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arXiv:1908.10433 · Physical Review A

Enhancing the capture velocity of a Dy magneto-optical trap with two-stage slowing

William D. M. Lunden, Li Du, Michael Cantara, Pierre Barral, Alan O. Jamison, Wolfgang Ketterle

Published Jun 12, 2020• 30 citations
arXivHTMLPDF

Abstract

Magneto-optical traps (MOTs) based on the 626-nm, 136-kHz-wide intercombination line of Dy, which has an attractively low Doppler temperature of $3.3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$, have been implemented in a growing number of experiments over the last several years. A challenge in loading these MOTs comes from their low capture velocities. Slowed atomic beams can spread out significantly during free flight from the Zeeman slower to the MOT position, reducing the fraction of the beam captured by the MOT. Here we apply a scheme for enhancing the loading rate of the MOT wherein atoms are Zeeman slowed to a final velocity larger than the MOT's capture velocity and then undergo a final stage of slowing by a pair of near-detuned beams addressing the 421-nm transition directly in front of the MOT. By reducing the free-flight time of the Zeeman-slowed atomic beam, we greatly enhance the slowed flux delivered to the MOT, leading to more than an order-of-magnitude enhancement in the final MOT population.

DOI
10.1103/physreva.101.063403

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Magneto-optical traps (MOTs) based on the 626-nm, 136-kHz-wide intercombination line of Dy, which has an attractively low Doppler temperature of 3.3\ensuremathμK3.3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}3.3\ensuremathμK, have been implemented in a growing number of experiments over the last several years. A challenge in loading these MOTs comes from their low capture velocities. Slowed atomic beams can spread out significantly during free flight from the Zeeman slower to the MOT position, reducing the fraction of the beam captured by the MOT. Here we apply a scheme for enhancing the loading rate of the MOT wherein atoms are Zeeman slowed to a final velocity larger than the MOT's capture velocity and then undergo a final stage of slowing by a pair of near-detuned beams addressing the 421-nm transition directly in front of the MOT. By reducing the free-flight time of the Zeeman-slowed atomic beam, we greatly enhance the slowed flux delivered to the MOT, leading to more than an order-of-magnitude enhancement in the final MOT population.
We report on a scheme for loading dysprosium atoms into a narrow-line three-dimensional magneto-optical trap (3D MOT). Our approach replaces the conventional Zeeman slower with a two-dimensional (2D) MOT operating on the broad 421-nm line to create a high-flux beam of slow atoms. Even in the absence of a push beam, we demonstrate efficient loading of the 3D MOT, which operates on the narrower 626-nm intercombination line. Adding push beams working at either 421 nm or 626 nm, significant enhancement of the loading rate is achieved. We reach the best performance, with an enhancement factor of 3.6, using a push beam red-detuned to the 626-nm line. With loading rates greater than 108atoms/s{10}^{8}\phantom{\rule{0.16em}{0ex}}\text{atoms/s}108atoms/s achieved at a moderate oven reservoir temperature of ${800}^{\ensuremath{\circ}}\phantom{\rule{0.16em}{0ex}}\mathrm{C}$, our method offers similar or greater performance than Zeeman-slower-based systems. Our 2D-MOT-based approach constitutes a promising first step towards state-of-the-art quantum gas experiments with several advantages over the Zeeman-slower-based setup and is readily adaptable to other open-shell lanthanides.
We demonstrate a method to enhance the atom loading rate of a ytterbium (Yb) magneto-optic trap (MOT) operating on the 556 nm 1S0 → 3P1 intercombination transition (narrow linewidth Γg = 2π × 182 kHz). Following traditional Zeeman slowing of an atomic beam near the 399 nm 1S0 → 1P1 transition (broad linewidth Γp = 2π × 29 MHz), two laser beams in a crossed-beam geometry, frequency tuned near the same transition, provide additional slowing immediately prior to the MOT. Using this technique, we observe an improvement by a factor of 6 in the atom loading rate of a narrow-line Yb MOT. The relative simplicity and generality of this approach make it readily adoptable to other experiments involving narrow-line MOTs. We also present a numerical simulation of this two-stage slowing process, which shows good agreement with the observed dependence on experimental parameters, and use it to assess potential improvements to the method.
We describe an experimental setup for producing a large cold erbium (Er) sample in a narrow-line magneto-optical trap (MOT) in a simple and efficient way. We implement a pair of angled slowing beams with respect to the Zeeman slower axis, and further slow down atoms exiting from the Zeeman slower. The second-stage slowing beams enable the narrow-line MOT to trap atoms exiting from the Zeeman slower with higher velocity. This scheme is particularly useful when the Zeeman slower is at low optical power without the conventional transverse cooling between an oven and a Zeeman slower, in which case we significantly improve the loading efficiency into the MOT and are able to trap more than 108{10}^{8}108 atoms in the narrow-line MOT of 166Er^{166}\mathrm{Er}166Er. This work highlights our implementation, which greatly simplifies laser cooling and trapping of Er atoms and also should benefit other similar elements.
We report on building a pulsed source of cold Tm atoms and loading of the narrow-line magneto-optical trap (MOT) from the cold atomic beam. We achieve the loading rate of the first-stage MOT in the primary chamber up to 108 atoms/s and obtain a cold atomic beam with the mean longitudinal velocity ∼10 m/s and an angular spread of 18 mrad in a pulsed mode. In this regime, we can form a cold atomic beam with up to 5 × 106 atoms at a 5 Hz repetition rate. We also introduce a novel method to enhance the capture velocity of the narrow-line MOT by incorporating an additional axial cooling beam and achieve loading efficiency η = 10% of the second-stage MOT in the science chamber. Our approach could be extended to other atomic species with similar properties, such as Sr, Yb, Dy, and Er, serving as a convenient alternative for the traditional 2D-MOT schemes. Providing rapid loading of the MOT in the science chamber, it would reduce preparation time of the atomic ensemble leading to a shorter dead time in spectroscopy experiments and a higher repetition rate.
A significant enhancement in the number of cold atoms in an atomic-beam-loaded magneto-optical trap (MOT) for metastable krypton atoms is observed when hollow laser beams are used in a Zeeman slower instead of a Gaussian laser beam. In the Zeeman slower setup, a combination of two hollow laser beams, i.e., a variable-diameter hollow beam generated using a pair of axicon lenses superimposed on a fixed-diameter hollow beam, has been used to reduce the longitudinal velocity of the atoms in the atomic beam below the capture speed of the MOT. The observed enhancement in the number of atoms in the MOT is attributed to reduced destruction of the atom cloud in the MOT and increased cooling of the off-axis atoms in the atomic beam, resulting from the use of hollow beams in the Zeeman slower.
Abstract Recent experiments have demonstrated direct cooling and trapping of diatomic and triatomic molecules in magneto-optical traps (MOTs). However, even the best molecular MOTs to date still have density 10−5 times smaller than in typical atomic MOTs. The main limiting factors are: (i) inefficiencies in slowing molecules to velocities low enough to be captured by the MOT, (ii) low MOT capture velocities, and (iii) limits on density within the MOT resulting from sub-Doppler heating (Devlin and Tarbutt 2018 Phys. Rev. A 90 063415). All of these are consequences of the need to drive ‘Type-II’ optical cycling transitions, where dark states appear in Zeeman sublevels, in order to avoid rotational branching. We present simulations demonstrating ways to mitigate each of these limitations. This should pave the way toward loading molecules into conservative traps with sufficiently high density and number to evaporatively cool them to quantum degeneracy.