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arXiv:1911.06538 · Journal of Physics Conference Series

Ultracold collisions in the Yb-Li mixture system

Florian Schäfer, Hideki Konishi, Adrien Bouscal, Tomoya Yagami, Matthew D Frye, Jeremy M Hutson, Yoshiro Takahashi

Published Jan 1, 2020• 1 citation
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Abstract

We report our experimental results on the collisional physics between non-S-state atoms (ytterbium (Yb), effectively a two-electron system, in the metastable 3 P 2 state) and S-state atoms (lithium (Li), an alkali metal, in the ground state). At low magnetic fields, by measuring inelastic interspecies collisional losses in the double quantum degenerate mixture we reveal the strong dependence of the inelastic losses on the internal spin states of both species and suppressed losses in stretched state configurations. Increasing the magnetic field up to 800 G we further investigate the magnetic field dependence of the collisional interactions. There, smoothly increasing inelastic losses are observed towards higher fields. The combined knowledge of both the magnetic field and the spin state dependence of the collisional losses of this prototypical mixture system of non-S-state and S-state atoms provides a significant step forward towards controllable impurity physics realized in the Yb-Li ultracold system.

DOI
10.1088/1742-6596/1412/6/062005

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•Sep 5, 2016•0 citations
We report our experimental results on the collisional physics between non-S-state atoms (ytterbium (Yb), effectively a two-electron system, in the metastable 3 P 2 state) and S-state atoms (lithium (Li), an alkali metal, in the ground state). At low magnetic fields, by measuring inelastic interspecies collisional losses in the double quantum degenerate mixture we reveal the strong dependence of the inelastic losses on the internal spin states of both species and suppressed losses in stretched state configurations. Increasing the magnetic field up to 800 G we further investigate the magnetic field dependence of the collisional interactions. There, smoothly increasing inelastic losses are observed towards higher fields. The combined knowledge of both the magnetic field and the spin state dependence of the collisional losses of this prototypical mixture system of non-S-state and S-state atoms provides a significant step forward towards controllable impurity physics realized in the Yb-Li ultracold system.
Experimentally the spin dependence of inelastic collisions between ytterbium (Yb) in the metastable state and lithium (Li) in the ground state manifold is investigated at low magnetic fields. Using selective excitation all magnetic sublevels m J of Yb( ) are accessed and four of the six lowest lying magnetic sublevels of are prepared by optical pumping. On the one hand, m J -independence of collisions involving Li( ) atoms is found. A systematic m J -dependence in collisions with Li( ) atoms, in particular suppressed losses for stretched collisional states, is observed on the other hand. Further, m J -changing processes are found to be of minor relevance. The span of observed inelastic collision rates is between and , and a possible origin of the observed behavior is discussed.
We present experimental results on the inelastic and elastic interspecies interactions between ytterbium (Yb) in the metastable 3P2{}^{3}P{}_{2}3P2​ state loaded into a deep optical lattice and spin polarized lithium (Li) in its ground state. Focusing on the mJ=0{m}_{J}=0mJ​=0 magnetic sublevel of Yb(3P2\mathrm{Yb}({}^{3}P{}_{2}Yb(3P2​), bias magnetic fields between 20 and 800G800\phantom{\rule{0.28em}{0ex}}\mathrm{G}800G are investigated and significantly enhanced inelastic collision rates with high magnetic fields are found. In addition, by direct spectroscopy of the Yb Mott insulator immersed in the Li Fermi gas an upper boundary of the background scattering length of the $\mathrm{Yb}({}^{3}P{}_{2},{m}_{J}=0)\ensuremath{-}\mathrm{Li}{(}^{2}{S}_{1/2},F=1/2,{m}_{F}=+1/2$) system is estimated, revealing the absence of useful Feshbach resonances. These observations are qualitatively consistent with the theoretical calculations.
We establish an experimental method for a detailed investigation of inelastic collisional properties between ytterbium (Yb) in the metastable state and ground state lithium (Li). By combining an optical lattice and a direct excitation to the state we achieve high selectivity on the collisional partners. Using this method we determine inelastic loss coefficients in collisions between 174 Yb( ) with magnetic sublevels of m J = 0 and −2 and ground state 6 Li to be and , respectively. Absence of spin changing processes in Yb( )–Li inelastic collisions at low magnetic fields is confirmed by inelastic loss measurements on the m J = 0 state. We also demonstrate that our method allows us to look into loss processes in few-body systems separately.
Spin-polarized metastable atoms of ultracold ytterbium are trapped at high density and their inelastic collisional properties are measured. We reveal that in collisions of Yb(3P2{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{2}3P2​) with Yb(1S0{}^{1}\phantom{\rule{-0.16em}{0ex}}{S}_{0}1S0​) there is relatively weak inelastic loss, but with a significant spin dependence consistent with Zeeman sublevel changes as being the dominant decay process. This is in strong contrast to our observations of Yb(3P2{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{2}3P2​)--Yb(3P2{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{2}3P2​) collisional losses, which are, at low field, much more rapid and have essentially no spin dependence. Our results give a guideline to using the 3P2{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{2}3P2​ states in many possible applications.
We report on the realization of an ultracold mixture of lithium atoms in the ground state and ytterbium atoms in an excited metastable (3P2) state. Such a mixture can support broad magnetic Feshbach resonances which may be utilized for the production of ultracold molecules with an electronic spin degree of freedom, as well as novel Efimov trimers. We investigate the interaction properties of the mixture in the presence of an external magnetic field and find an upper limit for the background interspecies two-body inelastic decay coefficient of K2'<3×10(-12) cm3/s for the 3P2 mJ=-1 substate. We calculate the dynamic polarizabilities of the Yb(3P2) magnetic substates for a range of wavelengths, and find good agreement with our measurements at 1064 nm. Our calculations also allow the identification of magic frequencies where Yb ground and metastable states are identically trapped and the determination of the interspecies van der Waals coefficients.
In an ultracold, optically trapped mixture of 87^{87}87Rb and metastable triplet 4^44He atoms we have studied trap loss for different spin-state combinations, for which interspecies Penning ionization is the main two-body loss process. We observe long trapping lifetimes for the purely quartet spin-state combination, indicating strong suppression of Penning ionization loss by at least two orders of magnitude. For the other spin-mixtures we observe short lifetimes that depend linearly on the doublet character of the entrance channel. We compare the extracted loss rate coefficient with recent predictions of multichannel quantum-defect theory for reactive collisions involving a strong exothermic loss channel and find near-universal loss for doublet scattering. Our work demonstrates control of reactive collisions by internal atomic state preparation, which also implies magnetic field tunability.