, and normal and anomalous densities of incoherent vapor co-trapped
with the condensate. Both intragap and intergap solitons are constructed, with
chemical potentials of the components falling in one or different bandgaps in
the OL-induced spectrum. Solitons change gradually with temperature. Families
of intragap solitons are completely stable (both in direct simulations, and in
terms of eigenvalues of perturbation modes), while the intergap family may have
a very small unstable eigenvalue (nevertheless, they feature no instability in
direct simulations). Stable higher-order (multi-humped) solitons, and bound
complexes of fundamental solitons are found too.Comment: 8 pages, 9 figures. Physical Review A, in pres
Interferences in the density of two Bose-Einstein condensates consisting of identical or different atoms
The density of two {\it initially independent} condensates which are allowed
to expand and overlap can show interferences as a function of time due to
interparticle interaction. Two situations are separately discussed and
compared: (1) all atoms are identical and (2) each condensate consists of a
different kind of atoms. Illustrative examples are presented.Comment: 12 pages, 3 figure
Many-body effects on adiabatic passage through Feshbach resonances
We theoretically study the dynamics of an adiabatic sweep through a Feshbach
resonance, thereby converting a degenerate quantum gas of fermionic atoms into
a degenerate quantum gas of bosonic dimers. Our analysis relies on a zero
temperature mean-field theory which accurately accounts for initial molecular
quantum fluctuations, triggering the association process. The structure of the
resulting semiclassical phase space is investigated, highlighting the dynamical
instability of the system towards association, for sufficiently small detuning
from resonance. It is shown that this instability significantly modifies the
finite-rate efficiency of the sweep, transforming the single-pair exponential
Landau-Zener behavior of the remnant fraction of atoms Gamma on sweep rate
alpha, into a power-law dependence as the number of atoms increases. The
obtained nonadiabaticity is determined from the interplay of characteristic
time scales for the motion of adiabatic eigenstates and for fast periodic
motion around them. Critical slowing-down of these precessions near the
instability leads to the power-law dependence. A linear power law is obtained when the initial molecular fraction is smaller than the 1/N
quantum fluctuations, and a cubic-root power law is
attained when it is larger. Our mean-field analysis is confirmed by exact
calculations, using Fock-space expansions. Finally, we fit experimental low
temperature Feshbach sweep data with a power-law dependence. While the
agreement with the experimental data is well within experimental error bars,
similar accuracy can be obtained with an exponential fit, making additional
data highly desirable.Comment: 9 pages, 9 figure
On the reliability of the theoretical internal conversion coefficients
Possible sources of uncertainties in the calculations of the internal
conversion coefficients are studied. The uncertainties induced by them are
estimated.Comment: 16 pages (including 3 figures inserted by 'epsfig' macro
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
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