99 research outputs found
Population redistribution in optically trapped polar molecules
We investigate the rovibrational population redistribution of polar molecules
in the electronic ground state induced by spontaneous emission and blackbody
radiation. As a model system we use optically trapped LiCs molecules formed by
photoassociation in an ultracold two-species gas. The population dynamics of
vibrational and rotational states is modeled using an ab-initio electric dipole
moment function and experimental potential energy curves. Comparison with the
evolution of the v"=3 electronic ground state yields good qualitative
agreement. The analysis provides important input to assess applications of
ultracold LiCs molecules in quantum simulation and ultracold chemistry.Comment: 6 pages, 5 figures, EPJD Topical issue on Cold Quantum Matter -
Achievements and Prospect
Imaging electric fields in the vicinity of cryogenic surfaces using Rydberg atoms
The ability to characterize static and time-dependent electric fields in situ
is an important prerequisite for quantum-optics experiments with atoms close to
surfaces. Especially in experiments which aim at coupling Rydberg atoms to the
near field of superconducting circuits, the identification and subsequent
elimination of sources of stray fields is crucial. We present a technique that
allows the determination of stray-electric-field distributions
at distances of less than from (cryogenic) surfaces using
coherent Rydberg-Stark spectroscopy in a pulsed supersonic beam of metastable
helium atoms. We demonstrate the
capabilities of this technique by characterizing the electric stray field
emanating from a structured superconducting surface. Exploiting coherent
population transfer with microwave radiation from a coplanar waveguide, the
same technique allows the characterization of the microwave-field distribution
above the surface.Comment: 6 pages, 4 figure
Formation of ultracold dipolar molecules in the lowest vibrational levels by photoassociation
We recently reported the formation of ultracold LiCs molecules in the
rovibrational ground state X1Sigma+,v''=0,J''=0 [J. Deiglmayr et al., PRL 101,
133004 (2008)]. Here we discuss details of the experimental setup and present a
thorough analysis of the photoassociation step including the photoassociation
line shape. We predict the distribution of produced ground state molecules
using accurate potential nergy curves combined with an ab-initio dipole
transition moment and compare this prediction with experimental ionization
spectra. Additionally we improve the value of the dissociation energy for the
X1Sigma+ state by high resolution spectroscopy of the vibrational ground state.Comment: Submitted to Faraday Discussions 142: Cold and Ultracold Molecules 18
pages, 8 figure
Influence of a Feshbach resonance on the photoassociation of LiCs
We analyse the formation of ultracold 7Li133Cs molecules in the rovibrational
ground state through photoassociation into the B1Pi state, which has recently
been reported [J. Deiglmayr et al., Phys. Rev. Lett. 101, 133004 (2008)].
Absolute rate constants for photoassociation at large detunings from the atomic
asymptote are determined and are found to be surprisingly large. The
photoassociation process is modeled using a full coupled-channel calculation
for the continuum state, taking all relevant hyperfine states into account. The
enhancement of the photoassociation rate is found to be caused by an `echo' of
the triplet component in the singlet component of the scattering wave function
at the inner turning point of the lowest triplet a3Sigma+ potential. This
perturbation can be ascribed to the existence of a broad Feshbach resonance at
low scattering energies. Our results elucidate the important role of couplings
in the scattering wave function for the formation of deeply bound ground state
molecules via photoassociation.Comment: Added Erratum, 20 pages, 9 figure
Measuring the dispersive frequency shift of a rectangular microwave cavity induced by an ensemble of Rydberg atoms
In recent years the interest in studying interactions of Rydberg atoms or
ensembles thereof with optical and microwave frequency fields has steadily
increased, both in the context of basic research and for potential applications
in quantum information processing. We present measurements of the dispersive
interaction between an ensemble of helium atoms in the 37s Rydberg state and a
single resonator mode by extracting the amplitude and phase change of a weak
microwave probe tone transmitted through the cavity. The results are in
quantitative agreement with predictions made on the basis of the dispersive
Tavis-Cummings Hamiltonian. We study this system with the goal of realizing a
hybrid between superconducting circuits and Rydberg atoms. We measure maximal
collective coupling strengths of 1 MHz, corresponding to 3*10^3 Rydberg atoms
coupled to the cavity. As expected, the dispersive shift is found to be
inversely proportional to the atom-cavity detuning and proportional to the
number of Rydberg atoms. This possibility of measuring the number of Rydberg
atoms in a nondestructive manner is relevant for quantitatively evaluating
scattering cross sections in experiments with Rydberg atoms
Resonant enhancement of ultracold photoassociation rate by electric field induced anisotropic interaction
We study the effects of a static electric field on the photoassociation of a
heteronuclear atom-pair into a polar molecule. The interaction of permanent
dipole moment with a static electric field largely affects the ground state
continuum wave function of the atom-pair at short separations where
photoassociation transitions occur according to Franck-Condon principle.
Electric field induced anisotropic interaction between two heteronuclear ground
state atoms leads to scattering resonances at some specific electric fields.
Near such resonances the amplitude of scattering wave function at short
separation increases by several orders of magnitude. As a result,
photoaasociation rate is enhanced by several orders of magnitude near the
resonances. We discuss in detail electric field modified atom-atom scattering
properties and resonances. We calculate photoassociation rate that shows giant
enhancement due to electric field tunable anisotropic resonances. We present
selected results among which particularly important are the excitations of
higher rotational levels in ultracold photoassociation due to electric field
tunable resonances.Comment: 14 pages,9 figure
Efficient production of polar molecular Bose-Einstein condensates via an all-optical R-type atom-molecule adiabatic passage
We propose a scheme of "-type" photoassociative adiabatic passage (PAP) to
create polar molecular condensates from two different species of ultracold
atoms. Due to the presence of a quasi-coherent population trapping state in the
scheme, it is possible to associate atoms into molecules with a
\textit{low-power} photoassociation (PA) laser. One remarkable advantage of our
scheme is that a tunable atom-molecule coupling strength can be achieved by
using a time-dependent PA field, which exhibits larger flexibility than using a
tunable magnetic field. In addition, our results show that the PA intensity
required in the "-type" PAP could be greatly reduced compared to that in a
conventional "-type" one.Comment: 17 pages, 5 figures, to appear in New Journal of Physic
Rabi oscillations between ground and Rydberg states and van der Waals blockade in a mesoscopic frozen Rydberg gas
We present a detailed analysis of our recent observation of synchronous Rabi
oscillations between the electronic ground state and Rydberg states in a
mesoscopic ensemble containing roughly 100 ultracold atoms [M. Reetz-Lamour
\textit{et al.}, submitted, arXiv:0711.4321]. The mesoscopic cloud is selected
out of a sample of laser-cooled Rb atoms by optical pumping. The atoms are
coupled to a Rydberg state with principal quantum number around 30 by a
two-photon scheme employing flat-top laser beams. The influence of residual
spatial intensity fluctuations as well as sources of decoherence such as
redistribution to other states, radiative lifetime, and laser bandwidth are
analysed. The results open up new possibilities for the investigation of
coherent many-body phenomena in dipolar Rydberg gases. As an example we
demonstrate the van der Waals blockade, a variant of the dipole blockade, for a
mesoscopic atom sample
Optimal trapping wavelengths of Cs molecules in an optical lattice
The present paper aims at finding optimal parameters for trapping of Cs
molecules in optical lattices, with the perspective of creating a quantum
degenerate gas of ground-state molecules. We have calculated dynamic
polarizabilities of Cs molecules subject to an oscillating electric field,
using accurate potential curves and electronic transition dipole moments. We
show that for some particular wavelengths of the optical lattice, called "magic
wavelengths", the polarizability of the ground-state molecules is equal to the
one of a Feshbach molecule. As the creation of the sample of ground-state
molecules relies on an adiabatic population transfer from weakly-bound
molecules created on a Feshbach resonance, such a coincidence ensures that both
the initial and final states are favorably trapped by the lattice light,
allowing optimized transfer in agreement with the experimental observation
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