Heteronuclear collisions between laser-cooled metastable neon atoms

Abstract

We investigate heteronuclear collisions in isotope mixtures of laser-cooled metastable ( 3 P2) neon. Experiments are performed with spin-polarized atoms in a magnetic trap for all two-isotope combinations of the stable neon isotopes 20 Ne, 21 Ne, and 22 Ne. We determine the rate coefficients for heteronuclear ionizing collisions to β21,20 = (3.9 ± 2.7) × 10 −11 cm 3 /s, β22,20 = (2.6 ± 0.7) × 10 −11 cm 3 /s, and β21,22 = (3.9 ± 1.9) × 10 −11 cm 3 /s. We also study heteronuclear elastic collision processes and give upper bounds for heteronuclear thermal relaxation cross sections. This work significantly extends the limited available experimental data on heteronuclear ionizing collisions for laser-cooled atoms involving one or more rare gas atoms in a metastable state. I. INTRODUCTIONDue to their high internal energy which surpasses the ionization energy of almost all neutral atomic and molecular collision partners, metastable rare-gas atoms (Rg*) prepared by laser cooling techniques [1] present a unique class of atoms for the investigation of cold and ultracold collisions [2]. With lifetimes ranging from 14.73 s (neon)[3] to 7870 s (helium) [4], the first excited metastable states present effective ground states for applying standard laser cooling techniques. The resulting extremely low kinetic energy of the laser-cooled atoms (≈ 10 −10 eV) stands in strong contrast to the high internal energy between 8 eV (xenon) and 20 eV (helium). This offers unique conditions not accessible with samples of lasercooled alkali-metal atoms. In particular, the high internal energy of the metastable state allows for Penning (PI) and associative (AI) ionizing collisions,to dominate losses in trapped Rg* samples at high densities. Since direct detection of the collision products (using electron multipliers) as well as of the remaining Rg* atoms is possible with high efficiency, detailed studies of homonuclear ionizing collisions have been carried out for all rare gas elements (see [1] for an overview). Additional motivation for these investigations arises from the fact, that favorable rate coefficients for inelastic but also for elastic collisions are essential for the achievement of quantum degeneracy which for Rg* atoms so far has only been demonstrated for 4 He [5-8] and 3 He [9]. For unpolarized Rg* samples, two-body loss rate coefficients for PI [10] between β = 6 × 10 −11 cm 3 /s for 132 Xe [11] and β = 1 × 10 −9 cm 3 /s for 22 Ne [12] have been measured. Spin polarizing the atoms to a spin-stretched * gerhard.birkl@physik.tu-darmstadt.de state may suppress PI: In a collision of atoms in spinstretched states the total spin of the reactants is larger than the total spin of the products. Thus, if spin is conserved, PI collisions should be significantly reduced. In the case of He* in the 3 S 1 state, a suppression of four orders of magnitude has been observed [7,13]. For the heavier rare gases, however, the metastable state 3 P 2 is formed by an exited s electron and a p 5 core with orbital momentum l = 1. This leads to an anisot...

Two-body loss rates for reactive collisions of cold atoms

“…Fitting these analytic two-body loss rates to available synthetic scattering data [27] on cold heteronuclear 20 Ne- 21 Ne collisions gives very good agreement and also matches the experimental data point of Ref. [11].…”

“…We also included the single available experimental data point from Ref. [11] to the picture. It can be seen that the pole expansion agrees very well with the synthetic data as well as with the experimental data point.…”

“…Current cold Ne* experiments of G. Birkl et al [10][11][12] have provided new data on elastic as well as inelastic scattering. The isotope composition of the Ne gas consists of the bosonic (B ) and fermionic (F) isotopes with natural abundance, i.e.…”

“…20 Ne (90.48%, B), 21 Ne (0.27%, F), 22 Ne (9.25%, B) [13]. Homonuclear [10,12] and heteronuclear collision rates [11] were obtained, preparing polarized as well as unpolarized subensembles with respect to the internal magnetic substates. The experiment uncovers deviations from a fundamental mass scaling law for the elastic and inelastic scattering rates of different isotopes.…”

Cold and trapped metastable noble gases

“…The innovations in the operation of MOTs for metastable noble gas atoms include the use of four beams rather than the usual six (Shimizu et al, 1991), the application of laser cooling light resonant with transitions to a higher lying state (Koelemeij et al, 2003Tychkov et al, 2004), in some cases applying Stark slowing instead of Zeeman slowing (Jung et al, 2003;Schumann et al, 1999), the simultaneous application of two-color laser fields for improved MOT performance (Kumakura and Morita, 1992;Rooijakkers et al, 1995Rooijakkers et al, , 1997a, as well as the simultaneous trapping of multiple-bosonic mixtures Schütz et al, 2011), BoseFermi mixtures Schütz et al, 2011;Stas et al, 2004), and metastable-alkali mixtures (Busch et al, 2006;Byron et al, 2010a,b;Sukenik and Busch, 2002).…”