Avalanche mechanism for atom loss near an atom-dimer Efimov resonance

Langmack, Christian; Smith, D. Hudson; Braaten, Eric

doi:10.1103/physreva.86.022718

Cited by 10 publications

(10 citation statements)

References 20 publications

(49 reference statements)

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“…In this model, each dimer produced in a three-body recombination collision shares its binding energy with multiple atoms as it leaves the trap volume due to the enhanced atom-dimer cross section [41]. Recent Monte Carlo calculations, however, conclude that the resulting peak from this avalanche mechanism is too broad and shifted to higher fields to explain the observations [43]. The remaining two features, a * 2,1 and a * 2,2 , are nominally located at dimer-dimer resonances, where the energy of a tetramer merges with the dimer-dimer threshold [39].…”

Section: (D)mentioning

confidence: 80%

Finite-range corrections near a Feshbach resonance and their role in the Efimov effect

2013

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We have measured the binding energy of 7 Li Feshbach molecules deep into the nonuniversal regime by associating atoms in a Bose-Einstein condensate with a modulated magnetic field. We extract the scattering length from these measurements, correcting for nonuniversal short-range effects using the field-dependent effective range. With this more precise determination of the Feshbach resonance parameters we reanalyze our previous data on the location of atom loss features produced by the Efimov effect [Pollack et al., Science 326, 1683]. We find the measured locations of the three-and four-body Efimov features to be consistent with universal theory at the 20%-30% level. Efimov showed more than 40 years ago that three particles interacting via resonant two-body interactions could form an infinite series of three-body bound states as the two-body s-wave scattering length a was varied [1]. In the limit of zero-range interactions, the ratios of scattering lengths corresponding to the appearance of each bound state were predicted to be a universal constant, equal to approximately 22.7. The only definitive observations of the Efimov effect have been in ultracold atoms, where the ability to tune a via a Feshbach resonance [2,3] has proven to be essential. Since the first evidence for Efimov trimers was obtained in ultracold Cs [4], experiments have revealed both three-and four-body Efimov states in several atomic species. Although the Efimov effect has now been confirmed, several open questions remain, including a full understanding of the role of nonuniversal finite-range effects. Accurate comparisons with theory require that these nonuniversal contributions be quantitatively determined and incorporated.We previously characterized the F = 1,m F = 1 Feshbach resonance in 7 Li, which is located at approximately 738 G, by extracting a from the measured size of trapped Bose-Einstein condensates (BEC) assuming a mean-field Thomas-Fermi density distribution [5,6]. These data were fit to obtain a(B), the function giving a versus magnetic field, which was used to assign values of a to Efimov features observed in the rate of inelastic three-and four-body loss of trapped atoms [5]. More recently, two groups have characterized the same Feshbach resonance by directly measuring the binding energy, E b , of the weakly bound dimers on the a > 0 side of the Feshbach resonance [7][8][9]. These measurements disagree with our previous measurements based on BEC size. The disagreement in the parameters characterizing the Feshbach parameters is sufficiently large to affect the comparison of the measured Efimov features with universal theory.In this paper, we report measurements of E b , which we fit to obtain a(B). The measurement of E b has fewer systematic uncertainties than the BEC size measurement, which is affected at large scattering length by beyond meanfield effects and by anharmonic contributions to the trapping potential. The extraction of a from E b can therefore be more accurate, and unlike the condensate size measurement, E b is r...

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Section: (D)mentioning

confidence: 80%

Finite-range corrections near a Feshbach resonance and their role in the Efimov effect

2013

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“…Those features are explained by secondary atom-dimer collisions that are resonantly enhanced near a = a * , where a * is the atom-dimer Efimov resonance position [1], which effectively leads to an enhancement of the number of atoms lost in a three-body recombination event. The precise underlying mechanism, and therefore what to extract from these additional resonances, is still under debate [35][36][37]. Here we note that if we take |a − |/r vdW = 8, then a * = 300a 0 , which is far away from the actual value 142a 0 , such that secondary atom-dimer collisions are expected not to play a role for 4 He * .…”

Section: Analysis Of Three-body Lossmentioning

confidence: 88%

Universal three-body parameter in ultracold4He*

et al. 2012

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We have analyzed our recently measured three-body loss rate coefficient for a Bose-Einstein condensate of spin-polarized metastable triplet 4 He atoms in terms of Efimov physics. The large value of the scattering length for these atoms, which provides access to the Efimov regime, arises from a nearby potential resonance. We find the loss coefficient to be consistent with the three-body parameter (3BP) found in alkali-metal experiments, where Feshbach resonances are used to tune the interaction. This provides evidence for a universal 3BP outside the group of alkali-metal elements. In addition, we give examples of other atomic systems without Feshbach resonances but with a large scattering length that would be interesting to analyze once precise measurements of three-body loss are available.

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“…The model of Ref. [50] predicts a very broad feature of moderately enhanced losses near a * . As it is experimentally very difficult to discriminate such a feature from the background, we cannot draw any conclusion on its presence.…”

Section: Search For An Atom-dimer Avalanche Effectmentioning

confidence: 97%

“…The energy released in a single recombination event is sufficient to kick several atoms out of the trap, which leads to enhanced losses. These measurements are still debated [49][50][51] as the atom-dimer peak position a * can only be inferred employing a collisional model. In this section, we present measurements obtained in pure atomic samples.…”

Section: Search For An Atom-dimer Avalanche Effectmentioning

confidence: 99%

Resonant atom-dimer collisions in cesium: Testing universality at positive scattering lengths

Zenesini

Berninger

et al. 2014

Phys. Rev. A

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We study the collisional properties of an ultracold mixture of cesium atoms and dimers close to a Feshbach resonance near 550 G in the regime of positive s-wave scattering lengths. We observe an atom-dimer loss resonance that is related to Efimov's scenario of trimer states. The resonance is found at a value of the scattering length that is different from a previous observation at low magnetic fields. This indicates nonuniversal behavior of the Efimov spectrum for positive scattering lengths. We compare our observations with predictions from effective field theory and with a recent model based on the van der Waals interaction. We present additional measurements on pure atomic samples in order to check for the presence of a resonant loss feature related to an avalanche effect, as suggested by observations in other atomic species. We could not confirm the presence of such a feature.A. ZENESINI et al. PHYSICAL REVIEW A 90, 022704 (2014)

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Avalanche mechanism for atom loss near an atom-dimer Efimov resonance

Cited by 10 publications

References 20 publications

Finite-range corrections near a Feshbach resonance and their role in the Efimov effect

Finite-range corrections near a Feshbach resonance and their role in the Efimov effect

Universal three-body parameter in ultracold4He*

Resonant atom-dimer collisions in cesium: Testing universality at positive scattering lengths

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