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Physical Review A

Measurement of the three-body-recombination coefficient of ultracold lithium and strontium atoms

Boyang Wang, Yifan Wang, Zi-He An, Li-Yang Xie, Zhu-Xiong Ye, Yi Zhang, Meng Khoon Tey

Published Jul 25, 2024• 1 citation
Publisher

Abstract

We report on the observation of a conspicuous loss in an ultracold mixture of $^{7}\mathrm{Li}$ and $^{88}\mathrm{Sr}$ atoms confined in a far-off-resonance optical dipole trap. We attribute the trap loss to the three-body inelastic Li-Sr-Sr collision and extract the corresponding three-body-recombination coefficient ${K}_{3}$ at $T\ensuremath{\sim}18.5,45,70,600\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}$. The measured three-body-recombination coefficient is about two to three orders of magnitude larger than the typical values convenient for realizing quantum degenerate gases, and essentially rules out the prospect of realizing $^{7}\mathrm{Li}$ and $^{88}\mathrm{Sr}$ mixtures of high phase space density. The measured three-body-recombination rates agree with the unitarity limit at high temperatures. Our results also confirm that the three-body-recombination loss is dominated by the light-heavy-heavy process, in agreement with the prediction for a system with a large mass-imbalanced and negligible intraspecies interaction.

DOI
10.1103/physreva.110.013322

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We report on the observation of a conspicuous loss in an ultracold mixture of 7Li^{7}\mathrm{Li}7Li and 88Sr^{88}\mathrm{Sr}88Sr atoms confined in a far-off-resonance optical dipole trap. We attribute the trap loss to the three-body inelastic Li-Sr-Sr collision and extract the corresponding three-body-recombination coefficient K3{K}_{3}K3​ at T\ensuremath∼18.5,45,70,600\textmuKT\ensuremath{\sim}18.5,45,70,600\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}T\ensuremath∼18.5,45,70,600\textmuK. The measured three-body-recombination coefficient is about two to three orders of magnitude larger than the typical values convenient for realizing quantum degenerate gases, and essentially rules out the prospect of realizing 7Li^{7}\mathrm{Li}7Li and 88Sr^{88}\mathrm{Sr}88Sr mixtures of high phase space density. The measured three-body-recombination rates agree with the unitarity limit at high temperatures. Our results also confirm that the three-body-recombination loss is dominated by the light-heavy-heavy process, in agreement with the prediction for a system with a large mass-imbalanced and negligible intraspecies interaction.
We report on the observation of a conspicuous loss in an ultracold mixture of 7^{7}7Li and 88^{88}88Sr atoms confined in a far-off-resonance optical dipole trap. We attribute the trap loss to the three-body inelastic Li-Sr-Sr collision and extract the corresponding three-body recombination coefficient K3K_3K3​ at T∼18.5,45,70,600T\sim 18.5,45,70,600T∼18.5,45,70,600 μKμKμK. The measured three-body recombination coefficient is about two to three orders of magnitude larger than the typical values convenient for realizing quantum degenerate gases. It also indicates a potentially large sss-wave scattering length between the bosonic 7^{7}7Li and 88^{88}88Sr atoms, and essentially rules out the prospect of realizing 7^77Li and 88^{88}88Sr mixtures of high phase space density.
We study Efimov resonances via three-body loss in an ultracold two-component gas of fermionic 6Li^{6}\mathrm{Li}6Li and bosonic 133Cs^{133}\mathrm{Cs}133Cs atoms close to a Feshbach resonance at 843 G, extending results reported previously [Pires et al., Phys. Rev. Lett. 112, 250404 (2014)] to temperatures around 120 nK. The experimental scheme for reaching lower temperatures is based upon compensating the gravity-induced spatial separation of the mass-imbalanced gases with bichromatic optical dipole traps. We observe the first and second excited Li-Cs-Cs Efimov resonance in the magnetic field dependence of the three-body event rate constant, in good agreement with the universal zero-range theory at finite temperature [Petrov and Werner, Phys. Rev. A 92, 022704 (2015)]. Deviations are found for the Efimov ground state, and the inelasticity parameter $\ensuremath{\eta}$ is found to be significantly larger than those for single-species systems.
Ultracold gases have become versatile systems to study quantum many-body effects. Their high degree of control and the tunability of the atomic interactions led to important advances in the understanding of strongly correlated matter. In the regime of strong interactions, unlike fermions, the study of bosons is hampered by three-particle recombination that leads to atom losses and keeps the system from reaching a real equilibrium state. In this thesis, we have performed the first quantitative comparison between theory and experiment on the three-particle loss coefficient L_3(a,T), for arbitrary scattering length a and temperature T. For unitary two-particle scattering (|a| → ∞), we show that the three-particle loss coefficient follows the law L_3(∞, T ) = λ_3/T^2, that we have tested using a trapped non-degenerate ^{7}Li gas maintained at constant temperature. The measured value of λ_3 = 2.5(3)_{stat}(6)_{cyst} × 10^{−20}(μK)^2cm^6s^{−1} is, within the error bars in good agreement with the theory prediction λ_3^{th} = 1.52 × 10^{−20}(μK)^2cm^6s^{−1}. We have extended our measurements to arbitrary values of the scattering length a. For a < 0, the theory predicts a smooth connection between the previously derived zero-temperature model for L_3(a, 0) and the unitarity limited loss coefficient L_3(∞, T ). We also show that a second Efimov resonance in 7Li should be observable near a = − 500 a0 for a temperature of 1 μK. Finally, we compare our theoretical prediction with measurements performed at Innsbruck with ^{133}Cs and at Cambridge with ^{39}K. The theory also shows remarkable quantitative agreement with these measurements.
Within the universal zero-range theory, we compute the three-body recombination rate to deep molecular states for two identical bosons resonantly interacting with each other and with a third atom of another species, in the absence of weakly bound dimers. The results allow for a quantitative understanding of loss resonances at finite temperature and, combined with experimental data, can be used for testing the Efimov universality and extracting the corresponding three-body parameters in a given system. Curiously, we find that the loss rate can be dramatically enhanced by the resonant heavy-heavy interaction, even for high mass ratios where this interaction is practically irrelevant for the Efimov scaling factor. This effect is important for analyzing the recent loss measurements in the Cs-Li mixture.
We report on the observation of two Feshbach resonances in collisions between ultracold 6Li^{6}\mathrm{Li}6Li and 87Rb^{87}\mathrm{Rb}87Rb atoms in their respective hyperfine ground states $\ensuremath{\mid}F,{m}_{F}⟩=\ensuremath{\mid}1∕2,1∕2⟩$ and \ensuremath{\mid}1,1⟩. The resonances show up as trap losses for the 6Li^{6}\mathrm{Li}6Li cloud induced by inelastic Li-Rb-Rb three-body collisions. The magnetic field values where they occur represent important benchmarks for an accurate determination of the interspecies interaction potentials. A broad Feshbach resonance located at 1066.92G1066.92\phantom{\rule{0.3em}{0ex}}\mathrm{G}1066.92G opens interesting prospects for the creation of ultracold heteronuclear molecules. We furthermore observe a strong enhancement of the narrow ppp-wave Feshbach resonance in collisions of 6Li^{6}\mathrm{Li}6Li atoms at 158.55G158.55\phantom{\rule{0.3em}{0ex}}\mathrm{G}158.55G in the presence of a dense 87Rb^{87}\mathrm{Rb}87Rb cloud. The effect of the 87Rb^{87}\mathrm{Rb}87Rb cloud is to introduce Li-Li-Rb three-body collisions occurring at a higher rate than Li-Li-Li collisions.
We study three-body recombination in an ultracold Bose-Fermi mixture. We first show theoretically that, for weak interspecies coupling, the loss rate is proportional to Tan's contact. Second, using a ^{7}Li/^{6}Li mixture we probe the recombination rate in both the thermal and dual superfluid regimes. We find excellent agreement with our model in the BEC-BCS crossover. At unitarity where the fermion-fermion scattering length diverges, we show that the loss rate is proportional to n_{f}^{4/3}, where n_{f} is the fermionic density. This unusual exponent signals nontrivial two-body correlations in the system. Our results demonstrate that few-body losses can be used as a quantitative probe of quantum correlations in many-body ensembles.