Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session N6: Bose-Fermi Mixtures |
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Chair: Christophe Salomon, ENS, Paris Room: 311-312 |
Thursday, June 8, 2017 10:30AM - 10:42AM |
N6.00001: One, two, three, many: few body losses in many-body ensembles Frederic Chevy, Sebastien Laurent, Matthieu Pierce, Tarik Yefsah, Christophe Salomon Recent experiments have demonstrated the possibility of achieving dual superfluidity in Bose-Fermi mixtures. In my talk I will address the remakable stability of these systems and show that in weakly-coupled mixtures, the loss rate is proportional to Tan's contact parameter that quantifies the short-range behaviour of two-body correlations in the fermionic system. 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 the $4/3$ power of the fermionic density. Our result interpolate between the three-body losses expected in the weakly attractive (BCS) limit and the dominant two-body dimer-dimer processes in the strongly attractive (BEC) regime. [Preview Abstract] |
Thursday, June 8, 2017 10:42AM - 10:54AM |
N6.00002: Two-Element Mixture of Bose and Fermi Superfluids Richard Roy, Alaina Green, Ryan Bowler, Subhadeep Gupta We report on the production of a stable mixture of bosonic and fermionic superfluids composed of the elements $^{174}$Yb and $^6$Li which feature a strong mismatch in mass and distinct electronic properties. We demonstrate elastic coupling between the superfluids by observing the shift in dipole oscillation frequency of the bosonic component due to the presence of the fermions. The measured magnitude of the shift is consistent with a mean-field model and its direction determines the previously unknown sign of the interspecies scattering length to be positive. We also observe the exchange of angular momentum between the superfluids from the excitation of a scissors mode in the bosonic component through interspecies interactions. We explain this observation using an analytical model based on superfluid hydrodynamics. [Preview Abstract] |
Thursday, June 8, 2017 10:54AM - 11:06AM |
N6.00003: Collective modes of a BEC immersed in a Fermi sea Bo Huang, Rianne S. Lous, Isabella Fritsche, Fabian Lehmann, Michael Jag, Emil Kirilov, Rudolf Grimm, Mikhail A. Baranov The collective dynamics of a trapped Bose-Einstein condensation(BEC) can change significantly when the BEC is strongly interacting with a degenerate Fermi gas. We realize such a quantum mixture with a $^{41}$K BEC immersed in a large single-component degenerate Fermi gas of $^6$Li, and both elements are trapped in an elongated optical dipole trap while the interspecies contact interaction is manipulated by a magnetic Feshbach resonance between the lowest spin state of both elements near 335.08 G. When the interspecies repulsive interaction increases, the two components start to repel each other, i.e. the BEC density is enhanced while the fermions are depleted at the trap center, and finally become spatially separated when the interaction is sufficiently strong. Across this transition, we measure the frequencies of BEC collective oscillations and observe a substantial change of the frequency of the radial breathing mode. We interpret our observations with a mean-field model beyond the local-density approximation. [Preview Abstract] |
Thursday, June 8, 2017 11:06AM - 11:18AM |
N6.00004: Phase Separation in a Fermi-Bose Mixture of $^6$Li and $^{41}$K Rianne S. Lous, Bo Huang, Isabella Fritsche, Fabian Lehmann, Michael Jag, Emil Kirilov, Rudolf Grimm We report on the observation of phase separation between a $^{41}$K Bose-Einstein condensate (BEC) and a $^{6}$Li Fermi sea with strong repulsive interspecies interactions. After evaporation in an optical dipole trap, we obtain a BEC of $10^4$ $^{41}$K atoms and a Fermi sea of $10^5$ $^{6}$Li atoms with $T/T_F< 0.07$. We explore this double-degenerate mixture by tuning the heternonuclear interaction with the help of a Feshbach resonance at $335.08\,$G. We use three-body recombination as a probe to study the overlap between the two species for various interaction strengths. We see a decrease in losses when the interactions become strongly repulsive and compare the loss rate to that of a non-condensed bosonic cloud. In a phase-separated mixture, losses only happen at the interface of the two species and are therefore reduced, when compared to a mixed phase of both species. To understand our loss rate results, we calculate the spatial overlap between the two components with a mean-field model. This model fits nicely to our experimental results and reveals effects beyond the local density approximation (LDA). [Preview Abstract] |
Thursday, June 8, 2017 11:18AM - 11:30AM |
N6.00005: Dual-Degeneracy in a Bose-Fermi Mixture with Extreme Mass Imbalance B. J. DeSalvo, Krutik Patel, Jacob Johansen, Cheng Chin We have produced the first quantum degenerate mixture of bosonic $^{133}$Cs and fermionic $^6$Li. Owing to a narrow Feshbach resonance at 892 G, this system offers a flexible platform in which to study strongly interacting Bose-Fermi mixtures with large mass imbalance. To produce this sample, we first sequentially laser cool and load each species into separate optical dipole traps. The two species are evaporatively cooled and then combined at $\sim 200$ nK in a dual-color optical dipole trap. After a final stage of evaporative cooling near an interspecies Feshbach resonance, we obtain nearly pure Bose-Einstein condensates of $ \sim 2 \times 10^4$ Cs atoms and $T/T_F \sim 0.2$ for Li. By tuning the interspecies interactions via the Feshbach resonance, we explore the phase diagram of this system and will present our efforts to observe beyond mean-field effects. [Preview Abstract] |
Thursday, June 8, 2017 11:30AM - 11:42AM |
N6.00006: Testing universality of Efimov Physics based on a mass-imbalanced Li-Cs mixture Jacob Johansen, Brian DeSalvo, Krutik Patel, Cheng Chin Efimov states are notable for their universal geometric scaling and are observable in ultracold atomic systems employing magnetic Feshbach resonances. In addition to geometric scaling, which we observed previously by taking advantage of a reduced Efimov scaling constant in our mass imbalanced $^6$Li-$^{133}$Cs system, an interesting pattern has emerged in Efimov measurements: while expected to be non-universal, the absolute positions of Efimov resonances appear to scale simply with van der Waals length. Theories attempting to explain this observation have predicted a dependence on the strength of the Feshbach resonance for narrow resonances, yet experiments attempting to probe this regime have so far been inconsistent with the predicted dependence. In this talk, we focus primarily on our recent measurements showing dependence on Feshbach resonance strength. We directly compare two Feshbach resonances, one broad and one very narrow, which are nearly identical with the exception of the resonance strength, and find a striking difference in the first Efimov resonance position. Our measurement makes significant strides toward resolving the discrepancy between experiment and theory which exists in the field today. [Preview Abstract] |
Thursday, June 8, 2017 11:42AM - 11:54AM |
N6.00007: Thermodynamics and Structural Transition of Binary Fermi-Bose Mixtures of Ultracold Atoms Tom Kim, Chih-Chun Chien A mixture of spin-polarized fermionic and repulsive bosonic ultracold atoms can go through phase separation if the boson-fermion interaction is sufficiently large and the temperature sufficiently low. By evaluating the grand partition function from standard statistical mechanics, we obtain the thermodynamic free energies and its associated quantities at finite temperatures. We examine the stability of a mixture from the structure of the free energy. For a uniform box potential, strong interspecies repulsion separates the two components, and the thermodynamic quantities of each component can be systematically determined. A mixture in a harmonic trap distorts the density profiles. By using the local density approximation, we found several different structures, such as partially mixed regions or fully separated regions, depending on the mass ratio and interactions. [Preview Abstract] |
Thursday, June 8, 2017 11:54AM - 12:06PM |
N6.00008: Toward Creation of Triplet Ground State NaLi Molecules Hyungmok Son, Timur Rvachov, Ariel Sommer, Juliana Park, Sepehr Ebadi, Martin Zwierlein, Wolfgang Ketterle, Alan Jamison Ultracold heteronuclear molecules offer a unique platform for the study of many-body physics, quantum information processing, and controlled chemistry at the quantum level. For this purpose, diatomic molecules in absolute, singlet ground states have been created with various combinations of alkali atoms. The NaLi molecules is unique in that the triplet ground state is expected to have a long collisional lifetime, giving access to novel spin lattice Hamiltonians that harness with both the electric and magnetic moments. In addition, as the lightest bialkali dimer, the low density of states will provide us with the potential to study resolved Feshbach resonances between the molecules. We report our progress on the creation of a large sample of fermionic NaLi molecules in the triplet ground state through STIRAP from weakly-bound molecules, which may be produced through magneto-association or two-stage photo-association. [Preview Abstract] |
Thursday, June 8, 2017 12:06PM - 12:18PM |
N6.00009: Photoassociation spectroscopy of heteronuclear LiYb molecules Alaina Green, Richard Roy, Ryan Bowler, Subhadeep Gupta We probe the electronically excited potentials of Li*Yb with photoassociation (PA) spectroscopy in a dual-species optical dipole trap. Previous studies of interspecies PA by trap-loss spectroscopy in a double MOT were hindered by strong homonuclear photoassociative loss of Li to states in the excited-state $\Sigma$ potentials [1]. We null this background by performing PA on a cycling transition in a mixture of spin-polarized $^{6}$Li and $^{174}$Yb. The Pauli blocking of Li s-wave PA enables the observation of interspecies PA as well as yet unreported Li$_{2}$ photoassociation resonances to excited $\Pi$ states. We intend to utilize knowledge of the interspecies spectrum to perform Raman spectroscopy on the electronic ground state of LiYb, moving towards the coherent production of polar ultracold molecules with a paramagnetic degree of freedom. [1] R. Roy, et al. Phys. Rev. A. 94, 033413 (2016). [Preview Abstract] |
Thursday, June 8, 2017 12:18PM - 12:30PM |
N6.00010: A new apparatus for enhanced optical and electric control of ultracold KRb molecules Giacomo Valtolina, Jacob Covey, Luigi De Marco, Kyle Matsuda, William Tobias, Jun Ye Ultracold molecules represent an ideal platform for studying many-body physics with long-range dipolar interactions. The field of ultracold polar molecules has recently made enormous progress and many different bi-alkali molecules have been produced in their ground state. Recently, dipolar spin-exchange interactions and many-body dynamics have been observed with Fermionic KRb molecules in an optical lattice, and low-entropy samples in a lattice have been realized. However, the ability to apply large electric fields to polarize the molecules has been limited to several kV/cm. Additionally, high resolution in situ has been lacking for polar molecules despite the enormous progress in the quantum gas field. We present a new apparatus for producing Fermionic KRb molecules where stable, homogeneous electric fields in the range of 30 kV/cm are expected, while also accomodating arbitrary gradients in two dimensions. This apparatus is designed for high resolution addressing and detection, and imaging resolutions well below 1 micron are expected. We present details on this apparatus and its construction, and describe the procedure used to produce ultracold gases of atoms and molecules. Further work will lead to high resolution detection of strongly dipolar quantum systems. [Preview Abstract] |
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