Beyond Born-Oppenheimer approximation in ultracold atomic collisions (original) (raw)
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Feshbach resonances in ultracold 39K
New Journal of Physics, 2007
We discover several magnetic Feshbach resonances in collisions of ultracold K(39) atoms, by studying atom losses and molecule formation. Accurate determination of the magnetic-field resonance locations allows us to optimize a quantum collision model for potassium isotopes. We employ the model to predict the magnetic-field dependence of scattering lengths and of near-threshold molecular levels. Our findings will be useful to plan future experiments on ultracold potassium atoms and molecules.
Observation of Feshbach resonances between two different atomic species
Physical Review Letters, 2004
We have observed three Feshbach resonances in collisions between 6 Li and 23 Na atoms. The resonances were identified as narrow loss features when the magnetic field was varied. The molecular states causing these resonances have been identified, and additional 6 Li-23 Na resonances are predicted. These resonances will allow the study of degenerate Bose-Fermi mixtures with adjustable interactions, and could be used to generate ultracold heteronuclear molecules.
2012
With use of Fano technique, we study collision of two atoms with formation of Feshbach resonance at combined interaction with the external magnetic field and laser radiation. In cases of one-and two-photon resonances of laser radiation with two discrete vibrational molecular levels, we show that Feshbach resonances appear at interaction of external magnetic field with dressed states formed via Autler-Townes effect. In addition, in case of one-photon resonance the lower vibrational molecular state is coupled by laser radiation with the continuum of the elastic channel and forms laser-induced Feshbach resonance via both Autler-Townes effect and LICS mechanism. We study the combined process of formation of Feshbach resonances; this enables the control of Feshbach resonance by varying the magnetic field and intensity and frequency of laser radiation. We also study the laserinduced inelastic collision and its influence on the considered processes. In case of two-photon resonance between discrete vibrational molecular states the Feshbach resonances arise under action of magnetic field via Autler-Townes effect, while the laser-induced transition into the elastic-channel continuum is in this case absent. We obtain the cross-sections of elastic and inelastic scattering and show that quenching of resonance occurs at the energy equal to that of the systems ground state. Dependence of the cross-sections on the magnetic field and laser intensity is examined in detail. In all considered cases, the scattering length is obtained and its dependence on the magnetic and laser fields is studied. In the absence of magnetic interaction if the hyperfine substates of the quasibound state in the closed channel and those of individual colliding atoms in the open channel are the same, Feshbach resonances may arise via weak interaction between nuclear and electronic motions, which leads to transitions between electronic states. The obtained results can be employed in new studies of collisions of cold atoms, e.g., of alkali metal atoms and for interpretation of new experiments in BECs.
Feshbach resonance in d-wave collisions
Physical Review A, 2009
We analyse a narrow Feshbach resonance with ultra-cold chromium atoms colliding in d-wave. The resonance is made possible by dipole-dipole interactions, which couple an incoming l = 2 collision channel with a bound molecular state with l = 0. We find that three-body losses associated to this resonance increase with temperature, and that the loss feature width as a function of magnetic field also increases linearly with temperature. The analysis of our experimental data shows that the Feshbach coupling is small compared both to the temperature and to the density limited lifetime of the resonant bound molecular state. One consequence is that the three body losse rate is proportionnal to the square of the number of atoms, and that we can directly relate the amplitude of the losses to the Feshbach coupling parameter. We compare our measurement to a calculation of the coupling between the collisionnal channel and the molecular bound state by dipole-dipole interactions, and find a good agreement, with no adjustable parameter. An analysis of the loss lineshape is also performed, which enables to precisely measure the position of the resonance.
Observation of Feshbach-Like Resonances in Collisions between Ultracold Molecules
Physical Review Letters, 2005
We observe magnetically tuned collision resonances for ultracold Cs2 molecules stored in a CO2laser trap. By magnetically levitating the molecules against gravity, we precisely measure their magnetic moment. We find an avoided level crossing which allows us to transfer the molecules into another state. In the new state, two Feshbach-like collision resonances show up as strong inelastic loss features. We interpret these resonances as being induced by Cs4 bound states near the molecular scattering continuum. The tunability of the interactions between molecules opens up novel applications such as controlled chemical reactions and synthesis of ultracold complex molecules.
We observe interspecies Feshbach resonances due to s-wave bound states in ultracold 39 K-133 Cs scattering for three different spin mixtures. The resonances are observed as joint atom loss and heating of the K sample. We perform least-squares fits to obtain improved K-Cs interaction potentials that reproduce the observed resonances, and carry out coupled-channel calculations to characterize the scattering and bound-state properties for 39 K-Cs, K-Cs and 41 K-Cs. Our results open up the possibilities of tuning interactions in K-Cs atomic mixtures and of producing ultracold KCs molecules. PACS numbers: 34.50.Cx, 34.20.Cf, 67.60.Bc
Feshbach spectroscopy of a K-Rb atomic mixture
Physical Review A, 2006
We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic 40K and bosonic 87Rb atoms. The magnetic-field locations of 14 interspecies resonances is used to construct a quantum collision model able to predict accurate collisional parameters for all K-Rb isotopic pairs. In particular we determine the interspecies s-wave singlet and triplet scattering lengths for the 40K-87Rb mixture as -111 +/- 5 Bohr and -215 +/- 10 Bohr respectively. We also predict accurate scattering lengths and position of Feshbach resonances for the other K-Rb isotopic pairs. We discuss the consequences of our results for current and future experiments with ultracold K-Rb mixtures.
Collision Properties of Ultracold ^133\mathrmCs$ Atoms
We present a theoretical analysis of numerous magnetically tunable Feshbach resonances measured by Chin et al. [ preceding Letter, Phys. Rev. Lett. 85, 2717] at fields of up to 25 mT. This analysis provides the most accurate characterization of the collisional properties of ground state Cs atoms currently available and clearly shows, in contrast to previous work, that Bose-Einstein condensation of 133 Cs cannot be ruled out. The X 1 S 1 g and a 3 S u scattering lengths are constrained to ͑280 6 10͒a 0 and ͑2400 6 100͒a 0 , respectively (1a 0 0.052 917 7 nm), and the van der Waals C 6 coefficient to 6890 6 35 a.u. ͑1 a.u. 0.095 734 5 3 10 224 J ? nm 6 ͒.