Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session C5: BEC with Strong Interactions |
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Chair: Philip Russ, University of Illinois, Urbana Room: 551AB |
Tuesday, May 24, 2016 2:00PM - 2:12PM |
C5.00001: Bragg Spectroscopy of a Strongly-Interacting Homogeneous BEC: probing quantum depletion Raphael Lopes, Christoph Eigen, Adam Baker, Nir Navon, Zoran Hadzibabic, Robert Smith We will present Bragg spectroscopy measurements performed on a homogeneous Bose-Einstein condensate (BEC) as a function of interaction strength. The width and position of the Bragg resonance reveal the momentum distribution and energy shift of the ground state, respectively. We observe that the width increases as a function of interaction strength and interpret this behavior as a result of quantum depletion of the condensate, induced by interactions. The central frequency of the resonance grows linearly with the interaction strength (mean-field behavior) but is reduced as the interaction strength further increases; being completely suppressed at high values. [Preview Abstract] |
Tuesday, May 24, 2016 2:12PM - 2:24PM |
C5.00002: Clock shifts in the Unitary Bose Gas Richard Fletcher, Jay Man, Raphael Lopes, Nir Navon, Robert Smith, Zoran Hadzibabic Clock shifts are interaction-induced changes in the transition frequency between atomic spin states. So-called because of their importance as systematic errors in atomic clocks, they reveal details of both the interaction energy within a gas and the particle correlations. In this work, we employ a RF-injection technique to rapidly project a thermal Bose gas into the unitary regime on a timescale much shorter than three-body losses. Working with a two-state system, one of which exhibits strong intrastate interactions, we carry out Ramsey spectroscopy to extract the variation in the clock shift across a Feshbach resonance. Thanks to the relationship between these shifts and particle correlations, we use our measurements to infer the contact as a function of both interaction strength and degeneracy. This quantity plays a central role in the many-body physics of strongly correlated systems, offering a link between few-body and thermodynamic behaviour. [Preview Abstract] |
Tuesday, May 24, 2016 2:24PM - 2:36PM |
C5.00003: Stability of a Unitary Homogeneous Bose-Einstein Condensate Robert Smith, Christoph Eigen, Adam Barker, Raphael Lopes, Nir Navon, Zoran Hadzibabic We will present the first measurements exploring the behavior of a unitary homogeneous Bose-Einstein Condensate (BEC). Starting with BEC of $^{39}$K in an optical box potential we utilize an RF injection procedure to rapidly transfer the atoms into a strongly interacting state and measure the resultant atom loss. We then explore how the dependence of loss rate on density varies as we tune the interaction strength up to and into the unitary regime. [Preview Abstract] |
Tuesday, May 24, 2016 2:36PM - 2:48PM |
C5.00004: Universal dynamics in a Unitary Bose Gas Catherine Klauss, Xin Xie, Jose D'Incao, Deborah Jin, Eric Cornell We investigate the dynamics of a unitary Bose gas with an $^{85}$Rb BEC, specifically to determine whether the dynamics scale universally with density. We find that the initial density affects both the (i) projection of the strongly interacting many-body wave-function onto the Feshbach dimer state when the system is rapidly ramped to a weakly interacting value of the scattering length $a$ and (ii) the overall decay rate to deeper bound states. We will present data on both measurements across two orders of magnitude in density, and will discuss how the data illustrate the competing roles of universality and Efimov physics. [Preview Abstract] |
Tuesday, May 24, 2016 2:48PM - 3:00PM |
C5.00005: Initial Atom Loss Rate after the Sudden Ramp of a BEC to Unitarity Eric Braaten, Abhishek Mohaptra, D. Hudson Smith The quantum-degenerate unitary Bose gas has been studied in an experiment at JILA in which a Bose-Einstein condensate was quickly ramped to infinite scattering length. The sudden approximation can be used to calculate the probability for creating Efimov trimers. A trimer that is created in a region of the BEC where its decay rate is faster than its reaction rate from atom-trimer scattering can contribute to the initial atom loss rate. We use universal 3-body and 4-body results to estimate the initial atom loss rate. [Preview Abstract] |
Tuesday, May 24, 2016 3:00PM - 3:12PM |
C5.00006: Hydrodynamics of a unitary Bose gas Jay Man, Richard Fletcher, Raphael Lopes, Nir Navon, Rob Smith, Zoran Hadzibabic In general, normal-phase Bose gases are well described by modelling them as ideal gases. In particular, hydrodynamic flow is usually not observed in the expansion dynamics of normal gases, and is more readily observable in Bose-condensed gases. However, by preparing strongly-interacting clouds, we observe hydrodynamic behaviour in normal-phase Bose gases, including the ‘maximally’ hydrodynamic unitary regime. We avoid the atom losses that often hamper experimental access of this regime by using radio-frequency injection, which switches on interactions much faster than trap or loss timescales. At low phase-space densities, we find excellent agreement with a collisional model based on the Boltzmann equation. At higher phase-space densities our results show a deviation from this model in the vicinity of an Efimov resonance, which cannot be accounted for by measured losses. [Preview Abstract] |
Tuesday, May 24, 2016 3:12PM - 3:24PM |
C5.00007: Bose polarons in the strongly interacting regime Dhruv Kedar, Ming-Guang Hu, Michael Van de Graaff, John Corson, Eric Cornell, Deborah Jin Impurities immersed in and interacting with a Bose-Einstein condensate (BEC) are predicted to form quasiparticle excitations called Bose polarons. I will present experimental evidence of Bose polarons in cold atoms obtained using radio-frequency spectroscopy to measure the excitation spectrum of fermionic K-40 impurities interacting with a BEC of Rb-87 atoms. We use an interspecies Feshbach resonance to tune the interactions between the impurities and the bosons, and we take data in the strongly interacting regime. [Preview Abstract] |
Tuesday, May 24, 2016 3:24PM - 3:36PM |
C5.00008: The Role of Temperature in the Efimov Effect D. Luo, J. H. V. Nguyen, R. G. Hulet The formation of Efimov trimer states requires the system to be in the universal regime, where the temperature is low enough that the thermal de Broglie wavelength is large compared to the range of the interaction between the particles. While the zero-temperature limit of the Efimov effect has been carefully studied by mapping the three-body recombination rate as a function of the scattering length, how these states are affected by non-zero temperature is less well-understood. We explore the role of temperature in the Efimov effect by measuring the location of the recombination minimum $a_{2}^{+}$ and width $\eta_{*}$ for a gas of $^7$Li atoms in a temperature range of 0.1 to 7 $\mu K$. Our results are compared with a similar study with Cs atoms\footnote{B. Huang, L. A. Sidorenkov, \& R. Grimm, Phys. Rev. A 91, 063622 (2015).}. Contrary to that work we find that $a_{2}^{+}$ depends linearly on $T$ at low temperature. We speculate that the difference is explained by the fact that $k_{th} r_{vdW} \ll 1$ for $^7$Li in our temperature range, and thus, unlike Cs, is deeply in the universal regime. [Preview Abstract] |
Tuesday, May 24, 2016 3:36PM - 3:48PM |
C5.00009: BEC of $^{41}$K in a Fermi sea of $^6$Li Rianne S. Lous, Isabella Fritsche, Bo Huang, Michael Jag, Marko Cetina, Jook T.M. Walraven, Rudolf Grimm We report on the production of a $^{41}$K Bose-Einstein condensate (BEC) immersed in a degenerate two-component $^6$Li Fermi sea. After evaporation in an optical dipole trap, we obtain $1.2\times10^4$ $^{41}$K atoms with a 55\% BEC fraction and a Fermi sea with $T/T_F< 0.1$, consisting of $1.8\times 10^5$ $^6$Li atoms in each of the lowest two spin states. This opens the way to study the collective behavior of a mass-imbalanced mixture of two coupled superfluids. The double-degenerate Fermi-Bose mixture also enables the study of interacting bosonic impurities in a Fermi sea. Using loss spectroscopy, we observe the $335.8\,\text{G}$ Feshbach resonance, which is comparable to the one between $^{6}$Li and the fermionic $^{40}$K isotope exploited in our previous studies on the quantum many-body dynamics of fermionic impurities in a Fermi sea \footnote{Cetina et al., Phys. Rev. Lett. \textbf{115}, 13502 (2015)}. Investigating the interacting bosonic impurities enables the direct comparison of the role of quantum statistics for fermionic and bosonic impurities. [Preview Abstract] |
Tuesday, May 24, 2016 3:48PM - 4:00PM |
C5.00010: s-wave resonant short-range interactions in a $d$-dimensional finite volume Shangguo Zhu, Shina Tan It has been known that the energy spectra of few or many particles with short-range interactions in a finite periodic box are shifted according to the size of the box. In particular, the two-body energy levels in a large box are approximately described by the L\"{u}scher's formula. Here we study the energy of one particle scattered by a resonant s-wave short-range center in a $d$-dimensional finite volume. When $d=6$, this one-body problem is closely related to the scattering of three particles in a three-dimensional box with a resonant three-body interaction. For $d\ge4$, we derive systematic expansions of the low-lying energy eigenvalues at large box sizes. [Preview Abstract] |
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