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Physical Review A

Measurement of the 3s3p P31 lifetime in magnesium using a magneto-optical trap

P. L. Hansen, Kasper T. Therkildsen, Nicola Malossi, Brian B. Jensen, Erik van Ooijen, Anders Brusch, Jörg Helge Müller, Jan Hald, Jan W. Thomsen

Published Jun 2, 2008• 11 citations
Publisher

Abstract

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 $(3s3p)\text{ }{^{3}P}_{1}$ 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 $(3{s}^{2})\text{ }{^{1}S}_{0}$ 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 $(3s3p)\text{ }{^{3}P}_{1}$ of $^{24}\text{M}\text{g}$. This lifetime has been measured numerous times previously, but with quite different results. Using our method we find the $(3s3p)\text{ }{^{3}P}_{1}$ 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.

DOI
10.1103/physreva.77.062502

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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.
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We present the first experimental determination of the electric-dipole forbidden $(3s3p)^{3}P_{2}\ensuremath{\rightarrow}(3{s}^{2})^{1}S_{0}$ (M2M2M2) transition rate in 24Mg^{24}\mathrm{Mg}24Mg and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each $^{3}P_{2}\ensuremath{\rightarrow}^{1}S_{0}$ decay event into millions of photons readily detected. The transition rate is determined to be $(4.87\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ corresponding to a 3P2^{3}P_{2}3P2​ lifetime of ${2050}_{\ensuremath{-}110}^{+140}$ sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment.
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