Ultracold mixtures of metastable He and Rb: Scattering lengths from<i>ab initio</i>calculations and thermalization measurements

Knoop, Steven; Żuchowski, Piotr S.; Kędziera, Dariusz; Mentel, Ł. M.; Puchalski, Mariusz; Mishra, Hari Prasad; Flores, Adonis Silva; Vassen, W.

doi:10.1103/physreva.90.022709

Cited by 20 publications

(45 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Compared to Ref. [26], we have improved our atom number by increasing the MOT beam diameter from 1 to 2 inches. Afterward, we compress the cloud (the "cMOT" stage) by ramping down the detuning to −6 MHz in 10 ms, during which the power is reduced by a factor of ten, while keeping the same magnetic field gradient.…”

Section: Methodsmentioning

confidence: 99%

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

et al. 2015

View full text Add to dashboard Cite

Alternatively, one loads the atoms first in a magnetic trap and performs evaporative cooling and afterward transfers a dense and compact atomic cloud into an ODT, which now requires a much lower ODT power, at the expense of experimental complexity. Within this last category, a very elegant approach is the hybrid trap (HT), introduced in Ref.[1], consisting of a simple quadrupole magnetic trap (QMT) and a single-beam ODT. Efficient evaporation and BoseEinstein condensation (BEC) have been demonstrated (see, e.g., [1][2][3]), using ODT powers of only a few Watts. By switching off the QMT completely, the atoms are transferred from the HT to a pure ODT.The hybrid trap has been mostly applied to 87 Rb, but is assumed to be generally applicable to other magnetically trappable atomic species [1]. However, the application of HT strongly depends on the mass of atom. Most importantly, the rates of Majorana loss and heating, which determine the temperature that can be reached by evaporative cooling in a QMT, scale inversely with mass [4,5]. This limits the transfer efficiency for light atoms, or puts constraints on the trap volume and trap depth, and therefore the power, of the ODT. Furthermore, for light atoms evaporative cooling in the HT is limited as the additional axial confinement provided by the QMT is small because of the small levitation gradient, below which the QMT has to operate in the HT. Finally, the small levitation gradient puts experimental limits on the control of the displacement of the QMT with respect to the ODT, which further limits the axial confinement.Here we report on the production of a metastable triplet helium ( 4 He * ) BEC using a single-beam HT with a moderate power of less than 3 W, demonstrating the application of HT for a light atom. Our work provides a novel and simple method for obtaining a 4 He * BEC, which can be used for atom optics experiments [6][7][8][9][10] or precision spectroscopy Abstract We demonstrate a simple scheme to reach Bose-Einstein condensation (BEC) of metastable triplet helium atoms using a single-beam optical dipole trap with moderate power of less than 3 W. Our scheme is based on RF-induced evaporative cooling in a quadrupole magnetic trap and transfer to a single-beam optical dipole trap that is located below the magnetic trap center. We transfer 1 × 10 6 atoms into the optical dipole trap, with an initial temperature of 14 µK, and observe efficient forced evaporative cooling both in a hybrid trap, in which the quadrupole magnetic trap operates just below the levitation gradient, and in the pure optical dipole trap, reaching the onset of BEC with 2 × 10 5 atoms and a pure BEC of 5 × 10 4 atoms. Our work shows that a single-beam hybrid trap can be applied for a light atom, for which evaporative cooling in the quadrupole magnetic trap is strongly limited by Majorana spin-flips, and the very small levitation gradient limits the axial confinement in the hybrid trap.

show abstract

Section: Methodsmentioning

confidence: 99%

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

et al. 2015

View full text Add to dashboard Cite

show abstract

“…The latter largely varies with slight changes of the interaction potential. Due to inaccuracies in the state-of-the-art electronic calculations, only for very particular atom + atom systems [31][32][33] has it been possible to reproduce the experimental scattering length theoretically. As atom + diatom systems are even more complicated, it is difficult to assess the accuracy of calculations for ultracold energies.…”

mentioning

confidence: 99%

Beyond universality: Parametrizing ultracold complex-mediated reactions using statistical assumptions

et al. 2015

View full text Add to dashboard Cite

We have calculated accurate quantum reactive and elastic cross sections for the prototypical barrierless reaction D + + H 2 (v = 0, j = 0) using a modified hyperspherical scattering method. The considered kinetic energy ranges from the ultracold to the Langevin regimes. A reaction rate coefficient practically constant in no less than eight orders of magnitude is obtained. The availability of accurate results for this system allows one to test the quantum theory by Jachymski et al. [K. Jachymski, M. Krych, P. S. Julienne, and Z. Idziaszek, Phys. Rev. Lett. 110, 213202 (2013)] in a nonuniversal case. The short-range reaction probability is rationalized using statistical model assumptions and related to a statistical factor. This provides a means to estimate one of the parameters that characterizes ultracold processes from first principles. The increasing availability of cold and ultracold samples of atoms and molecules has sprung great interest in chemical reactions at very low temperatures [1][2][3][4][5]. Although new experimental approaches [5] appear highly promising, advances in the field are hampered by technical problems in producing most molecules at low temperatures and high enough densities. In contrast to neutral species, ions can be easily trapped and cooled. The technology of Coulomb crystals in radiofrequency ion traps [6] and the possibility of combining them with traps for neutrals or with slow molecular beams [7,8] promise great progress in the analysis of ion-neutral reactions in the near future.Theoretical simulations employing standard ab initio approaches are not feasible for most of the systems thus far considered. For heavy systems (more convenient experimentally) there are no potential energy surfaces (PESs) accurate enough to describe processes near thresholds. Additionally, most of exact dynamical treatments face insurmountable problems in such regimes. However, in contrast to short-range (SR) chemical interactions, those occurring at long range (LR) can be more easily calculated. Moreover, theoretical approaches based only on the knowledge of the LR part of the PES have been able to describe recent experimental findings nearly quantitatively [1,9]. Indeed, processes at very low collision energies favor LR interactions, leading to the idea of universality in extreme cases [10]: the result of the collision depends exclusively on the LR behavior and not on the details of the PES. In this regard, recently proposed LR parametrization procedures [9,[11][12][13] Fitting experimental data, these models are able to predict nonmeasured values providing some insight into the underlying interactions. In particular, the approach by Jachymski et al., based on multichannel quantum-defect theory (MQDT), provides analytical expressions which can be easily compared with experimental data [9,14,15]. The model has been recently applied to a variety of systems [9,16,17]. In particular, for the Penning ionization of Ar by He( 3 S) [5], the rate coefficients have been fitted in a wide range of collision ener...

show abstract

“…Previous experimental studies of He * +alkali collisions have been performed at thermal energies in stationary afterglow and merged-beam experiments (see e. g. [12,15] [16]. Magnetic trapping of the h + C spin-state combination, which is purely quartet, provided upper limits of the PI rate on the order of 10 −12 cm 3 s −1 for pure quartet scattering [13,17], and revealed a small quartet scattering length a Q [13], in agreement with ab initio calculations of the quartet 4 Σ + potential [13,18]. In contrast, the knowledge on the doublet 2 Σ + potential is limited [12], and the doublet scattering length a D is unknown.…”

mentioning

confidence: 99%

“…We use a fixed ODT power of 3.8 W, corresponding to an effective trap depth of 200 µK and 140 µK for He * and Rb, respectively [21]. Throughout the preparation stages in the QMT and ODT we use the stable h+C spin-state combination [13].…”

mentioning

confidence: 99%

See 1 more Smart Citation

Quantum-state-controlled Penning-ionization reactions between ultracold alkali-metal and metastable helium atoms

2016

Self Cite

View full text Add to dashboard Cite

In an ultracold, optically trapped mixture of 87 Rb and metastable triplet 4 He atoms we have studied trap loss for different spin-state combinations, for which interspecies Penning ionization is the main two-body loss process. We observe long trapping lifetimes for the purely quartet spinstate combination, indicating strong suppression of Penning ionization loss by at least two orders of magnitude. For the other spin-mixtures we observe short lifetimes that depend linearly on the doublet character of the entrance channel. We compare the extracted loss rate coefficient with recent predictions of multichannel quantum-defect theory for reactive collisions involving a strong exothermic loss channel and find near-universal loss for doublet scattering. Our work demonstrates control of Penning ionization reactive collisions by internal atomic state preparation.Ultracold inelastic and reactive collisions are important processes in atomic and molecular samples [1,2], determining their trapping lifetimes and the success of evaporative and sympathetic cooling. Conversely, measurements of these lifetimes reveal the rate coefficients of the dominant inelastic or reactive collision processes, opening the fields of ultracold few-body physics [3,4] and ultracold chemistry [5,6]. The ultracold regime offers exquisite control over the initial internal and external quantum states, and the possibility to experimentally control collision properties or even steer chemical reactions with external fields [7].Understanding of inelastic and reactive collisions is in general very difficult due to the many degrees of freedom involved. This has motivated recent work based on multichannel quantum-defect theory (MQDT) [8][9][10], in which analytic expressions of collision rates were derived in the case of a strong exothermic reactive channel. In particular, if the probability of an inelastic or reactive process in the short-range part of the collision is 100%, i. e. if P re = 1, theory predicts universal rate constants that only depend on the reduced mass of the collision partners and the leading long-range coefficient [8,9], independent of the complicated short-range dynamics. If the reaction probability is less than 100% (P re < 1), still only two parameters are required to include the (nonuniversal) short-range physics, i. e. the scattering length a and P re [10]. These analytical models have been applied to atom-exchange reactions between ground state KRb molecules below 1 µK [5,8], and Penning ionization reactions between argon and helium atoms in the metastable triplet 2 3 S 1 state (He * ) in merged-beam experiments from 10 mK up to 30 K [10,11].In this Rapid Communication we study ultracold Penning ionizing collisions between He * atoms (internal energy 19.8 eV) and alkali atoms A in their electronic ground state:

show abstract

Ultracold mixtures of metastable He and Rb: Scattering lengths fromab initiocalculations and thermalization measurements

Cited by 20 publications

References 52 publications

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

Simple method for producing Bose–Einstein condensates of metastable helium using a single-beam optical dipole trap

Beyond universality: Parametrizing ultracold complex-mediated reactions using statistical assumptions

Quantum-state-controlled Penning-ionization reactions between ultracold alkali-metal and metastable helium atoms

Contact Info

Product

Resources

About