arXiv:1003.3867 · Physical Review A

Bose-Einstein condensation of Sr88 through sympathetic cooling with Sr87

Pascal G. Mickelson, Y. N. Martinez de Escobar, Mi Yan, B. J. DeSalvo, T. C. Killian

Published May 5, 2010• 56 citations

Abstract

We report Bose-Einstein condensation of $^{88}\mathrm{Sr}$, which has a small, negative $s$-wave scattering length (${a}_{88}=\ensuremath{-}2{a}_{0}$). We overcome the poor evaporative cooling characteristics of this isotope by sympathetic cooling with $^{87}\mathrm{Sr}$ atoms. $^{87}\mathrm{Sr}$ is effective in this role despite the fact that it is a fermion because of the large ground-state degeneracy arising from a nuclear spin of $I=9/2$, which reduces the impact of Pauli blocking of collisions. We observe a limited number of atoms in the condensate (${N}_{\mathrm{max}}\ensuremath{\approx}{10}^{4}$) that is consistent with the value of ${a}_{88}$ and the optical dipole trap parameters.

DOI: 10.1103/physreva.81.051601

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Trapping and evaporation of strontium-87 and strontium-88 mixtures

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arXiv:1003.3867 · Physical Review A

Bose-Einstein condensation of Sr88 through sympathetic cooling with Sr87

Pascal G. Mickelson, Y. N. Martinez de Escobar, Mi Yan, B. J. DeSalvo, T. C. Killian

Published May 5, 2010• 56 citations

arXiv HTML PDF

Abstract

We report Bose-Einstein condensation of

^{88}\mathrm{Sr}

, which has a small, negative

s

-wave scattering length (

{a}_{88}=\ensuremath{-}2{a}_{0}

). We overcome the poor evaporative cooling characteristics of this isotope by sympathetic cooling with

^{87}\mathrm{Sr}

atoms.

^{87}\mathrm{Sr}

is effective in this role despite the fact that it is a fermion because of the large ground-state degeneracy arising from a nuclear spin of

I=9/2

, which reduces the impact of Pauli blocking of collisions. We observe a limited number of atoms in the condensate (

{N}_{\mathrm{max}}\ensuremath{\approx}{10}^{4}

) that is consistent with the value of

{a}_{88}

and the optical dipole trap parameters.

DOI: 10.1103/physreva.81.051601

Related papers

Trapping and evaporation of strontium-87 and strontium-88 mixtures

Pascal G. Mickelson

This thesis describes trapping and evaporative cooling of ultracold 87Sr and 88Sr mixtures in an optical dipole trap to produce the first Bose-Einstein condensate (BEC) of 88Sr. Furthermore, this work presents thermalization studies that characterize the scattering properties of these ultracold strontium samples. Such ultracold atomic gases have become an important area of research because of their potential for improving optical frequency standards and for realizing quantum computation using neutral atoms. A BEC of 88Sr is particularly interesting because the small value of its background s-wave scattering length may enable the use of optical Feshbach resonances to create two-dimensional solitons. However, the small scattering length for 88Sr also hinders efficient evaporative cooling in the optical dipole trap, a necessary step to producing a BEC. Experiments with other ultracold gases have successfully overcome this hurdle by mixing in a second atomic species which, by introducing stronger interactions with the weakly interacting species, enables evaporation to colder temperatures via sympathetic cooling. For this work, we use 87Sr to sympathetically cool 88Sr during forced evaporation to quantum degeneracy.\nPrevious experiments in the Killian Lab characterized 88Sr in detail. Here, I emphasize the new or improved aspects that have allowed trapping and cooling of the mixtures of 87Sr and 88 Sr: trapping of 87Sr by itself, spectroscopic measurements of all the stable strontium isotopes to guide the trapping of isotopic mixtures, imaging of both 87Sr and 88Sr, and the various trade-offs necessary to simultaneously trap 87Sr and 88Sr. Finally, I discuss how the thermalization studies of the scattering properties of the isotopes guide the forced evaporation of mixed isotope samples. These efforts result in the production of the BEC of 88Sr, but they also point the way to future studies of fermionic quantum degeneracy in 87Sr and to the rich physics of mixed species ultracold atomic systems.This thesis describes trapping and evaporative cooling of ultracold 87Sr and 88Sr mixtures in an optical dipole trap to produce the first Bose-Einstein condensate (BEC) of 88Sr. Furthermore, this work presents thermalization studies that characterize the scattering properties of these ultracold strontium samples. Such ultracold atomic gases have become an important area of research because of their potential for improving optical frequency standards and for realizing quantum computation using neutral atoms. A BEC of 88Sr is particularly interesting because the small value of its background s-wave scattering length may enable the use of optical Feshbach resonances to create two-dimensional solitons. However, the small scattering length for 88Sr also hinders efficient evaporative cooling in the optical dipole trap, a necessary step to producing a BEC. Experiments with other ultracold gases have successfully overcome this hurdle by mixing in a second atomic species which, by introducing stronger interactions with the weakly interacting species, enables evaporation to colder temperatures via sympathetic cooling. For this work, we use 87Sr to sympathetically cool 88Sr during forced evaporation to quantum degeneracy.\nPrevious experiments in the Killian Lab characterized 88Sr in detail. Here, I emphasize the new or improved aspects that have allowed trapping and cooling of the mixtures of 87Sr and 88 Sr: trapping of 87Sr by itself, spectroscopic measurements of all the stable strontium isotopes to guide the trapping of isotopic mixtures, imaging of both 87Sr and 88Sr, and the various trade-offs necessary to simultaneously trap 87Sr and 88Sr. Finally, I discuss how the thermalization studies of the scattering properties of the isotopes guide the forced evaporation of mixed isotope samples. These efforts result in the production of the BEC of 88Sr, but they also point the way to future studies of fermionic quantum degeneracy in 87Sr and to the rich physics of mixed species ultracold atomic systems.

Jan 1, 20100 citations

Potassium scattering lengths and prospects for Bose-Einstein condensation and sympathetic cooling

Robin Côté, A. Dalgarno, H. Wang +1 more

We have determined the scattering lengths for collisions between the different isotopes of two potassium atoms in singlet and triplet molecular states of ${\mathrm{K}}_{2}$ . We show that for the two bosonic species ${}^{39}\mathrm{K}$ and ${}^{41}\mathrm{K}$ the scattering lengths are positive, hence, leading to stable condensates. The fermionic isotope ${}^{40}\mathrm{K}$ also has positive scattering lengths, but the triplet value is nearly zero, hence, a quasi-non-interacting fermionic gas. We also give results for the interspecies collisions. We conclude that double condensates of ${}^{39}\mathrm{K}$ and ${}^{41}\mathrm{K}$ are possible for purely spin-polarized atoms, and sympathetic cooling between the bosonic ${}^{39}\mathrm{K}$ and the fermionic ${}^{40}\mathrm{K}$ will be efficient due to low spin-flip rates and a sizable interspecies scattering length.We have determined the scattering lengths for collisions between the different isotopes of two potassium atoms in singlet and triplet molecular states of ${\mathrm{K}}_{2}$. We show that for the two bosonic species ${}^{39}\mathrm{K}$ and ${}^{41}\mathrm{K}$ the scattering lengths are positive, hence, leading to stable condensates. The fermionic isotope ${}^{40}\mathrm{K}$ also has positive scattering lengths, but the triplet value is nearly zero, hence, a quasi-non-interacting fermionic gas. We also give results for the interspecies collisions. We conclude that double condensates of ${}^{39}\mathrm{K}$ and ${}^{41}\mathrm{K}$ are possible for purely spin-polarized atoms, and sympathetic cooling between the bosonic ${}^{39}\mathrm{K}$ and the fermionic ${}^{40}\mathrm{K}$ will be efficient due to low spin-flip rates and a sizable interspecies scattering length.

Physical Review AJun 1, 199854 citations

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We report on the attainment of Bose-Einstein condensation of $^{86}\mathrm{Sr}$ . This isotope has a scattering length of about $+800{a}_{0}$ and thus suffers from fast three-body losses. To avoid detrimental atom loss, evaporative cooling is performed at low densities around $3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ in a large volume optical dipole trap. We obtain almost pure condensates of $5\ifmmode\times\else\texttimes\fi{}{10}^{3}$ atoms.We report on the attainment of Bose-Einstein condensation of $^{86}\mathrm{Sr}$. This isotope has a scattering length of about $+800{a}_{0}$ and thus suffers from fast three-body losses. To avoid detrimental atom loss, evaporative cooling is performed at low densities around $3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ in a large volume optical dipole trap. We obtain almost pure condensates of $5\ifmmode\times\else\texttimes\fi{}{10}^{3}$ atoms.

arXiv:1009.1701Physical Review AOct 21, 201047 citations

Bose-Einstein condensation of an ytterbium isotope

Takeshi Fukuhara, Seiji Sugawa, Yoshiro Takahashi

We report the observation of a Bose-Einstein condensate in a bosonic isotope of ytterbium $(^{170}\mathrm{Yb})$ . More than ${10}^{6}$ atoms are trapped in a crossed optical dipole trap and cooled by evaporation. Condensates of approximately ${10}^{4}$ atoms have been obtained. From an expansion of the condensate, we have extracted the scattering length ${a}_{170}=3.6\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.We report the observation of a Bose-Einstein condensate in a bosonic isotope of ytterbium $(^{170}\mathrm{Yb})$. More than ${10}^{6}$ atoms are trapped in a crossed optical dipole trap and cooled by evaporation. Condensates of approximately ${10}^{4}$ atoms have been obtained. From an expansion of the condensate, we have extracted the scattering length ${a}_{170}=3.6\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

arXiv:0709.3068Physical Review ANov 15, 2007125 citations

Production of Two Overlapping Bose-Einstein Condensates by Sympathetic Cooling

Christopher J. Myatt, Eric A. Burt, R. W. Ghrist +2 more

A new apparatus featuring a double magneto-optic trap and an Ioffe-type magnetic trap was used to create condensates of $2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms in either of the $|F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2〉$ or $|F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}1〉$ spin states of ${}^{87}$ Rb. Overlapping condensates of the two states were also created using nearly lossless sympathetic cooling of one state via thermal contact with the other evaporatively cooled state. We observed that (i) the scattering length of the $|1,\ensuremath{-}1〉$ state is positive, (ii) the rate constant for binary inelastic collisions between the two states is $2.2(9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{3}/\mathrm{s}$, and (iii) there is a repulsive interaction between the two condensates. Similarities and differences between the behaviors of the two spin states are observed.A new apparatus featuring a double magneto-optic trap and an Ioffe-type magnetic trap was used to create condensates of $2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms in either of the $|F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2〉$ or $|F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}1〉$ spin states of ${}^{87}$Rb. Overlapping condensates of the two states were also created using nearly lossless sympathetic cooling of one state via thermal contact with the other evaporatively cooled state. We observed that (i) the scattering length of the $|1,\ensuremath{-}1〉$ state is positive, (ii) the rate constant for binary inelastic collisions between the two states is $2.2(9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{3}/\mathrm{s}$, and (iii) there is a repulsive interaction between the two condensates. Similarities and differences between the behaviors of the two spin states are observed.

Physical Review LettersJan 27, 19971,225 citations

Prospects for Mixed-Isotope Bose-Einstein Condensates in Rubidium

James P. Burke, John L. Bohn, Brett D. Esry +1 more

We calculate binary collision parameters for mixtures of ultracold gases of ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ atoms. We predict a large positive triplet scattering length for mixed-isotope collisions, which implies that a stable mixed-isotope double condensate can be formed by sympathetic evaporative cooling. Moreover, collisions between ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ atoms in the lowest hyperfine manifold exhibit magnetic-field-induced Feshbach resonances which should allow partial control of the interaction between condensates. These considerations make Rb an ideal system for the study of interpenetrating bosonic superfluids.We calculate binary collision parameters for mixtures of ultracold gases of ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ atoms. We predict a large positive triplet scattering length for mixed-isotope collisions, which implies that a stable mixed-isotope double condensate can be formed by sympathetic evaporative cooling. Moreover, collisions between ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ atoms in the lowest hyperfine manifold exhibit magnetic-field-induced Feshbach resonances which should allow partial control of the interaction between condensates. These considerations make Rb an ideal system for the study of interpenetrating bosonic superfluids.

Physical Review LettersMar 9, 1998108 citations

We report Bose-Einstein condensation of

^{88}\mathrm{Sr}

, which has a small, negative

s

-wave scattering length (

{a}_{88}=\ensuremath{-}2{a}_{0}

). We overcome the poor evaporative cooling characteristics of this isotope by sympathetic cooling with

^{87}\mathrm{Sr}

atoms.

^{87}\mathrm{Sr}

is effective in this role despite the fact that it is a fermion because of the large ground-state degeneracy arising from a nuclear spin of

I=9/2

, which reduces the impact of Pauli blocking of collisions. We observe a limited number of atoms in the condensate (

{N}_{\mathrm{max}}\ensuremath{\approx}{10}^{4}

) that is consistent with the value of

{a}_{88}

and the optical dipole trap parameters.

We have determined the scattering lengths for collisions between the different isotopes of two potassium atoms in singlet and triplet molecular states of

{\mathrm{K}}_{2}

. We show that for the two bosonic species

{}^{39}\mathrm{K}

and

{}^{41}\mathrm{K}

the scattering lengths are positive, hence, leading to stable condensates. The fermionic isotope

{}^{40}\mathrm{K}

also has positive scattering lengths, but the triplet value is nearly zero, hence, a quasi-non-interacting fermionic gas. We also give results for the interspecies collisions. We conclude that double condensates of

{}^{39}\mathrm{K}

and

{}^{41}\mathrm{K}

are possible for purely spin-polarized atoms, and sympathetic cooling between the bosonic

{}^{39}\mathrm{K}

and the fermionic

{}^{40}\mathrm{K}

will be efficient due to low spin-flip rates and a sizable interspecies scattering length.

We report on the attainment of Bose-Einstein condensation of

^{86}\mathrm{Sr}

. This isotope has a scattering length of about

+800{a}_{0}

and thus suffers from fast three-body losses. To avoid detrimental atom loss, evaporative cooling is performed at low densities around $3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ in a large volume optical dipole trap. We obtain almost pure condensates of $5\ifmmode\times\else\texttimes\fi{}{10}^{3}$ atoms.

We report the observation of a Bose-Einstein condensate in a bosonic isotope of ytterbium

(^{170}\mathrm{Yb})

. More than

{10}^{6}

atoms are trapped in a crossed optical dipole trap and cooled by evaporation. Condensates of approximately

{10}^{4}

atoms have been obtained. From an expansion of the condensate, we have extracted the scattering length ${a}_{170}=3.6\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

A new apparatus featuring a double magneto-optic trap and an Ioffe-type magnetic trap was used to create condensates of $2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms in either of the

|F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2〉

or $|F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}1〉$ spin states of

{}^{87}

Rb. Overlapping condensates of the two states were also created using nearly lossless sympathetic cooling of one state via thermal contact with the other evaporatively cooled state. We observed that (i) the scattering length of the $|1,\ensuremath{-}1〉$ state is positive, (ii) the rate constant for binary inelastic collisions between the two states is $2.2(9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{3}/\mathrm{s}$, and (iii) there is a repulsive interaction between the two condensates. Similarities and differences between the behaviors of the two spin states are observed.

We calculate binary collision parameters for mixtures of ultracold gases of

{}^{85}\mathrm{Rb}

and

{}^{87}\mathrm{Rb}

atoms. We predict a large positive triplet scattering length for mixed-isotope collisions, which implies that a stable mixed-isotope double condensate can be formed by sympathetic evaporative cooling. Moreover, collisions between

{}^{85}\mathrm{Rb}

and

{}^{87}\mathrm{Rb}

atoms in the lowest hyperfine manifold exhibit magnetic-field-induced Feshbach resonances which should allow partial control of the interaction between condensates. These considerations make Rb an ideal system for the study of interpenetrating bosonic superfluids.