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arXiv:1412.2854 · Physical Review A

Core-shell magneto-optical trap for alkaline-earth-metal-like atoms

Jeongwon Lee, Jae Hoon Lee, Jiho Noh, Jongchul Mun

Published May 8, 2015• 39 citations
arXivHTMLPDF

Abstract

We propose and demonstrate a type of magneto-optical trap (MOT) for alkaline-earth-metal-like (AEML) atoms where the narrow intercombination ${}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{3}{P}_{1}$ transition and the broad ${}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{1}{P}_{1}$ transition are spatially arranged into a core-shell configuration. Our scheme resolves the main limitations of previously adopted MOT schemes for AEML atoms, leading to significant increases in both the loading rate and the steady-state atom number. We apply this scheme to our experimental setup with $^{174}\mathrm{Yb}$ atoms and observe more than two orders of magnitude improvement in the loading rate and tenfold improvement in the steady-state atom number compared to a conventional intercombination MOT scheme. This technique could be readily extended to other AEML atoms to increase the statistical sensitivity of many different types of precision experiments.

DOI
10.1103/physreva.91.053405

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We propose and demonstrate a type of magneto-optical trap (MOT) for alkaline-earth-metal-like (AEML) atoms where the narrow intercombination 1S0\ensuremath→3P1{}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{3}{P}_{1}1S0​\ensuremath→3P1​ transition and the broad 1S0\ensuremath→1P1{}^{1}{S}_{0}\ensuremath{\rightarrow}{}^{1}{P}_{1}1S0​\ensuremath→1P1​ transition are spatially arranged into a core-shell configuration. Our scheme resolves the main limitations of previously adopted MOT schemes for AEML atoms, leading to significant increases in both the loading rate and the steady-state atom number. We apply this scheme to our experimental setup with 174Yb^{174}\mathrm{Yb}174Yb atoms and observe more than two orders of magnitude improvement in the loading rate and tenfold improvement in the steady-state atom number compared to a conventional intercombination MOT scheme. This technique could be readily extended to other AEML atoms to increase the statistical sensitivity of many different types of precision experiments.
We report laser cooling and trapping of ytterbium atoms in a two-color magneto-optical trap (MOT). Benefited from both the broad singlet transition (1S0→1P1^1\text{S}_0\rightarrow {}^1\text{P}_11S0​→1P1​) and the narrow intercombination transition (1S0→3P1^1\text{S}_0\rightarrow {}^3\text{P}_11S0​→3P1​) of ytterbium atoms, the two-color MOT enables rapid loading and efficient cooling. We systematically investigate the shielding effect of the intercombination transition by examining the atom loading and loss rates of single-color and two-color MOTs. Our findings are general and can be extended to other alkaline earth(-like) atoms.
We describe the design, construction, and operation of a versatile dual-species Zeeman slower for both Cs and Yb, which is easily adaptable for use with other alkali metals and alkaline earths. With the aid of analytic models and numerical simulation of decelerator action, we highlight several real-world problems affecting the performance of a slower and discuss effective solutions. To capture Yb into a magneto-optical trap (MOT), we use the broad (1)S0 to (1)P1 transition at 399 nm for the slower and the narrow (1)S0 to (3)P1 intercombination line at 556 nm for the MOT. The Cs MOT and slower both use the D2 line (6(2)S1/2 to 6(2)P3/2) at 852 nm. The slower can be switched between loading Yb or Cs in under 0.1 s. We demonstrate that within a few seconds the Zeeman slower loads more than 10(9) Yb atoms and 10(8) Cs atoms into their respective MOTs. These are ideal starting numbers for further experiments on ultracold mixtures and molecules.
A steady-state magneto-optical trap (MOT) of fermionic strontium atoms operating on the 7.5-kHz7.5\text{-kHz}7.5-kHz-wide $^{1}S_{0}\text{\ensuremath{-}}^{3}P_{1}$ transition is demonstrated. This MOT contains $8.4\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.16em}{0ex}}\mathrm{atoms}$, a loading rate of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.16em}{0ex}}\mathrm{atoms}/\mathrm{s}$, and an average temperature of $12\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$. These parameters make it well suited to serve as a source of atoms for continuous-wave superradiant lasers operating on strontium's mHz-wide clock transition. Such lasers have only been demonstrated using pulsed Sr sources, limiting their range of applications. Our MOT makes an important step toward continuous operation of these devices, paving the way for continuous active optical clocks.
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We report the magneto-optical trapping of ytterbium atoms using the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{-}6s6p{}^{3}{P}_{1}$ intercombination transition. The magneto-optical trap is continuously loaded from an atomic beam decelerated by a Zeeman-tuned atomic-beam slower operated at the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{-}6s6p{}^{1}{P}_{1}$ transition. Among seven stable isotopes of ytterbium, six isotopes of170Yb,\mathrm{of}{ }^{170}\mathrm{Y}\mathrm{b},of170Yb, 171Yb,{}^{171}\mathrm{Yb},171Yb, 172Yb,{}^{172}\mathrm{Yb},172Yb, 173Yb,{}^{173}\mathrm{Yb},173Yb, 174Yb,{}^{174}\mathrm{Yb},174Yb, and 176Yb{}^{176}\mathrm{Yb}176Yb are successfully trapped. The number and density of the trapped atoms are about 108{10}^{8}108 and ${10}^{11} {\mathrm{cm}}^{\ensuremath{-}3},$ respectively. The temperature of atoms is estimated to be about $20 \ensuremath{\mu}\mathrm{K}$ from the time-of-flight measurement. The decay time of the trapped atoms after stopping the loading of atoms is about 3 s.
Alkaline-earth-metal atoms present an ideal platform for exploring magneto-optic trap (MOT) dynamics, enabling unique and definitive tests of laser cooling and trapping mechanisms. We have measured the trapping beam intensity, detuning, magnetic-field gradient, trap density, and lifetime dependence of the spring constant $\ensuremath{\kappa}$ and damping coefficient $\ensuremath{\alpha}$ for a ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ 88Sr{}^{88}\mathrm{Sr}88Sr MOT by fitting the oscillatory response of the atom cloud to a step-function force. We find that the observed behavior of $\ensuremath{\kappa}$ and $\ensuremath{\alpha}$ provide a unified and consistent picture of trap dynamics that agrees with Doppler cooling theory at the level of 1010%.10 Additionally, we demonstrate that the trapped atom temperature can be determined directly from measured value of $\ensuremath{\kappa}$ and the trap size, in excellent agreement with free-expansion temperature measurements. However, the experimentally determined temperature is much higher than Doppler cooling theory, implying significant additional heating mechanisms.