Collisions between Tunable Halo Dimers: Exploring an Elementary Four-Body Process with Identical Bosons

Ferlaino, Francesca; Knoop, Steven; Mark, Manfred J.; Berninger, Martin; Schöbel, Harald; Nägerl, Hanns‐Christoph; Grimm, Rudolf

doi:10.1103/physrevlett.101.023201

Cited by 59 publications

(94 citation statements)

References 34 publications

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“…There has also been much progress in the measurement of rate coefficients of barrierless reactions involving alkali-metal atoms at cold and ultracold temperatures. This includes atom -molecule collisions such as Rb + Rb 2 [8,9], Cs + Cs 2 [10,11], Na + Na 2 [12], Rb/Cs + RbCs [13], and molecule -molecule collisions such as Cs 2 + Cs 2 [10,14], Na 2 + Na 2 [12], and Rb 2 + Rb 2 [9]. The typical rate coefficients of these reactions are on the order of 10 −11 − 10 −10 cm 3 molecule −1 s −1 depending on the collisional system, the temperature and the vibrational levels probed.…”

Section: Introductionmentioning

confidence: 99%

Formation of molecular oxygen in ultracoldO+OHcollisions

2009

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We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic and reactive cross sections as well as the vibrational and rotational populations of the product O2 molecules are reported. A J-shifting approximation is used to compute the rate coefficients. At temperatures T = 10 − 100 mK for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, T < 1 mK, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at T = 0.3 K, at higher temperatures, the quantum calculations predict a larger rate coefficient than the classical model, in agreement with experimental data for the O + OH reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about 6 × 10 −12 cm 3 molecule −1 s −1 , a value comparable to that of barrierless alkali-metal atom -dimer systems and about a factor of five larger than that of the tunneling dominated F + H2 reaction.

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Section: Introductionmentioning

confidence: 99%

Formation of molecular oxygen in ultracoldO+OHcollisions

2009

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“…[19]. By varying the magnetic field between 6 and 17 G, the scattering length a can be tuned from À1100 to 0a 0 [21], where a 0 is Bohr's radius.…”

Section: Selected For a Viewpoint In Physics P H Y S I C A L R E V I mentioning

confidence: 99%

“…In the a > 0 region, the dimer-atom-atom threshold (D þ A þ A) and the dimerdimer threshold (D þ D) are also depicted. The weakly bound dimer, only existing for a ) r vdW > 0, has universal halo character and its binding energy is given by @ 2 =ðma 2 Þ [2,19]. The open arrow marks the intersection of the first Efimov trimer (T) with the atomic threshold, while the filled arrows indicate the corresponding locations of the two universal tetramer states.…”

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Ultracold experiments strike universal physics—again

Esry¹

2009

Physics

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We report on the measurement of four-body recombination rate coefficients in an atomic gas. Our results obtained with an ultracold sample of cesium atoms at negative scattering lengths show a resonant enhancement of losses and provide strong evidence for the existence of a pair of four-body states, which is strictly connected to Efimov trimers via universal relations. Our findings confirm recent theoretical predictions and demonstrate the enrichment of the Efimov scenario when a fourth particle is added to the generic three-body problem. DOI: 10.1103/PhysRevLett.102.140401 PACS numbers: 03.75.Àb, 21.45.Àv, 34.50.Cx, 67.85.Àd Few-body physics produces bizarre and counterintuitive phenomena, with the Efimov effect representing the major paradigm of the field [1]. Early in the 1970s, Efimov found a solution to the quantum three-body problem, predicting the existence of an infinite series of universal weakly bound three-body states. Surprisingly, these Efimov trimers can even exist under conditions where a weakly bound dimer state is absent [2][3][4]. An essential prerequisite for the Efimov effect is a large two-body scattering length a, far exceeding the characteristic range of the interaction potential. Ultracold atomic systems with tunable interactions [5] have opened up unprecedented possibilities to explore such few-body quantum systems under well controllable experimental conditions. In particular, a can be made much larger than the van der Waals length r vdW [6], the range of the interatomic interaction.In the past few years, signatures of Efimov states have been observed in ultracold atomic and molecular gases of cesium atoms [7,8], and recently in three-component Fermi gases of 6 Li [9,10], in a Bose gas of 39 K atoms [11], and in mixtures of 41 K and 87 Rb atoms [12]. In all these experiments, Efimov states manifest themselves as resonantly enhanced losses, either in atomic three-body recombination or in atom-dimer relaxation processes.As a next step in complexity, a system of four identical bosons with resonant two-body interaction challenges our understanding of few-body physics. The extension of universality to four-body systems has been attracting increasing interest both in theory [13][14][15][16][17][18] and experiment [19]. A particular question under debate is the possible relation between universal three-and four-body states [13][14][15][16]18]. In this context, Hammer and Platter predicted the fourbody system to support universal tetramer states in close connection with Efimov trimers [16].Recently, von Stecher, D'Incao, and Greene presented key predictions for universal four-body states [18]. For each Efimov trimer, they demonstrate the existence of a pair of universal tetramer states according to the conjecture of Ref. [16]. Such tetramer states are tied to the corresponding trimer through simple universal relations that do not invoke any four-body parameter [13,15,18]. The authors of Ref.[18] suggest resonantly enhanced four-body recombination in an atomic gas as a probe for such universa...

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“…Here, there is a universal hierarchy of trimer states for resonant short-range interactions, while clusters of four or more bosons can also form [10][11][12][13]. Even in the limit of a 2D geometry, where the Efimov effect is absent, both trimers [14] and tetramers [15] have been predicted.…”

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Bound States in a Quasi-Two-Dimensional Fermi Gas

Levinsen

Parish

2013

Phys. Rev. Lett.

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We consider the problem of N identical fermions of mass m " and one distinguishable particle of mass m # interacting via short-range interactions in a confined quasi-two-dimensional (quasi-2D) geometry. For N ¼ 2 and mass ratios m " =m # < 13:6, we find non-Efimov trimers that smoothly evolve from 2D to 3D. In the limit of strong 2D confinement, we show that the energy of the N þ 1 system can be approximated by an effective two-channel model. We use this approximation to solve the 3 þ 1 problem and we find that a bound tetramer can exist for mass ratios m " =m # as low as 5 for strong confinement, thus providing the first example of a universal, non-Efimov tetramer involving three identical fermions. DOI: 10.1103/PhysRevLett.110.055304 PACS numbers: 67.85.Àd, 05.30.Fk, 34.50.Às An understanding of the few-body problem can be important for gaining insight into the many-body system. In dimensions higher than one, few-body bound states can, for instance, impact the statistics of the many-body quasiparticle excitations. Indeed, for fermionic systems, the two-body bound state is fundamental to the understanding of the BCS-BEC crossover [1][2][3][4], while the existence of three-body bound states of fermions [5,6] with unequal masses can lead to dressed trimer quasiparticles in the highly polarized Fermi gas [7]. Even in one dimension (1D), few-body bound states can impact the many-body phase: It has already been shown that one can have a Luttinger liquid of trimers [8].In general, attractively interacting bosons readily form bound clusters, with the celebrated example being the Efimov effect in 3D [9]. Here, there is a universal hierarchy of trimer states for resonant short-range interactions, while clusters of four or more bosons can also form [10][11][12][13]. Even in the limit of a 2D geometry, where the Efimov effect is absent, both trimers [14] and tetramers [15] have been predicted. On the other hand, bound states of identical fermions are constrained to have odd angular momentum owing to Pauli exclusion and thus, even for attractive interactions, identical fermions are subject to a centrifugal barrier. For short-range s-wave [16] interactions in 3D, non-Efimov trimers consisting of two identical fermions with mass m " and one distinguishable particle with mass m # can only exist above the critical mass ratio m " =m # ' 8:2 [5], while Efimov trimers only appear once m " =m # * 13:6 [17]. However, the existence of larger (N þ 1)-body bound states involving N > 2 identical fermions remains largely unknown-it has only recently been shown that Efimov tetramers exist in 3D [18].In this Letter, we investigate the problem of N identical fermions interacting with one distinguishable particle in a confined quasi-2D geometry, where the centrifugal barrier is reduced and the binding of fermions should be favored. Such 2D geometries have recently been realised in ultracold atomic Fermi gases [19][20][21][22][23], where the fermions are confined to 2D with an effective harmonic potential. In addition to allowing one to ...

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Collisions between Tunable Halo Dimers: Exploring an Elementary Four-Body Process with Identical Bosons

Cited by 59 publications

References 34 publications

Formation of molecular oxygen in ultracoldO+OHcollisions

Formation of molecular oxygen in ultracoldO+OHcollisions

Ultracold experiments strike universal physics—again

Bound States in a Quasi-Two-Dimensional Fermi Gas

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