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Dynamics of a degenerate Cs-Yb mixture with attractive interspecies interactions

KE Wilson, A Guttridge, I-Kang Liu, JP Segal, T. P. Billam, Nicholas G. Parker, Nick P. Proukakis, SL Cornish

Published Jul 27, 2021• 0 citations
Publisher

Abstract

We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of 133Cs and 174Yb with attractive interspecies interactions. Specifically, we excite vertical center-of-mass oscillations of the Cs condensate. We observe significant damping for the Cs dipole mode, due to the rapid transfer of energy to the larger Yb component and the ensuing acoustic dissipation. Numerical simulations based on coupled Gross-Pitaevskii equations provide excellent agreement with experiment and additionally reveal the possibility of late-time revivals (beating), which are found to be highly sensitive to the Cs and Yb atom number combinations. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture. We observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction when aCs<50a0, well above the single-species collapse threshold, in good agreement with simulations.

DOI
10.25405/ncl.34430244

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We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of 133Cs and 174Yb with attractive interspecies interactions. Specifically, we excite vertical center-of-mass oscillations of the Cs condensate. We observe significant damping for the Cs dipole mode, due to the rapid transfer of energy to the larger Yb component and the ensuing acoustic dissipation. Numerical simulations based on coupled Gross-Pitaevskii equations provide excellent agreement with experiment and additionally reveal the possibility of late-time revivals (beating), which are found to be highly sensitive to the Cs and Yb atom number combinations. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture. We observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction when aCs<50a0, well above the single-species collapse threshold, in good agreement with simulations.
We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of 133Cs^{133}\mathrm{Cs}133Cs and 174Yb^{174}\mathrm{Yb}174Yb with attractive interspecies interactions. Specifically, we excite vertical center-of-mass oscillations of the Cs condensate. We observe significant damping for the Cs dipole mode, due to the rapid transfer of energy to the larger Yb component and the ensuing acoustic dissipation. Numerical simulations based on coupled Gross-Pitaevskii equations provide excellent agreement with experiment and additionally reveal the possibility of late-time revivals (beating), which are found to be highly sensitive to the Cs and Yb atom number combinations. By further tuning the interaction strength of Cs using a broad Feshbach resonance, we explore the stability of the degenerate mixture. We observe collapse of the Cs condensate mediated by the attractive Cs-Yb interaction when aCs<50a0{a}_{\mathrm{Cs}}<50\phantom{\rule{0.28em}{0ex}}{a}_{0}aCs​<50a0​, well above the single-species collapse threshold, in good agreement with simulations.
We report the production of quantum degenerate Bose-Bose mixtures of Cs and Yb with both attractive (Cs + 174Yb) and repulsive (Cs + 170Yb) interspecies interactions. Dual-species evaporation is performed in a bichromatic optical dipole trap that combines light at 1070 nm and 532 nm to enable control of the relative trap depths for Cs and Yb. Maintaining a trap which is shallower for Yb throughout the evaporation leads to highly efficient sympathetic cooling of Cs for both isotopic combinations at magnetic fields close to the Efimov minimum in the Cs three-body recombination rate at around 22 G. For Cs + 174Yb, we produce quantum mixtures with typical atom numbers of NYb ∼ 5 × 104 and NCs ∼ 5 × 103. We find that the attractive interspecies interaction (characterized by the scattering length aCsYb = −75a0) is stabilized by the repulsive intraspecies interactions. For Cs + 170Yb, we produce quantum mixtures with typical atom numbers of NYb ∼ 4 × 104 and NCs ∼ 1 × 104. Here, the repulsive interspecies interaction (aCsYb = 96a0) can overwhelm the intraspecies interactions, such that the mixture sits in a region of partial miscibility
We unravel the coupled dipole dynamics of a two-species Bose-Einstein condensate with tunable interspecies interaction. We produce a degenerate mixture of $^{41}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ in an optical trap and we study the dipole oscillations of both atomic species in the linear response regime. Varying the interspecies interaction from the weakly to the strongly attractive side, we measure the frequencies and the composition of the two dipole eigenmodes. For sufficiently strong interactions, even beyond the mean-field collapse, we find that the frequency of the low-energy eigenmode is determined only by the bare trap frequencies and the species population imbalance. The experimental results are well reproduced by numerical simulations based on two coupled Gross-Pitaevskii equations. Our findings provide a detailed picture of the dipole excitations in asymmetric bosonic mixtures.
We report on the formation of a stable quantum degenerate mixture of fermionic ^{6}Li and bosonic ^{133}Cs in an optical trap by sympathetic cooling near an interspecies Feshbach resonance. New regimes of quantum degenerate Bose-Fermi mixtures are identified. With moderate attractive interspecies interactions, we show that a degenerate Fermi gas of Li can be fully confined in a Cs Bose-Einstein condensate without external potentials. For stronger attraction where mean-field collapse is expected, no such instability is observed. Potential mechanisms to explain this phenomenon are discussed.
In this paper, we present a theoretical study of a two-component Bose-Einstein condensate composed of ytterbium (Yb) isotopes in a three-dimensional anisotropic harmonic potential. The condensate consists of a mixture of 176Yb^{176}\mathrm{Yb}176Yb atoms which have a negative sss-wave scattering length and 174Yb^{174}\mathrm{Yb}174Yb atoms having a positive sss-wave scattering length. We study the ground-state as well as dynamic properties of this two-component condensate. Due to the attractive interactions between 176Yb^{176}\mathrm{Yb}176Yb atoms, the condensate of 176Yb^{176}\mathrm{Yb}176Yb undergoes a collapse when the particle number exceeds a critical value. The critical number and the collapse dynamics are modified due to the presence of 174Yb^{174}\mathrm{Yb}174Yb atoms. We use coupled two-component Gross-Pitaevskii equations to study the collapse dynamics. The theoretical results obtained are in reasonable agreement with the experimental results of Fukuhara et al. [Phys. Rev. A 79, 021601(R) (2009)].
This thesis reports the formation of a dual-species Bose-Einstein condensate of 87^{87}87Rb and 133^{133}133Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation. The experimental method exploits the efficient sympathetic cooling of 133^{133}133Cs via elastic collisions with 87^{87}87Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate \mbox{∼10−25−10−26\sim10^{-25}-10^{-26}∼10−25−10−26~cm6/^{6}/6/s}. The two condensates each contain up to \mbox{2×1042\times10^{4}2×104} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the 87^{87}87Rb during the cooling leads to the creation of single-species 133^{133}133Cs condensates of up to \mbox{6×1046\times10^{4}6×104} atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)~G and the creation of a pure sample of Cs2_{2}2​ molecules via magneto-association on the 4(g)4 resonance at 19.8~G. These results represent important steps towards the creation of ultracold polar RbCs molecules.