Population distribution of product states following three-body recombination in an ultracold atomic gas

Härter, A.; Krükow, Artjom; Deiß, Markus; Drews, B.; Tiemann, E.; Denschlag, Johannes Hecker

doi:10.1038/nphys2661

Cited by 69 publications

(83 citation statements)

References 34 publications

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“…The comparison of the two rates then hinges on unknown numerical prefactors, and it becomes an experimental question whether losses dominate or a local equilibrium can be reached. In addition, we note that on resonance, the shallow bound state that exists for finite positive a disappears, so that loss requires atoms to decay to deeply bound molecular states [29]. For 85 Rb atoms, the previous experimental observation of a relatively narrow, and therefore long-lived, Efimov resonance (characterized by a dimensionless width, η = 0.057 ≪ 1) [11] is indicative that atoms close together do not decay instantaneously to deeply bound molecular states.…”

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confidence: 99%

Universal dynamics of a degenerate unitary Bose gas

et al. 2014

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From neutron stars to high-temperature superconductors, strongly interacting many-body systems at or near quantum degeneracy are a rich source of intriguing phenomena. The microscopic structure of the first-discovered quantum fluid, superfluid liquid helium, is difficult to access due to limited experimental probes. While an ultracold atomic Bose gas with tunable interactions (characterized by its scattering length, a) had been proposed as an alternative strongly interacting Bose system [1][2][3][4][5][6][7][8] , experimental progress [9][10][11][12] has been limited by its short lifetime. Here we present time-resolved measurements of the momentum distribution of a Bose-condensed gas that is suddenly jumped to unitarity, i.e. to a = ∞. Contrary to expectation, we observe that the gas lives long enough to permit the momentum to evolve to a quasi-steady-state distribution, consistent with universality, while remaining degenerate. Investigations of the time evolution of this unitary Bose gas may lead to a deeper understanding of quantum many-body physics.A powerful feature of atom gas experiments that provides access to these new regimes is the ability to change the interaction strength using a magnetic-field Feshbach resonance [13]. In particular, at the resonance location, a is infinite. For atomic Fermi gases [14][15][16][17][18][19][20], accessing this regime by adiabatically changing a led to the achievement of superfluids of paired fermions and enabled investigation of the crossover from superfluidity of weakly bound pairs, analogous to the Bardeen-Cooper-Schrieffer (BCS) theory of superconductors, to Bose-Einstein condensation (BEC) of tightly bound molecules [16,17]. For bosonic atoms, however, this route to strong interactions is stymied by the fact that three-body inelastic collisions increase as a to the fourth power [21][22][23]. This circumstance has limited experimental investigation of Bose gases with increasing interaction strength to studying either non-quantum-degenerate gases [24,25] or BECs with modest interaction strengths (na 3 < 0.008, where n is the atom number density) [9][10][11][12].The problem is that the loss rate scales as n 2 a 4 while the equilibration rate scales as na 2 v, where v is the average velocity. Thus, it would seem that the losses will always dominate as a is increased to ∞. Even if we were to forsake thermal equilibrium and suddenly change a in order to project a weakly interacting BEC onto strong interactions [12,[26][27][28], one might expect that three-body losses would still dominate the ensuing dynamics for large a. In this work, however, we use this approach to take a BEC to the unitary gas regime, and we observe dynamics that in fact saturate on a timescale shorter than that set by three-body losses and that exhibit universal scaling with density.

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Universal dynamics of a degenerate unitary Bose gas

et al. 2014

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“…One of the most advanced experiments in this direction is undoubtedly under progress in JILA at Boulder, where quantum threshold collisions induced by tunneling through a centrifugal barrier between fermionic ultracold KRb molecules have been detected [3,4] [9] have been detected through atom trap losses. Three-body recombination in a Rb quantum gas has been characterized [10], and features associated to universal N -body (up to N = 5) resonances induced by collisions between atoms and weaklybound molecules have been observed in quantum degenerate gases [11][12][13][14][15][16].However the deep understanding of the collisional dynamics is still to come as none of these achievements were able to characterize the nature and the state distribution of the final products [17,18]. The heavy mass of alkalimetal species leads to a huge density of resonant states related to the numerous rovibrational levels accessible during an atom/molecule or a molecule/molecule collision, preventing them to be individually characterized.…”

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“…Ultracold collisions between Cs atoms and Cs 2 [5,6] or LiCs [7] molecules, of Rb and Cs atoms with RbCs molecules [8], or of K and Rb atoms with KRb molecules [9] have been detected through atom trap losses. Three-body recombination in a Rb quantum gas has been characterized [10], and features associated to universal N -body (up to N = 5) resonances induced by collisions between atoms and weaklybound molecules have been observed in quantum degenerate gases [11][12][13][14][15][16].…”

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Theory of Long-Range Ultracold Atom-Molecule Photoassociation

2015

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The creation of ultracold molecules is currently limited to diatomic species. In this letter we present a theoretical description of the photoassociation of ultracold atoms and molecules to create ultracold excited triatomic molecules, thus being a novel example of light-assisted ultracold chemical reaction. The calculation of the photoassociation rate of ultracold Cs atoms with ultracold Cs2 molecules in their rovibrational ground state is reported, based on the solution of the quantum dynamics involving the atom-molecule long-range interactions, and assuming a model potential for the short-range physics. The rate for the formation of excited Cs3 molecules is predicted to be comparable with currently observed atom-atom photoassociation rates. We formulate an experimental proposal to observe this process relying on the available techniques of optical lattices and standard photoassociation spectroscopy.Ultracold dilute gases at temperatures much lower than 1 mK offer new opportunities for the study of elementary reactive processes between atoms and molecules. As emphasized in seminal review articles [1,2] this socalled ultracold chemistry is freed from averaging on large velocity distributions. Thus in this regime the quantum nature of the processes can be accessed, like the presence of resonances, or the sensitivity to long-range interactions which can induce anisotropic arrangements prior to the reaction. One of the most advanced experiments in this direction is undoubtedly under progress in JILA at Boulder, where quantum threshold collisions induced by tunneling through a centrifugal barrier between fermionic ultracold KRb molecules have been detected [3,4] [9] have been detected through atom trap losses. Three-body recombination in a Rb quantum gas has been characterized [10], and features associated to universal N -body (up to N = 5) resonances induced by collisions between atoms and weaklybound molecules have been observed in quantum degenerate gases [11][12][13][14][15][16].However the deep understanding of the collisional dynamics is still to come as none of these achievements were able to characterize the nature and the state distribution of the final products [17,18]. The heavy mass of alkalimetal species leads to a huge density of resonant states related to the numerous rovibrational levels accessible during an atom/molecule or a molecule/molecule collision, preventing them to be individually characterized. Models connecting the standard treatment of long-range interactions between particles to a statistical description of the resonances mostly resulting from short-range couplings have been developed [18][19][20][21]. The main quantitative uncertainty of such models arises from the estimation of the actual amount of resonant states which are indeed active during the collision.In this letter, we propose to use the well-known photoassociation (PA) process to get more insight into such collisions between ultracold atoms and molecules. PA of an ultracold atom pair is a laser-assisted collision creating an ...

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“…In particular, atomic ion-atom collisions, charge exchange collisions [6-10], sympathetic cooling of ions by ultracold trapped atoms [5,[10][11][12][13], three body reactions [14][15][16] and molecular ion formation processes [3,17] have been investigated. Two complementary directions motivate key goals for future work, (a) the low partial wave ionatom collisions which explores quantum scattering and many particle physics and (b), the controlled collisions between the cold molecular ions produced in the ionatom traps with co-trapped neutral atoms [18] and with light.…”

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Photodissociation of Trapped Rb2+ : Implications for Simultaneous Trapping of Atoms and Molecular Ions

et al. 2016

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The direct photodissociation of trapped 85 Rb + 2 (rubidium) molecular ions by the cooling light for the 85 Rb magneto-optical trap (MOT) is studied, both experimentally and theoretically. Vibrationally excited Rb + 2 ions are created by photoionization of Rb 2 molecules formed photoassociatively in the Rb MOT and are trapped in a modified spherical Paul trap. The decay rate of the trapped Rb + 2 ion signal in the presence of the MOT cooling light is measured and agreement with our calculated rates for molecular ion photodissociation is observed. The photodissociation mechanism due to the MOT light is expected to be active and therefore universal for all homonuclear diatomic alkali metal molecular ions.PACS numbers: Keywords:The spatially overlapped trapping of cold atoms and ions [1][2][3][4][5][6][7] has significantly expanded our ability to study interactions in cold, dilute gas ensembles. In particular, atomic ion-atom collisions, charge exchange collisions [6-10], sympathetic cooling of ions by ultracold trapped atoms [5,[10][11][12][13], three body reactions [14][15][16] and molecular ion formation processes [3,17] have been investigated. Two complementary directions motivate key goals for future work, (a) the low partial wave ionatom collisions which explores quantum scattering and many particle physics and (b), the controlled collisions between the cold molecular ions produced in the ionatom traps with co-trapped neutral atoms [18] and with light.A critical question which arises is whether the molecular ions can be trapped for a substantial extent of time simultaneously with an ensemble of cold atoms in order to study the interaction between them. In this letter, we address the possibility of simultaneous trapping of 85 Rb + 2 molecular ions with ultracold 85 Rb atoms in a magneto-optical trap (MOT). Our experimental observation shows that the cooling light for the Rb MOT leads to rapid destruction of the measured Rb + 2 ion signal. We measure the lifetime of trapped Rb + 2 in the presence of 780.2413 nm (≡ 12816.54 cm −1 ) light to be 495±80 ms. We discuss possible dissociation mechanisms and show that the experimental observation is in agreement with our theoretical calculations for the photodissociation of Rb + 2 molecular ions.The observed photodissociation mechanism is expected to be universal to all diatomic homonuclear alkali molecular ions as they exhibit similar potential energy characteristics.The experimental system consists of an ion-atom hybrid trap assembly as shown in Fig. 1. The detailed description of the experimental system can be found in ear- lier work [5,19,20]. Briefly, the hybrid trap consists of a MOT for atoms and a modified spherical Paul trap made of four tungsten wire loops in a square shape geometry for trapping ions. The ion trap radio frequency (rf) of 500 kHz with 150 V amplitude is applied to the inner pair of wires and a small (-5 V) constant potential is applied on the outer wires. The ion trap is operated at the optimal trapping voltage for Rb + 2 ions. For the expe...

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Population distribution of product states following three-body recombination in an ultracold atomic gas

Cited by 69 publications

References 34 publications

Universal dynamics of a degenerate unitary Bose gas

Universal dynamics of a degenerate unitary Bose gas

Theory of Long-Range Ultracold Atom-Molecule Photoassociation

Photodissociation of Trapped Rb2+ : Implications for Simultaneous Trapping of Atoms and Molecular Ions

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