arXiv:0908.2071 · Physical Review Letters

Broad Feshbach Resonance in the Li6−K40 Mixture

T. G. Tiecke, M. R. Goosen, A. Ludewig, S. D. Gensemer, Stephan Kraft, S. J. J. M. F. Kokkelmans, Jook T. M. Walraven

Published Feb 3, 2010• 103 citations

Abstract

We study the widths of interspecies Feshbach resonances in a mixture of the fermionic quantum gases 6Li and 40K. We develop a model to calculate the width and position of all available Feshbach resonances for a system. Using the model, we select the optimal resonance to study the {6}Li/{40}K mixture. Experimentally, we obtain the asymmetric Fano line shape of the interspecies elastic cross section by measuring the distillation rate of 6Li atoms from a potassium-rich 6Li/{40}K mixture as a function of magnetic field. This provides us with the first experimental determination of the width of a resonance in this mixture, DeltaB=1.5(5) G. Our results offer good perspectives for the observation of universal crossover physics using this mass-imbalanced fermionic mixture.

DOI: 10.1103/physrevlett.104.053202

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arXiv:0908.2071 · Physical Review Letters

Broad Feshbach Resonance in the Li6−K40 Mixture

T. G. Tiecke, M. R. Goosen, A. Ludewig, S. D. Gensemer, Stephan Kraft, S. J. J. M. F. Kokkelmans, Jook T. M. Walraven

Published Feb 3, 2010• 103 citations

arXiv HTML PDF

Abstract

DOI: 10.1103/physrevlett.104.053202

Related papers

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We report on the experimental observation of Feshbach resonances in large-mass-imbalance mixtures of erbium (Er) and lithium (Li). All combinations of $^{168}\mathrm{Er}, ^{166}\mathrm{Er}$ , and $^{7}\mathrm{Li}, ^{6}\mathrm{Li}$ are cooled to temperatures of a few microkelvin, partially by means of sympathetic cooling together with ytterbium (Yb) as a third mixture component. The Er-Li inelastic interspecies collisional properties are studied for magnetic fields up to $680\phantom{\rule{0.28em}{0ex}}\mathrm{G}$ . In all cases, resonant interspecies loss features, indicative of Feshbach resonances, have been observed. While most resonances have sub-Gauss widths, a few of them are broad and feature widths of several Gauss. Those broad resonances are a key to the realization of ultracold Er-Li quantum gas mixtures with tunable interactions.We report on the experimental observation of Feshbach resonances in large-mass-imbalance mixtures of erbium (Er) and lithium (Li). All combinations of $^{168}\mathrm{Er}, ^{166}\mathrm{Er}$, and $^{7}\mathrm{Li}, ^{6}\mathrm{Li}$ are cooled to temperatures of a few microkelvin, partially by means of sympathetic cooling together with ytterbium (Yb) as a third mixture component. The Er-Li inelastic interspecies collisional properties are studied for magnetic fields up to $680\phantom{\rule{0.28em}{0ex}}\mathrm{G}$. In all cases, resonant interspecies loss features, indicative of Feshbach resonances, have been observed. While most resonances have sub-Gauss widths, a few of them are broad and feature widths of several Gauss. Those broad resonances are a key to the realization of ultracold Er-Li quantum gas mixtures with tunable interactions.

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^{6}\text{Li}

and

^{40}\text{K}

atoms. Our work addresses the central question of the increase in the stability of the dimers resulting from Pauli suppression of collisional losses, which is a well-known effect in mass-balanced fermionic systems near broad resonances. We present measurements of the spontaneous dissociation of dimers in dilute samples, and of the collisional losses in dense samples arising from both dimer-dimer processes and from atom-dimer processes. We find that all loss processes are suppressed close to the Feshbach resonance. Our general theoretical approach for fermionic mixtures near narrow Feshbach resonances provides predictions for the suppression of collisional decay as a function of the detuning from resonance, and we find excellent agreement with the experimental benchmarks provided by our $^{6}\text{Li}\ensuremath{-}^{40}\text{K}$ system. We finally present model calculations for other Feshbach-resonant Fermi-Fermi systems, which are of interest for experiments in the near future.

We present our experimental investigation of the interspecies Feshbach spectrum in a mixture of

{}^{167}

Er(

F = 19/2, m_F = -19/2

{}^6

Li(

F = 1/2, m_F = 1/2

) atoms in the microkelvin temperature regime. These temperatures are achieved by means of sympathetic cooling with

{}^{174}

Yb as a third species. Interspecies Feshbach resonances are then identified by investigation of the Er-Li inelastic collisional properties for magnetic fields up to 800 G. Numerous narrow resonances as well as six resonances with widths above 1 G could be identified. It is these broader resonances that hold much promise for interesting future investigations of, for exmample, novel superfluid states and Efimov states in large mass-imbalanced, all-fermionic two-component systems.

^{40}\mathrm{K}

with temperatures well below 100 nK. In particular, we locate a broad resonance at

B=389.7\phantom{\rule{0.16em}{0ex}}\text{G}

with a magnetic width of

26.7\phantom{\rule{0.28em}{0ex}}\text{G}

. Here $1\phantom{\rule{0.28em}{0ex}}\text{G}={10}^{\ensuremath{-}4}\phantom{\rule{0.16em}{0ex}}\text{T}$. Furthermore, by exciting low-energy spin waves, we demonstrate a means to precisely determine the zero crossing of the scattering length for this broad Feshbach resonance. Our findings allow for further tunability in experiments with ultracold

^{40}\mathrm{K}

quantum gases.

We report on the experimental observation of Feshbach resonances in large-mass-imbalance mixtures of erbium (Er) and lithium (Li). All combinations of

^{168}\mathrm{Er}, ^{166}\mathrm{Er}

, and

^{7}\mathrm{Li}, ^{6}\mathrm{Li}

are cooled to temperatures of a few microkelvin, partially by means of sympathetic cooling together with ytterbium (Yb) as a third mixture component. The Er-Li inelastic interspecies collisional properties are studied for magnetic fields up to

680\phantom{\rule{0.28em}{0ex}}\mathrm{G}

. In all cases, resonant interspecies loss features, indicative of Feshbach resonances, have been observed. While most resonances have sub-Gauss widths, a few of them are broad and feature widths of several Gauss. Those broad resonances are a key to the realization of ultracold Er-Li quantum gas mixtures with tunable interactions.