Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

An optical trap for Chromium atoms

Radu Chicireanu, Quentin Beaufils, A. Pouderous, B. Laburthe-Tolra, É. Maréchal, L. Vernac, J. Keller, O. Gorceix

Published Jun 1, 2007• 0 citations

Abstract

Our recent experiments demonstrate the continuous accumulation and thermalisation of up to 5ldr10752Cr atoms in a finite-depth magnetic quadrupole trap. Chromium possesses metastable dark states, in which atoms can be accumulated and which are shielded from the light-assisted inelastic collisions, activated by the MOT.

DOI: 10.1109/cleoe-iqec.2007.4386717

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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

An optical trap for Chromium atoms

Radu Chicireanu, Quentin Beaufils, A. Pouderous, B. Laburthe-Tolra, É. Maréchal, L. Vernac, J. Keller, O. Gorceix

Published Jun 1, 2007• 0 citations

Publisher

Abstract

DOI: 10.1109/cleoe-iqec.2007.4386717

Related papers

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We study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (rf) field. Chromium atoms $(^{52}\mathrm{Cr})$ in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In the presence of a rf field, the temperature of the metastable atoms that remain magnetically trapped can be as low as $25\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{K}$, with a density of ${10}^{17}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$, resulting in an increase of the phase-space density, still limited to $7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the rf-truncated magnetic trap, and deduce the average elastic cross section for atoms in the $^{5}D_{4}$ metastable states, ${\ensuremath{\sigma}}_{el}=7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$.We study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (rf) field. Chromium atoms $(^{52}\mathrm{Cr})$ in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In the presence of a rf field, the temperature of the metastable atoms that remain magnetically trapped can be as low as $25\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{K}$, with a density of ${10}^{17}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$, resulting in an increase of the phase-space density, still limited to $7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the rf-truncated magnetic trap, and deduce the average elastic cross section for atoms in the $^{5}D_{4}$ metastable states, ${\ensuremath{\sigma}}_{el}=7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$.

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We have constructed a magneto-optical trap for chromium atoms. Using trapping light at 425 nm and two repumping lasers tuned to intercombination transitions, over ${10}^{6}$ atoms were trapped and average densities of over ${10}^{16}{\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$ were obtained. Nonexponential loss of atoms is observed at high densities indicating inelastic collisions between trapped atoms. Over a range of trapping conditions, the density-dependent trap loss rate constant \ensuremath{\beta} is extracted from fluorescence decay curves and found to have values in the range of ${10}^{\ensuremath{-}15}{\mathrm{m}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1},$ much larger than is observed in alkali-metal traps.We have constructed a magneto-optical trap for chromium atoms. Using trapping light at 425 nm and two repumping lasers tuned to intercombination transitions, over ${10}^{6}$ atoms were trapped and average densities of over ${10}^{16}{\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$ were obtained. Nonexponential loss of atoms is observed at high densities indicating inelastic collisions between trapped atoms. Over a range of trapping conditions, the density-dependent trap loss rate constant \ensuremath{\beta} is extracted from fluorescence decay curves and found to have values in the range of ${10}^{\ensuremath{-}15}{\mathrm{m}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1},$ much larger than is observed in alkali-metal traps.

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(^{52}\mathrm{Cr})

in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In the presence of a rf field, the temperature of the metastable atoms that remain magnetically trapped can be as low as $25\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{K}$, with a density of ${10}^{17}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$, resulting in an increase of the phase-space density, still limited to $7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the rf-truncated magnetic trap, and deduce the average elastic cross section for atoms in the

^{5}D_{4}

metastable states, ${\ensuremath{\sigma}}_{el}=7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$.

We have realized a scheme for continuous loading of a magnetic trap (MT).

{}^{52}\mathrm{Cr}

atoms are continuously captured and cooled in a magneto-optical trap (MOT). Optical pumping to a metastable state decouples atoms from the cooling light. Due to their high magnetic moment $(6 {\ensuremath{\mu}}_{B}),$ low-field seeking metastable atoms are trapped in the magnetic quadrupole field provided by the MOT. Limited by inelastic collisions between atoms in the MOT and in the MT, we load

{10}^{8}

metastable atoms at a rate of

{10}^{8}

atoms/s below $100 \ensuremath{\mu}\mathrm{K}$ into the MT. Optical repumping after the loading allows us to realize a MT of ground-state chromium atoms.

We report on magneto-optical trapping of fermionic

^{53}\mathrm{Cr}

atoms. A Zeeman-slowed atomic beam provides loading rates up to $3\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. We present systematic characterization of the magneto-optical trap (MOT). We obtain up to $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms in the steady-state MOT. The atoms radiatively decay from the excited

P

state into metastable

D

states, and, due to the large dipolar magnetic moment of chromium atoms in these states, they can remain magnetically trapped in the quadrupole field gradient of the MOT. We study the accumulation of metastable

^{53}\mathrm{Cr}

atoms in this magnetic trap. We also report on the simultaneous magneto-optical trapping of bosonic

^{52}\mathrm{Cr}

and fermionic

^{53}\mathrm{Cr}

atoms. Finally, we characterize the light-assisted collision losses in this Bose-Fermi cold mixture.

We have constructed a magneto-optical trap for chromium atoms. Using trapping light at 425 nm and two repumping lasers tuned to intercombination transitions, over

{10}^{6}

atoms were trapped and average densities of over ${10}^{16}{\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$ were obtained. Nonexponential loss of atoms is observed at high densities indicating inelastic collisions between trapped atoms. Over a range of trapping conditions, the density-dependent trap loss rate constant \ensuremath{\beta} is extracted from fluorescence decay curves and found to have values in the range of ${10}^{\ensuremath{-}15}{\mathrm{m}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1},$ much larger than is observed in alkali-metal traps.