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arXiv:1508.05405 · Physical Review A

Enhanced magnetic trap loading for atomic strontium

Daniel S. Barker, Benjamin J. Reschovsky, Neal C. Pisenti, Gretchen K. Campbell

Published Oct 26, 2015• 9 citations
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Abstract

We report on a technique to improve the continuous loading of atomic strontium into a magnetic trap from a magneto-optical trap. This is achieved by adding a depumping laser tuned to the $^{3}P_{1}\ensuremath{\rightarrow}^{3}S_{1}$ (688-nm) transition. The depumping laser increases atom number in the magnetic trap and subsequent cooling stages by up to 65% for the bosonic isotopes and up to 30% for the fermionic isotope of strontium. We optimize this trap loading strategy with respect to the 688-nm laser detuning, intensity, and beam size. To understand the results, we develop a one-dimensional rate equation model of the system, which is in good agreement with the data. We discuss the use of other transitions in strontium for accelerated trap loading and the application of the technique to other alkaline-earth-like atoms.

DOI
10.1103/physreva.92.043418

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arXiv:physics/0212024•Physical Review A•Jan 13, 2003•96 citations
We report on a technique to improve the continuous loading of atomic strontium into a magnetic trap from a magneto-optical trap. This is achieved by adding a depumping laser tuned to the 3P1\ensuremath→3S1^{3}P_{1}\ensuremath{\rightarrow}^{3}S_{1}3P1​\ensuremath→3S1​ (688-nm) transition. The depumping laser increases atom number in the magnetic trap and subsequent cooling stages by up to 65% for the bosonic isotopes and up to 30% for the fermionic isotope of strontium. We optimize this trap loading strategy with respect to the 688-nm laser detuning, intensity, and beam size. To understand the results, we develop a one-dimensional rate equation model of the system, which is in good agreement with the data. We discuss the use of other transitions in strontium for accelerated trap loading and the application of the technique to other alkaline-earth-like atoms.
We present a scheme to enhance the atom number in magneto-optical traps of strontium atoms operating on the 461-nm transition. This scheme consists of resonantly driving the ${}^{1}{\mathrm{S}}_{0}\ensuremath{\rightarrow}{}^{3}{\mathrm{P}}_{1}$ intercombination line at 689 nm, which continuously populates a short-lived reservoir state and, as expected from a theoretical model, partially shields the atomic cloud from losses arising in the 461-nm cooling cycle. We show a factor of 2 enhancement in the atom number for the bosonic isotopes 88Sr{}^{88}\mathrm{Sr}88Sr and 84Sr{}^{84}\mathrm{Sr}84Sr, and the fermionic isotope 87Sr{}^{87}\mathrm{Sr}87Sr, in good agreement with our model. Our scheme can be applied in the majority of strontium experiments without increasing the experimental complexity of the apparatus, since the employed 689-nm transition is commonly used for further cooling. Our method should thus be beneficial to a broad range of quantum science and technology applications exploiting cold strontium atoms, and could be extended to other atomic species.
We describe the operation and performance of an ultracold strontium apparatus that is capable of generating quantum degenerate gases. The experiment has produced Bose-Einstein condensates (BECs) of 84Sr and 86Sr as well as degenerate Fermi gases (DFGs) of 87Sr with a reduced temperature of T/TF = 0.2 at a Fermi temperature of TF = 55 nK. Straightforward modifications could be made to allow for isotopic mixtures and BECs of the fourth stable isotope, 88Sr. We also report on a technique to improve the continuous loading of a magnetic trap by adding a laser tuned to the 3P1 - 3S1 transition. The method increases atom number in the magnetic trap and subsequent cooling stages by up to 65% for the bosonic isotopes and up to 30% for the fermionic isotope of strontium. We optimize this trap loading strategy with respect to laser detuning, intensity, and beam size. To understand the results, we develop a one-dimensional rate equation model of the system, which is in good agreement with the data. We discuss the use of other transitions in strontium for accelerated trap loading and the application of the technique to other alkaline-earth-like atoms. Finally, we also report on an updated investigation of photoassociation resonances relative to the 1S0 + 3P1 dissassociation limit in bosonic strontium. Multiple new resonances for 84Sr and 86Sr were measured out to binding energies of -5 GHz and several discrepancies in earlier measurements were resolved. These measurements will allow for the development of a more accurate mass-scaled model and a better theoretical understanding of the molecular potentials near the 3P1 state. We also measure the strength of the 84Sr 0u transitions in order to characterize their use as optical Feshbach resonances.
We demonstrate enhanced loading of strontium atoms into a magneto-optical trap using a repumping scheme from the metastable state via the doubly excited state $5s5p{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{2}\ensuremath{\rightarrow}5{p}^{2}{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{2}$ at 481nm481\phantom{\rule{3.33333pt}{0ex}}\mathrm{nm}481nm. The number of trapped atoms is increased by an order of magnitude. The frequency and intensity dependence of the atom number enhancement, with respect to the nonrepumping case, is well reproduced by a simple rate equation model, which also describes single-laser repumping schemes reported previously. The repumping scheme is limited by a weak additional loss channel into the long-lived 5s5p3P05s5p{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{0}5s5p3P0​ state. For low repumping intensities, the signature of a halo formed by magnetically trapped atoms in the metastable state is found.
ABSTRACT In a ceramic vapor cell we have created a robust Sr magneto-optical trap that stores about 108 atoms with lifetimes>200 ms. We eliminate the 5p 1P1—4d 1D2—*5p 3P2 leak and achieve a 10-fold improvement in trap lifetime byrepumping the 5p 3Po,2 dark states with 679 nm and 707 nm light. The observed lifetime is now limited by coldcollision losses, and we have preliminary measurements of the 2-body loss rate. Direct readout of the trap velocity distribution is possible using the narrow (7 kHz) 52 'S0----5p 3P1 intercombination line at 689 nm. We can also cool with this narrow transition and have achieved a 40-fold 1-D velocity compression for about 5% of the trapped atoms by applying this second-stage cooling. Keywords: Laser cooling, laser trapping, alkaline earths, cold collisions, frequency metrology 1. INTRODUCTION Laser cooling and trapping techniques have advanced to become an important tool of the atomic physics community, and in recent years there has been considerable interest in expanding the range of trapped elements. The alkalineearths, in particular, possess unique characteristics which make them interesting to trap. Studies of long-rangeatom-atom interactions are simplified because they have no hyperfine structure, and their narrow intercombinationtransitions make them excellent candidates for optical frequency standards. Furthermore, Doppler cooling with thesenarrow transitions can reduce temperatures to near the recoil limit.The most abundant alkaline earth isotopes have I =
Spectroscopy of the 5s5p5s5p5s5p $ ^3 P_0 \rightarrow 5s5d$ $ ^3 D_1 $ transition of strontium using laser cooled atoms
This article presents spectroscopy results of the 5s5p  3P0→5s5d  3D15s5p{\;^3}P_0 \rightarrow 5s5d{\;^3}D_15s5p3P0​→5s5d3D1​ transition in all isotopes of laser cooled Sr atoms and the utility of this transition for repumping application. By employing the $5s5p{\;^{3} P_{0}} \rightarrow 5s5d{\;^3}D_1 $ (483 nm) transition in combination with the excitation of 5s5p  3P2→5s6s  3S15s5p{\;^3}P_2 \rightarrow 5s6s{\;^3}S_15s5p3P2​→5s6s3S1​ (707 nm) transition, we observe a significant increase (∼\sim∼ 13 fold) in the steady state number of atoms in the magneto-optic trap (MOT). This enhancement is attributed to the efficient repumping of Sr atoms that have decayed into the dark 5s5p  3P25s5p{\;^3}P_25s5p3P2​ state by returning them to the ground state 5s2  1S05s^2{\;^1}S_05s21S0​ without any loss into the other states. The absolute transition frequencies were measured with an absolute accuracy of 30 MHz. To support our measurements, we performed Fock-space relativistic coupled-cluster calculations of the relevant parameters in Sr. To further increase the accuracy of the calculated properties, corrections from the Breit, QED and perturbative triples were also included. The calculated branching ratio for the repumping state confirms the significantly increased population in the 3P1{^3}P_13P1​ state. Thereby, leading to an increase of population of atoms trapped due to the enhanced repumping. Our calculated hyperfine-splitting energies are in excellent agreement with the measured values. Moreover, our calculated isotope shifts in the transition frequencies are in good agreement with our measured values.
We report the magnetic trapping of metastable 3P2{}^{3}{P}_{2}3P2​ atomic strontium. Atoms are cooled in a magneto-optical trap (MOT) operating on the dipole-allowed ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ transition at 461 nm. Decay via ${}^{1}{\stackrel{\ensuremath{\rightarrow}}{{P}_{1}}}^{1}{\stackrel{\ensuremath{\rightarrow}}{{D}_{2}}}^{3}{P}_{2}$ continuously loads a magnetic trap formed by the quadrupole magnetic field of the MOT. Over 108{10}^{8}108 atoms at a density of $8\ifmmode\times\else\texttimes\fi{}{10}^{9}{\mathrm{cm}}^{\ensuremath{-}3}$ and temperature of 1 mK are trapped. The atom temperature is significantly lower than what would be expected from the kinetic and potential energies of atoms as they are transferred from the MOT. This suggests the occurrence of thermalization and evaporative cooling in the magnetic trap.