132 research outputs found
Attosecond two-photon interferometry for doubly excited states of helium
We show that the correlation dynamics in coherently excited doubly excited
resonances of helium can be followed in real time by two-photon interferometry.
This approach promises to map the evolution of the two-electron wave packet
onto experimentally easily accessible non-coincident single electron spectra.
We analyze the interferometric signal in terms of a semi-analytical model which
is validated by a numerical solution of the time-dependent two-electron
Schr\"odinger equation in its full dimensionality.Comment: 5 pages, 4 figure
Observation of Heteronuclear Feshbach Resonances in a Bose-Fermi Mixture
Three magnetic-field induced heteronuclear Feshbach resonances were
identified in collisions between bosonic 87Rb and fermionic 40K atoms in their
absolute ground states. Strong inelastic loss from an optically trapped mixture
was observed at the resonance positions of 492, 512, and 543 +/- 2 G. The
magnetic-field locations of these resonances place a tight constraint on the
triplet and singlet cross-species scattering lengths, yielding -281 +/- 15 Bohr
and -54 +/- 12 Bohr, respectively. The width of the loss feature at 543 G is
3.7 +/- 1.5 G wide; this broad Feshbach resonance should enable experimental
control of the interspecies interactions.Comment: revtex4 + 5 EPS figure
Numerical method for evolving the dipolar projected Gross-Pitaevskii equation
We describe a method for evolving the projected Gross-Pitaevskii equation
(PGPE) for an interacting Bose gas in a harmonic oscillator potential, with the
inclusion of a long-range dipolar interaction. The central difficulty in
solving this equation is the requirement that the field is restricted to a
small set of prescribed modes that constitute the low energy c-field region of
the system. We present a scheme, using a Hermite-polynomial based spectral
representation, that precisely implements this mode restriction and allows an
efficient and accurate solution of the dipolar PGPE. We introduce a set of
auxiliary oscillator states to perform a Fourier transform necessary to
evaluate the dipolar interaction in reciprocal space. We extensively
characterize the accuracy of our approach, and derive Ehrenfest equations for
the evolution of the angular momentum.Comment: 16 pages, 6 figures. Updated to published versio
Resonance phenomena in ultracold dipole-dipole scattering
Elastic scattering resonances occurring in ultracold collisions of either
bosonic or fermionic polar molecules are investigated. The Born-Oppenheimer
adiabatic representation of the two-bodydynamics provides both a qualitative
classification scheme and a quantitative WKB quantization condition that
predicts several sequences of resonant states. It is found that the
near-threshold energy dependence of ultracold collision cross sections varies
significantly with the particle exchange symmetry, with bosonic systems showing
much smoother energy variations than their fermionic counterparts. Resonant
variations of the angular distributions in ultracold collisions are also
described.Comment: 19 pages, 6 figures, revtex4, submitted to J. Phys.
Ultracold polar molecules near quantum degeneracy
We report the creation and characterization of a near quantum-degenerate gas
of polar K-Rb molecules in their absolute rovibrational ground
state. Starting from weakly bound heteronuclear KRb Feshbach molecules, we
implement precise control of the molecular electronic, vibrational, and
rotational degrees of freedom with phase-coherent laser fields. In particular,
we coherently transfer these weakly bound molecules across a 125 THz frequency
gap in a single step into the absolute rovibrational ground state of the
electronic ground potential. Phase coherence between lasers involved in the
transfer process is ensured by referencing the lasers to two single components
of a phase-stabilized optical frequency comb. Using these methods, we prepare a
dense gas of polar molecules at a temperature below 400 nK. This
fermionic molecular ensemble is close to quantum degeneracy and can be
characterized by a degeneracy parameter of . We have measured the
molecular polarizability in an optical dipole trap where the trap lifetime
gives clues to interesting ultracold chemical processes. Given the large
measured dipole moment of the KRb molecules of 0.5 Debye, the study of quantum
degenerate molecular gases interacting via strong dipolar interactions is now
within experimental reach
Creation of ultracold molecules from a Fermi gas of atoms
Since the realization of Bose-Einstein condensates (BEC) in atomic gases an
experimental challenge has been the production of molecular gases in the
quantum regime. A promising approach is to create the molecular gas directly
from an ultracold atomic gas; for example, atoms in a BEC have been coupled to
electronic ground-state molecules through photoassociation as well as through a
magnetic-field Feshbach resonance. The availability of atomic Fermi gases
provides the exciting prospect of coupling fermionic atoms to bosonic
molecules, and thus altering the quantum statistics of the system. This
Fermi-Bose coupling is closely related to the pairing mechanism for a novel
fermionic superfluid proposed to occur near a Feshbach resonance. Here we
report the creation and quantitative characterization of exotic, ultracold
K molecules. Starting with a quantum degenerate Fermi gas of atoms
at T < 150 nanoKelvin we scan over a Feshbach resonance to adiabatically create
over a quarter million trapped molecules, which we can convert back to atoms by
reversing the scan. The small binding energy of the molecules is controlled by
detuning from the Feshbach resonance and can be varied over a wide range. We
directly detect these weakly bound molecules through rf photodissociation
spectra that probe the molecular wavefunction and yield binding energies that
are consistent with theory
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