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 [1,2]. 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 [2]. Efimov states represent a paradigm for universal three-body states [3], and evidence for their existence has been obtained in measurements of three-body recombination in an ultracold gas of caesium atoms [1]. Interacting samples of halo dimers [4] 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 Efimov's scenario [3], and in particular to atom-dimer Efimov resonances [5,6,7].Ultracold quantum gases offer an unprecedented level of control and are versatile systems to investigate interacting quantum systems. Their unique property is that the two-body interaction, as described by the s-wave scattering length a, can be magnetically tuned through Feshbach resonances [8,9,10]. When |a| is tuned to values much larger than the range of

Helium adsorbed on C 60 þ and C 70 þ exhibits phenomena akin to helium on graphite. Mass spectra suggest that commensurate layers form when all carbon hexagons and pentagons are occupied by one He each, but that the solvation shell does not close until 60 He atoms are adsorbed on C 60 þ , or 62 on C 70 þ . Molecular dynamics simulations of C 60 He n þ at 4 K show that the commensurate phase is solid. Helium added to C 60 He 32 þ will displace some atoms from pentagonal sites, leading to coexistence of a registered layer of immobile atoms interlaced with a nonregistered layer of mobile atoms.

We study inelastic collisions in a pure, trapped sample of Feshbach molecules made of bosonic cesium atoms in the quantum halo regime. We measure the relaxation rate coefficient for decay to lower-lying molecular states and study the dependence on scattering length and temperature. We identify a pronounced loss minimum with varying scattering length along with a further suppression of loss with decreasing temperature. Our observations provide insight into the physics of a few-body quantum system that consists of four identical bosons at large values of the two-body scattering length.

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The submersion of sodium clusters beyond a critical size in helium nanodroplets, which has recently been predicted on theoretical grounds, is demonstrated for the first time. Confirmation of a clear transition from a surface location, which occurs for alkali atoms and small clusters, to full immersion for larger clusters, is provided by identifying the threshold electron energy required to initiate Na n cluster ionization. On the basis of these measurements, a lower limit for the cluster size required for submersion, n ≥ 21, has been determined. This finding is consistent with the recent theoretical prediction.