Bulletin of the American Physical Society
45th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 59, Number 8
Monday–Friday, June 2–6, 2014; Madison, Wisconsin
Session C4: Ultracold Fermi Gases 
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Chair: John Thomas, North Carolina State University Room: Ballroom B 
Tuesday, June 3, 2014 2:00PM  2:12PM 
C4.00001: Engineered pwave collisions in ultracold Fermionic systems Lauren Aycock, Dina Genkina, Benjamin Stuhl, Ian Spielman This experiment demonstrates the pwave and higher odd partial waves describing interactions in a spin polarized Fermi gas: critical for engineering utlracold Fermi gases to support Majorana fermions [1]. Here, we describe an experiment which combines known experimental techniques for modifying interactions between atoms in a unique way to artificially engineer pwave collisions in ultracold Fermionic systems. Using swave Feshbach resonances to tune interactions in degenerate Fermi gases have been very fruitful in studying manybody quantum physics; however, pWave Feshbach resonances are limited in their usefulness by large inelastic loss rates [2,3]. In combination with an sWave Feshbach resonance, we modify the fermionic interaction by laserdressing. We already demonstrated that this technique introduces d and gwave contributions to the swave scattering in degenerate Bose gases [4].\\[4pt] [1] C. Zhang, S. Tewari, R. M. Lutchyn, S. Das Sarma, \textit{Phys. Rev. Lett.} \textbf{101}, 160401 (2008). \newline [2] C. Chin, R. Grimm, P. Julienne, E. Tiesinga, \textit{Rev. Mod. Phys.} \textbf{82}, 1225 (2010). \newline [3] C. A. Regal, C. Ticknor, J. L. Bohn, D. S. Jin, \textit{Phys. Rev. Lett.} \textbf{90}, 053201 (2003). \newline [4] R. A. Williams, et al. \textit{Science} \textbf{335}, 314 (2012). [Preview Abstract] 
Tuesday, June 3, 2014 2:12PM  2:24PM 
C4.00002: Optical Control of Collisional Interactions in $^{6}$Li using Dark Molecular States Arunkumar Jagannathan, Nithya Arunkumar, Ethan Elliot, James Joseph, John Thomas We are developing ``darkstate'' twooptical field methods to control interactions in $^{6}$Li. Although external magnetic fields are typically used to tune the interaction strength in fermionic atoms near a Feshbach resonance, optical tuning methods can provide rapid temporal control and highresolution spatial control thus enabling the study of nonequilibrium strongly interacting Fermi gases. However, optical tuning suffers from heating due to spontaneous scattering, which can be suppressed by a second optical field. We will report on the measurement of loss spectrum as a function of magnetic field and laser detuning near Feshbach resonances in $^{6}$Li and our progress on twooptical field loss suppression. [Preview Abstract] 
Tuesday, June 3, 2014 2:24PM  2:36PM 
C4.00003: Noninteracting Fermi gas in a magnetic quadrupole trap To Chun Johnathan Lau, Olga Goulko, Fr\'ed\'eric Chevy, Carlos Lobo A noninteracting gas of spin polarised 6Li Fermi gas in a magnetic quadrupole trap which is not in thermal equilibrium can nevertheless show thermal signatures in some cases. This puzzling behaviour can be seen by measuring the doubly integrated momentum distribution along a particular axis. This distribution can be extremely close to a Gaussian from which we can extract a temperature. However, we show, using molecular dynamics simulations that the temperature thus measured is generally different along different axes. We provide a general explanation of this phenomenon based on ergodicity and check it with further simulations. [Preview Abstract] 
Tuesday, June 3, 2014 2:36PM  2:48PM 
C4.00004: Anomalous minimum in the shear viscosity of a Fermi gas James Joseph, Ethan Elliott, John Thomas We measure the static shear viscosity in a twocomponent Fermi gas near a broad collisional (Feshbach) resonance as a function of the interaction strength and energy. We implement new and more precise methods in comparison to our previous measurement of shear viscosity by utilizing an elliptical trap with a 1:2.7:33 aspect ratio and imaging the expanding atom cloud from two orthogonal directions. We investigate the dependence of the shear viscosity $\eta $ as a function of the interaction strength 1/(k$_{\mathrm{F}}$ a), where a is the swave scattering length and k$_{\mathrm{F}}$ is the Fermi wave vector for an ideal gas at the trap center. We find that near resonance at constant energy, $\eta $ has both a quadratic and linear dependence on 1/(k$_{\mathrm{F}}$ a). Further, we find the linear contribution diminishes as a function of energy while the quadratic dependence remains constant. At low energy just above the critical temperature we find the minimum in shear viscosity is less than the resonant value and is significantly shifted toward the BEC side of resonance to 1/(k$_{\mathrm{F}}$ a) $\approx $ 0.2. http://arxiv.org/abs/1311.2049 [Preview Abstract] 

C4.00005: ABSTRACT WITHDRAWN 
Tuesday, June 3, 2014 3:00PM  3:12PM 
C4.00006: The Scattering and Coherence of a Fermi Polaron Marko Cetina, Michael Jag, Rianne Lous, Florian Schreck, Rudolf Grimm, Rasmus S{\O}rensen, Georg Bruun We probe the coherence of a strongly interacting $^{40}$K impurity in a Fermi sea of ${^6}$Li atoms using timeresolved Ramsey spectroscopy. The measured variation of the coherence with the interaction strength and temperature is wellexplained by the lowenergy scattering of the impurity in the Fermi liquid picture. For very strong interactions, we observe additional dynamics arising from the dressing of the impurity by its environment. [Preview Abstract] 
Tuesday, June 3, 2014 3:12PM  3:24PM 
C4.00007: Observation of scale invariance and conformal symmetry breaking in expanding Fermi gases Ethan Elliott, James Joseph, John Thomas We precisely test scale invariance and examine local thermal equilibrium in the hydrodynamic expansion of a Fermi gas of atoms as a function of interaction strength. After release from an anisotropic optical trap, we observe that a resonantly interacting gas obeys scaleinvariant hydrodynamics, where the mean square cloud size $\langle{\mathbf{r}}^2\rangle=\langle x^2+y^2+z^2\rangle$ expands ballistically (like a noninteracting gas) and the energyaveraged bulk viscosity is consistent with zero, $0.00(0.04)\,\hbar\,n$, with $n$ the density. In contrast, the aspect ratios of the cloud exhibit anisotropic ``elliptic" flow with an energydependent shear viscosity. Tuning away from resonance, we observe conformal symmetry breaking, where $\langle{\mathbf{r}}^2\rangle$ deviates from ballistic flow. [Preview Abstract] 
Tuesday, June 3, 2014 3:24PM  3:36PM 
C4.00008: Local observation of paircondensation in a Fermi gas at unitarity Kristian Fenech, Marcus Lingham, Sascha Hoinka, Chris Vale Ultracold Fermi gases near a Feshbach resonance provide a means to investigate the physics of strongly interacting quantum systems. Through the use of spatially resolved Bragg spectroscopy we are able to measure the homogenous densitydensity response function of a Fermi gas at unitarity. The resulting Bragg response provides a clear signature of paircondensation at temperatures below the superfluid transition temperature. The method used to obtain the local measurement is generalizable to any homogenous parameter which satisfies the local density approximation, providing a new tool that can be used where techniques such as the inverseAbel transform are no longer applicable. [Preview Abstract] 
Tuesday, June 3, 2014 3:36PM  3:48PM 
C4.00009: Dynamics of pair correlations in a strongly interacting polarized Fermi gas Chris Luciuk, Stefan Trotzky, Scott Beattie, Alma Bardon, Edward Taylor, Shizhong Zhang, Joseph Thywissen Radiofrequency (rf) spectroscopy has been used to measure the chemical potential, the molecular binding energy, the quasiparticle dispersion relation, and the contact of Fermi gases in equilibrium. Here we present a dynamic study of Fermidegenerate $^{40}$K that is initially fully polarized in a superposition of two hyperfine states. A magnetic field gradient, combined with transverse spin diffusion, causes the gas to demagnetize. We present results of timeresolved rf spectroscopy, used to observe both contact dynamics at unitarity and the formation of molecular dimers below the Feshbach resonance. The time variation of contact shows how an ideal gas dynamically evolves into a strongly correlated mixture. Molecular dynamics allow us to delineate a metastable regime of repulsive atomic interactions. [Preview Abstract] 
Tuesday, June 3, 2014 3:48PM  4:00PM 
C4.00010: Periodically driven cold fermions in integer Quantum Hall regime Erhai Zhao, Mahmoud Lababidi, Indu Satija We present theoretical results for ultracold fermions in the presence of a constant artificial magnetic field but timeperiodically modulated optical lattices. Besides the familiar integer quantum Hall effect in the stroboscopic limit, we show a series of Floquet topological phases that have no static analog and are unique to periodically driven systems. A hallmark of these phases is the appearance of robust, counterpropagating edge modes. We elucidate the nature of these edge states by considering different driving protocols and then discuss their experimental signatures. [Preview Abstract] 
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