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Register a new userObservation of heteronuclear atomic Efimov resonances
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The Efimov effect represents a cornerstone in few-body physics. Building on the recent experimental observation with ultracold atoms, we report the first experimental signature of Efimov physics in a heteronuclear system. A mixture of $^{41}$K and $^{87}$Rb atoms was cooled to few hundred nanoKelvins and stored in an optical dipole trap. Exploiting a broad interspecies Feshbach resonance, the losses due to three-body collisions were studied as a function of the interspecies scattering length. We observe an enhancement of the three-body collisions for three distinct values of the interspecies scattering lengths, both positive and negative. We attribute the two features at negative scattering length to the existence of two kind of Efimov trimers, namely KKRb and KRbRb.
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In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including atoms, molecules and nuclei, the characteristic spectrum of Efimov trimer states still eludes observation. Here we report on the discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behaviour, shedding new light onto the physics of few-body systems.
The field of few-body physics has originally been motivated by understanding nuclear matter. New model systems to experimentally explore few-body quantum systems can now be realized in ultracold gases with tunable interactions. Albeit the vastly different energy regimes of ultracold and nuclear matter (peV as compared to MeV), few-body phenomena are universal for near-resonant two-body interactions. Efimov states represent a paradigm for universal three-body states, and evidence for their existence has been obtained in measurements of three-body recombination in an ultracold gas of caesium atoms. Interacting samples of halo dimers can provide further information on universal few-body phenomena. Here we study interactions in an optically trapped mixture of such halo dimers with atoms, realized in a caesium gas at nanokelvin temperatures. We observe an atom-dimer scattering resonance, which we interpret as being due to a trimer state hitting the atom-dimer threshold. We discuss the close relation of this observation to Efimovs scenario, and in particular to atom-dimer Efimov resonances.
We report on the observation of ultracold heteronuclear Feshbach molecules. Starting with a $^{87}$Rb BEC and a cold atomic gas of $^{85}$Rb, we utilize previously unobserved interspecies Feshbach resonances to create up to 25,000 molecules. Even though the $^{85}$Rb gas is non-degenerate we observe a large molecular conversion efficiency due to the presence of a quantum degenerate $^{87}$Rb gas; this represents a key feature of our system. We compare the molecule creation at two different Feshbach resonances with different magnetic-field widths. The two Feshbach resonances are located at $265.44pm0.15$ G and $372.4pm1.3$ G. We also directly measure the small binding energy of the molecules through resonant magnetic-field association.
We study three- and four-body Efimov physics in a heteronuclear atomic system with three identical heavy bosonic atoms and one light atom. We show that exchange of the light atom between the heavy atoms leads to both three- and four-body features in the low-energy inelastic rate constants that trace to the Efimov effect. Further, the effective interaction generated by this exchange can provide an additional mechanism for control in ultracold experiments. Finally, we find that there is no true four-body Efimov effect - that is, no infinite number of four-body states in the absence of two- and three-body bound states - resolving a decades-long controversy.
We have observed three Feshbach resonances in collisions between lithium-6 and sodium-23 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 lithium-sodium 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.
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