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arXiv:0812.3800 · Physical Review A

Measurement of the spin-forbidden decay rate (3s3d)1D2→(3s3p)P32,1 in M24g

Kasper T. Therkildsen, Brian B. Jensen, C. P. Ryder, Nicola Malossi, Jan W. Thomsen

Published Mar 24, 2009• 4 citations
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Abstract

We have measured the spin-forbidden decay rate from $(3s3d){^{1}D}_{2}\ensuremath{\rightarrow}(3s3p){^{3}P}_{2,1}$ in $^{24}\text{M}\text{g}$ atoms trapped in a magneto-optical trap. The total decay rate, summing up both exit channels $(3s3p){^{3}P}_{1}$ and $(3s3p){^{3}P}_{2}$, yields $196\ifmmode\pm\else\textpm\fi{}10\text{ }{\text{s}}^{\ensuremath{-}1}$ in excellent agreement with resent relativistic many-body calculations of Porsev et al. [Phys. Rev. A 64, 012508 (2001)]. The characterization of this decay channel is important as it may limit the performance of quantum optics experiments carried out with this ladder system as well as two-photon cooling experiments currently explored in several groups.

DOI
10.1103/physreva.79.034501

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We have measured the spin-forbidden decay rate from (3s3d)1D2\ensuremath→(3s3p)3P2,1(3s3d){^{1}D}_{2}\ensuremath{\rightarrow}(3s3p){^{3}P}_{2,1}(3s3d)1D2​\ensuremath→(3s3p)3P2,1​ in 24Mg^{24}\text{M}\text{g}24Mg atoms trapped in a magneto-optical trap. The total decay rate, summing up both exit channels (3s3p)3P1(3s3p){^{3}P}_{1}(3s3p)3P1​ and (3s3p)3P2(3s3p){^{3}P}_{2}(3s3p)3P2​, yields 196\ifmmode±\else\textpm\fi10 s\ensuremath−1196\ifmmode\pm\else\textpm\fi{}10\text{ }{\text{s}}^{\ensuremath{-}1}196\ifmmode±\else\textpm\fi10 s\ensuremath−1 in excellent agreement with resent relativistic many-body calculations of Porsev et al. [Phys. Rev. A 64, 012508 (2001)]. The characterization of this decay channel is important as it may limit the performance of quantum optics experiments carried out with this ladder system as well as two-photon cooling experiments currently explored in several groups.
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We explore the efficacy of optical pumping on the $5s4d\phantom{\rule{0.16em}{0ex}}^{1}D_{2}\text{\ensuremath{-}}5s8p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}$ (448nm)(448\phantom{\rule{0.16em}{0ex}}\mathrm{nm})(448nm) transition in a magneto-optical trap (MOT) of Sr atoms. The number of trapped atoms is enhanced by a factor of 12.0(6)12.0(6)12.0(6) relative to the case without repumping light, which is six times as large as that obtained using the pumping transition $5s4d\phantom{\rule{0.16em}{0ex}}^{1}D_{2}\text{\ensuremath{-}}5s6p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}$ (717nm)(717\phantom{\rule{0.16em}{0ex}}\mathrm{nm})(717nm). This enhancement is limited by decay pathways that bypass the 5s4d1D25s4d\phantom{\rule{0.16em}{0ex}}^{1}D_{2}5s4d1D2​ state, namely $5s5p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}\ensuremath{\rightarrow}5s4d\phantom{\rule{0.16em}{0ex}}^{3}D_{1}\ensuremath{\rightarrow}5s5p\phantom{\rule{0.16em}{0ex}}^{3}P_{0}$ and $5s5p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}\ensuremath{\rightarrow}5s4d\phantom{\rule{0.16em}{0ex}}^{3}D_{2}\ensuremath{\rightarrow}5s5p\phantom{\rule{0.16em}{0ex}}^{3}P_{2}$, which account for 8% of the total loss of the trapped atoms. We determine the decay rates for the $5s5p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}\ensuremath{\rightarrow}5s4d\phantom{\rule{0.16em}{0ex}}^{3}D_{1}$ and $5s5p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}\ensuremath{\rightarrow}5s4d\phantom{\rule{0.16em}{0ex}}^{3}D_{2}$ transitions to be $66(6)\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and $2.4(2)\ifmmode\times\else\texttimes\fi{}{10}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, respectively. Furthermore, we experimentally demonstrate, when the trap beam diameter is small, escape of atoms in the 5s4d1D25s4d\phantom{\rule{0.16em}{0ex}}^{1}D_{2}5s4d1D2​ state, which has a relatively long lifetime of $400\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{s}$, becomes a dominant loss mechanism, and that the 448nm448\phantom{\rule{0.16em}{0ex}}\mathrm{nm}448nm pumping light effectively suppresses this escape. Our findings will contribute to improved laser cooling and fluorescence imaging in cold strontium atom platforms, such as quantum computers based on optical tweezer arrays.
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Radiative decay from the excited 1P1{}^{1}\phantom{\rule{-0.16em}{0ex}}{P}_{1}1P1​ state to metastable 3P2{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{2}3P2​ and 3P0{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{0}3P0​ states is expected to limit the attainable trapped atomic population in a magneto-optic trap of ytterbium (Yb) atoms. In experiments we have carried out with optical repumping of 3P0,2{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{0,2}3P0,2​ states to 3P1{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{1}3P1​, we observe an enhanced yield of trapped atoms in the excited 1P1{}^{1}\phantom{\rule{-0.16em}{0ex}}{P}_{1}1P1​ state. The individual decay rate to each metastable state is measured and the results show excellent agreement with the theoretical 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.
We demonstrate an accurate method for measuring the lifetime of long-lived metastable magnetic states using a magneto-optical trap (MOT). Through optical pumping, the metastable (3s3p) 3P1(3s3p)\text{ }{^{3}P}_{1}(3s3p) 3P1​ level is populated in a standard MOT. During the optical pumping process, a fraction of the population is captured in the magnetic quadrupole field of the MOT. When the metastable atoms decay to the (3s2) 1S0(3{s}^{2})\text{ }{^{1}S}_{0}(3s2) 1S0​ ground state they are recaptured into the MOT. In this system no alternative cascading transition is possible. The lifetime of the metastable level is measured directly as an exponential load time of the MOT. We have experimentally tested our method by measuring the lifetime of the (3s3p) 3P1(3s3p)\text{ }{^{3}P}_{1}(3s3p) 3P1​ of 24Mg^{24}\text{M}\text{g}24Mg. This lifetime has been measured numerous times previously, but with quite different results. Using our method we find the (3s3p) 3P1(3s3p)\text{ }{^{3}P}_{1}(3s3p) 3P1​ lifetime to be $(4.4\ifmmode\pm\else\textpm\fi{}0.2)\text{ }\text{ms}$. Theoretical values point toward a lower value for the lifetime.