Physical Review A

Ultracold collisions and optical shielding in metastable xenon

Kalle‐Antti Suominen, Keith R. Burnett, Paul S. Julienne, M. Walhout, Uwe Sterr, Chad Orzel, Maarten D. Hoogerland, S. L. Rolston

Published Mar 1, 1996• 31 citations

Publisher

Abstract

Collisions between laser-cooled metastable xenon atoms in the presence of laser fields provide a good experimental test for ultracold collision theories as the observed ionization can be directly linked to the atomic binary collisions. Hyperfine structure is not present for the even isotopes ${\mathrm{Xe}}^{132}$ and ${\mathrm{Xe}}^{136}$, which simplifies the theoretical work. We present our results and show how these and the results presented in Walhout et al. [Phys. Rev. Lett. 74, 605 (1995)] can be interpreted with suitably adapted two-state models. Our approach suggests one possibility why the strong shielding of collisions predicted by the simple two-state model of Suominen et al. [Phys. Rev. A 51, 1446 (1995)] has not been achieved in the xenon experiment. \textcopyright{} 1996 The American Physical Society.

DOI: 10.1103/physreva.53.1678

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Physical Review A

Ultracold collisions and optical shielding in metastable xenon

Kalle‐Antti Suominen, Keith R. Burnett, Paul S. Julienne, M. Walhout, Uwe Sterr, Chad Orzel, Maarten D. Hoogerland, S. L. Rolston

Published Mar 1, 1996• 31 citations

Publisher

Abstract

{\mathrm{Xe}}^{132}

and

{\mathrm{Xe}}^{136}

, which simplifies the theoretical work. We present our results and show how these and the results presented in Walhout et al. [Phys. Rev. Lett. 74, 605 (1995)] can be interpreted with suitably adapted two-state models. Our approach suggests one possibility why the strong shielding of collisions predicted by the simple two-state model of Suominen et al. [Phys. Rev. A 51, 1446 (1995)] has not been achieved in the xenon experiment. \textcopyright{} 1996 The American Physical Society.

DOI: 10.1103/physreva.53.1678

Related papers

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M. Walhout, Henry J. L. Megens, A. Witte +1 more

We have magneto-optically trapped the nine stable isotopes of xenon. Using the Zeeman slowing method to decelerate a beam of xenon atoms in the metastable 6s 3/2 [3/2 ${]}_{2}$ state (notation representing nl ${\mathit{J}}_{\mathrm{core}}$ [K= ${\mathit{J}}_{\mathrm{core}}$ +l ${]}_{\mathit{J}}$ ), we load our trap to a collisionally limited density of more than ${10}^{10}$ atoms/ ${\mathrm{cm}}^{3}$ . The two odd isotopes are trapped without a repumping frequency, even though they have hyperfine structure. The sensitivity of the trapping process to the laser frequency is exploited to make accurate measurements of the isotope shifts for the 6s 3/2 [3/2 ${]}_{2}$ \ensuremath{\rightarrow}6p 3/2 [5/2 ${]}_{3}$ laser-cooling transition and of the hyperfine constants for $^{131}\mathrm{Xe}$ .We have magneto-optically trapped the nine stable isotopes of xenon. Using the Zeeman slowing method to decelerate a beam of xenon atoms in the metastable 6s 3/2 [3/2${]}_{2}$ state (notation representing nl ${\mathit{J}}_{\mathrm{core}}$ [K=${\mathit{J}}_{\mathrm{core}}$+l${]}_{\mathit{J}}$), we load our trap to a collisionally limited density of more than ${10}^{10}$ atoms/${\mathrm{cm}}^{3}$. The two odd isotopes are trapped without a repumping frequency, even though they have hyperfine structure. The sensitivity of the trapping process to the laser frequency is exploited to make accurate measurements of the isotope shifts for the 6s 3/2 [3/2${]}_{2}$\ensuremath{\rightarrow}6p 3/2 [5/2${]}_{3}$ laser-cooling transition and of the hyperfine constants for $^{131}\mathrm{Xe}$.

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{\mathrm{Xe}}^{132}

and

{\mathrm{Xe}}^{136}

Using 40 ns laser pulses, we probe the real-time dynamics of ultracold ionizing collisions in metastable xenon. We time resolve both shielding and enhancement effects, and observe the production of

{\mathrm{Xe}}_{2}^{+}

molecular ions through associative ionization. We estimate the rate of molecule formation in excited-state collisions, and directly measure the role of both flux enhancement and excited state survival in the collisional enhancement process. Conceptually simple theoretical models are used to predict the dynamics of the collisional shielding.

We have measured ultracold ionizing collision rates for three bosonic

{(}^{132}\mathrm{Xe},{}^{134}\mathrm{Xe},

and

{}^{136}\mathrm{Xe})

and two fermionic

{(}^{129}\mathrm{Xe}

and

{}^{131}\mathrm{Xe})

isotopes of xenon in the

6s[3/2{]}_{2}

metastable state, for both spin-polarized and unpolarized samples. For unpolarized samples at temperatures above the p-wave centrifugal barrier $(\ensuremath{\sim}39 \ensuremath{\mu}\mathrm{K}),$ we find that collision rates for all isotopes are identical. Quantum-statistical effects forbid s-wave collisions for spin-polarized fermions, giving rise to significant differences between bosonic and fermionic isotopes below the p-wave barrier. We present a technique for measuring collision rates at temperatures below $1 \ensuremath{\mu}\mathrm{K},$ and find that the ratio of polarized to unpolarized collision rates for fermions decreases by a factor of 2 at low temperatures, while the ratio for bosons increases by

50%.

We find no evidence of an overall reduction in the collision rate for spin-polarized samples, as has been observed in metastable helium. These results are explained using a simple theoretical model of transmission and quantum reflection off long-range interatomic potentials.

We present a theoretical and experimental investigation of homonuclear ionizing collisions of laser-cooled metastable

(2\phantom{\rule{0.2em}{0ex}}^{3}S_{1})

helium atoms, considering both the fermionic

^{3}\mathrm{He}

and bosonic

^{4}\mathrm{He}

isotopes. The theoretical description combines quantum threshold behavior, Wigner's spin-conservation rule, and quantum-statistical symmetry requirements in a single-channel model, complementing a more complete close-coupling theory that has been reported for collisions of metastable

^{4}\mathrm{He}

atoms. The model is supported with measurements (in the absence of light fields) of ionization rates in magneto-optically trapped samples that contain about $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms of a single isotope. The ionization rates are determined from measurements of trap loss due to light-assisted collisions combined with comparative measurements of the ion production rate in the absence and presence of trapping light. Theory and experiment show good agreement.

Ultracold ionizing collisions of laser-cooled Kr isotopes in the 1

{\mathit{s}}_{5}

[4${\mathit{p}}^{5}

5s

{:}^{3}$

{\mathit{P}}_{2}

] metastable state are investigated. When the collision energy is reduced below the p-wave centrifugal barrier of 80 \ensuremath{\mu}K, the ratio of the ionizing collision rate between polarized and unpolarized

^{83}\mathrm{Kr}

atoms is found to decrease. This is a direct evidence of the quantum interference of two identical Fermi particles. The experimental results are compared with the calculation based on the simplified inelastic collision theory.

We have magneto-optically trapped the nine stable isotopes of xenon. Using the Zeeman slowing method to decelerate a beam of xenon atoms in the metastable 6s 3/2 [3/2

{]}_{2}

state (notation representing nl

{\mathit{J}}_{\mathrm{core}}

[K=

{\mathit{J}}_{\mathrm{core}}

{]}_{\mathit{J}}

), we load our trap to a collisionally limited density of more than

{10}^{10}

atoms/

{\mathrm{cm}}^{3}

. The two odd isotopes are trapped without a repumping frequency, even though they have hyperfine structure. The sensitivity of the trapping process to the laser frequency is exploited to make accurate measurements of the isotope shifts for the 6s 3/2 [3/2

{]}_{2}

\ensuremath{\rightarrow}6p 3/2 [5/2

{]}_{3}

laser-cooling transition and of the hyperfine constants for

^{131}\mathrm{Xe}