Physical Review Letters

Prospects for Mixed-Isotope Bose-Einstein Condensates in Rubidium

James P. Burke, John L. Bohn, Brett D. Esry, Chris H. Greene

Published Mar 9, 1998• 108 citations

Abstract

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.

DOI: 10.1103/physrevlett.80.2097

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Physical Review Letters

Prospects for Mixed-Isotope Bose-Einstein Condensates in Rubidium

James P. Burke, John L. Bohn, Brett D. Esry, Chris H. Greene

Published Mar 9, 1998• 108 citations

Publisher

Abstract

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.

DOI: 10.1103/physrevlett.80.2097

Related papers

Collisional Properties of Ultracold K-Rb Mixtures

G. Ferrari, M. Inguscio, W. Jastrzȩbski +3 more

We determine the interspecies $s$ -wave triplet scattering length ${a}_{3}$ for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between $^{\mathrm{41}}\mathrm{K}$ and $^{87}\mathrm{R}\mathrm{b}$ in different temperature regimes. The positive value ${a}_{3}=+{163}_{\ensuremath{-}12}^{+57}{a}_{0}$ ensures the stability against collapse of binary $^{41}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensates. For the fermion-boson mixture $^{40}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.We determine the interspecies $s$-wave triplet scattering length ${a}_{3}$ for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between $^{\mathrm{41}}\mathrm{K}$ and $^{87}\mathrm{R}\mathrm{b}$ in different temperature regimes. The positive value ${a}_{3}=+{163}_{\ensuremath{-}12}^{+57}{a}_{0}$ ensures the stability against collapse of binary $^{41}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensates. For the fermion-boson mixture $^{40}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.

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A $^{23}$ Na and $^{87}$ Rb double Bose-Einstein condensate with tunable interactionsA $^{23}$Na and $^{87}$Rb double Bose-Einstein condensate with tunable interactions

Dezhi Xiong, Xiaoke Li, Fudong Wang +1 more

We have realized a dual-species Bose-Einstein condensate of $^{23}$ Na and $^{87}$ Rb atoms and observed their immiscibility. Because of the favorite background intra- and inter-species scattering lengths, evaporative cooling and sympathetic cooling are efficient without the need for fine controlling of the interactions. Our system thus provides a clean platform for studying quantum fluid mixtures with tunable inter-species interactions. We have also demonstrated the interaction tuning with a inter-species Feshbach resonance by investigating the elastic collisions near zero crossing of the Na-Rb scattering length.We have realized a dual-species Bose-Einstein condensate of $^{23}$Na and $^{87}$Rb atoms and observed their immiscibility. Because of the favorite background intra- and inter-species scattering lengths, evaporative cooling and sympathetic cooling are efficient without the need for fine controlling of the interactions. Our system thus provides a clean platform for studying quantum fluid mixtures with tunable inter-species interactions. We have also demonstrated the interaction tuning with a inter-species Feshbach resonance by investigating the elastic collisions near zero crossing of the Na-Rb scattering length.

May 30, 20135 citations

We calculate binary collision parameters for mixtures of ultracold gases of

{}^{85}\mathrm{Rb}

and

{}^{87}\mathrm{Rb}

{}^{85}\mathrm{Rb}

and

{}^{87}\mathrm{Rb}

We determine the interspecies

s

-wave triplet scattering length

{a}_{3}

for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between

^{\mathrm{41}}\mathrm{K}

and

^{87}\mathrm{R}\mathrm{b}

in different temperature regimes. The positive value ${a}_{3}=+{163}_{\ensuremath{-}12}^{+57}{a}_{0}$ ensures the stability against collapse of binary $^{41}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensates. For the fermion-boson mixture $^{40}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.

{}^{39}\mathrm{K}

triplet scattering length will hamper efforts to produce a Bose-Einstein condensate, unless experiments utilize a broad, accessible magnetic Feshbach resonance. The large positive value calculated for the

{}^{41}\mathrm{K}

triplet scattering length makes it a better candidate for condensation at zero magnetic field. The fermionic isotope

{}^{40}\mathrm{K}

is also predicted to have a large, positive scattering length for elastic collisions between spin states of experimental interest, implying that it can be efficiently evaporatively cooled to the quantum degenerate regime. In addition, certain spin states possess Feshbach resonances that may enable tuning of its interatomic interactions, possibly leading to the formation of Cooper pairs.

We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic

^{40}\mathrm{K}

and bosonic

^{87}\mathrm{Rb}

atoms. The magnetic-field locations of 13 interspecies resonances are used to construct a quantum collision model able to predict accurate collisional parameters for all $\mathrm{K}\text{\ensuremath{-}}\mathrm{Rb}$ isotopic pairs. In particular, we determine the interspecies

s

-wave singlet and triplet scattering lengths for the $^{40}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ mixture as $(\ensuremath{-}108\ifmmode\pm\else\textpm\fi{}3){a}_{0}$ and $(\ensuremath{-}205\ifmmode\pm\else\textpm\fi{}5){a}_{0}$, respectively. We also predict accurate scattering lengths and the position of Feshbach resonances for the other $\mathrm{K}\text{\ensuremath{-}}\mathrm{Rb}$ isotopic pairs. We discuss the consequences of our results for current and future experiments with ultracold $\mathrm{K}\text{\ensuremath{-}}\mathrm{Rb}$ mixtures.

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.

On the basis of recently measured

{\mathrm{Rb}}_{2}

bound-state energies and continuum properties, we predict magnetically induced Feshbach resonances in collisions of ultracold rubidium atoms. The resonances make it possible to control the sign and magnitude of the effective particle-particle interaction in a Rb Bose-Einstein condensate by tuning a bias magnetic field. For the case of

{}^{85}\mathrm{Rb}

they occur at field values in the range where these atoms can be magnetostatically trapped. For

{}^{87}\mathrm{Rb}

they are predicted to occur at negative field values.

^{23}

Na and

^{87}

Rb double Bose-Einstein condensate with tunable interactions

We have realized a dual-species Bose-Einstein condensate of

^{23}

Na and

^{87}

Rb atoms and observed their immiscibility. Because of the favorite background intra- and inter-species scattering lengths, evaporative cooling and sympathetic cooling are efficient without the need for fine controlling of the interactions. Our system thus provides a clean platform for studying quantum fluid mixtures with tunable inter-species interactions. We have also demonstrated the interaction tuning with a inter-species Feshbach resonance by investigating the elastic collisions near zero crossing of the Na-Rb scattering length.