Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session P1: Ferromagnetism and Upper Branch Physics |
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Chair: Edward Taylor, Ohio State University Room: 200A |
Thursday, June 6, 2013 2:00PM - 2:30PM |
P1.00001: Quench dynamics in strongly correlated Bose-Hubbard chains Invited Speaker: Hanns-Christoph Naegerl We present a series of experiments in the context of 1D physics with ultracold atoms, combining optical lattice potentials with the capability to tune the strength of the onsite particle interaction U. For an array of tilted 1D chains with site-to-site tilt E and initial unity occupation we record the dynamics after a quench to the phase transition point U$\approx $E by monitoring the number of doublons created as a function of time after the quench. We observe characteristic oscillations from which we deduce a shift of the resonance condition as time progresses. For U/2$\approx $E and U/3$\approx $E we observe coupling to next-nearest neighbors and beyond. [Preview Abstract] |
Thursday, June 6, 2013 2:30PM - 3:00PM |
P1.00002: Ferromagnetism of strongly interacting Fermi gases in the upper branch of Feshbach resonances Invited Speaker: Shizhong Zhang In this talk, I discuss the question of ferromagnetism in strongly interacting two-component Fermi gases in the upper branch of Feshbach resonances. I first examine theoretically the necessary conditions for the system to be in the upper branch and formulate a theoretically tractable approach based on variational wave functions. Relevant experiments will be reviewed in light of the above theoretical understanding and their implication for the occurrence of ferromagnetism will be discussed critically. In particular, I discuss in some detail the recent MIT colliding cloud experiment and argue that at short times, the bouncing of the clouds indicates upper branch physics with effective repulsive interaction favoring phase separated configuration of two spin components [1]. \\[4pt] [1] E. Taylor, S. Zhang, W. Schneider and M. Randeria, Phys.Rev.A 84 063622 (2011) [Preview Abstract] |
Thursday, June 6, 2013 3:00PM - 3:12PM |
P1.00003: Correlations of the metastable branch of harmonically-trapped one-dimensional two-component Fermi gases Seyed Ebrahim Gharashi, D. Blume We present highly-accurate energy spectra and eigen functions of small harmonically-trapped one-dimensional two-component Fermi gases with interspecies $\delta$-function interactions, and analyze the correlations of the metastable crossover branch with effectively repulsive and attractive interactions. Structural expectation values are presented as a function of the interspecies coupling strength and related to cold atom tunneling experiments. Moreover, we show that the eigenstate $\psi_{adia}$ of the infinitely strongly-interacting system with $n_1+n_2>2$ and $|n_1-n_2| < n$ ($n_1$ and $n_2$ denote the number of fermions of components 1 and 2, respectively, and $n_1+n_2 = n$), which is reached experimentally by adiabatically changing the system parameters, does not, as previously proposed, coincide with the wave function $\psi_{G}$ obtained by applying a generalized Fermi-Fermi mapping function to the eigen function of the non-interacting single-component Fermi gas. [Preview Abstract] |
Thursday, June 6, 2013 3:12PM - 3:24PM |
P1.00004: Investigation of the Fermi-Hubbard model with $^{6}$Li in an optical lattice R.A. Hart, P.M. Duarte, T.-L. Yang, R.G. Hulet We present our results on investigation of the physics of the Fermi-Hubbard model using an ultracold gas of $^{6}$Li loaded into an optical lattice. We use all-optical methods to efficiently cool and load the lattice beginning with laser cooling on the $2S_{1/2}\rightarrow 2P_{3/2}$ transition and then further cooling using the narrow $2S_{1/2}\rightarrow 3P_{3/2}$ transition to T $\sim$ 59 $\mu$K\footnote{P. M. Duarte et al., Phys. Rev. A \textbf{84}, 061406 (2011).}. The second stage of laser cooling greatly enhances loading to an optical dipole trap where a two spin state mixture of atoms is evaporatively cooled to degeneracy. We then adiabatically load $\sim$$10^{6}$ degenerate fermions into a 3D optical lattice formed by three orthogonal standing waves of 1064 nm light. Overlapped with each of the three lattice beams is a non-retroreflected beam at 532 nm. This light cancels the harmonic trapping caused by the lattice beams, which extends the number of lattice sites over which a N\'eel phase can exist and may allow evaporative cooling in the lattice. By using Bragg scattering of light\footnote{T. A. Corcovilos et al., Phys. Rev. A \textbf{81}, 013415 (2010).}, we investigate the possibility of observing long-range antiferromagnetic ordering of spins in the lattice. [Preview Abstract] |
Thursday, June 6, 2013 3:24PM - 3:36PM |
P1.00005: Quantum magnetism of ultracold fermions in an optical lattice Daniel Greif, Thomas Uehlinger, Gregor Jotzu, Leticia Tarruell, Tilman Esslinger Quantum magnetism describes quantum many-body states with spins coupled by exchange interactions. At low temperatures this leads to short- and long-range magnetic ordering, which is for example the case in spin-liquids, valence-bond solids and antiferromagnets. We report on the observation of magnetic spin correlations on neighboring sites of a Fermi gas in an optical lattice. The key to obtaining and detecting the short-range magnetic order is an entropy redistribution technique in a tunable-geometry optical lattice. We load a low-temperature two-component gas with repulsive interactions into either a dimerized or anisotropic simple cubic lattice. The correlations manifest as an excess number of singlets as compared to triplets consisting of two atoms with opposite spins. For the anisotropic lattice, we determine the transverse spin correlator from the singlet-triplet imbalance and observe antiferromagnetic correlations along one spatial axis. [Preview Abstract] |
Thursday, June 6, 2013 3:36PM - 3:48PM |
P1.00006: Second sound and the superfluid fraction in a resonantly interacting Fermi gas Leonid Sidorenkov, Meng Khoon Tey, Rudolf Grimm, Yan-Hua Hou, Lev Pitaevskii, Sandro Stringari Key signatures of superfluidity, like the absence of viscosity and the formation of quantized vortices, have already been observed in ultracold gases. Surprisingly, a direct observation of second sound has so far remained elusive. Second sound is an entropy wave, characterized by local out-of-phase oscillation of the normal and the superfluid component. Here we report on the first observation of second sound propagating in a superfluid Fermi gas. The ability to measure the speed of second sound allows us to extract the temperature dependence of the superfluid density. So far this quantity has been inaccessible in strongly interacting Fermi gas. Our results complement recent measurements of the equation of state for resonantly interacting Fermi gas and provide valuable information for understanding the elementary excitation spectrum of this system. [Preview Abstract] |
Thursday, June 6, 2013 3:48PM - 4:00PM |
P1.00007: Pauli paramagnetism of an ideal Fermi gas Timur M. Rvachov, Yeryoung Lee, Tout T. Wang, Jae-Hoon Choi, Wolfgang Ketterle, Myoung-Sun Heo We show how to use trapped ultracold atoms to measure the magnetic susceptibility of a two-component Fermi gas. The method is illustrated for a non-interacting gas of $^6$Li, using the tunability of interactions around a wide Feshbach resonances. The susceptibility versus effective magnetic field is directly obtained from the inhomogeneous density profile of the trapped atomic cloud. The wings of the cloud realize the high field limit where the polarization approaches 100\%, which is not accessible for an electron gas. This work is mainly pedagogical in nature. [Preview Abstract] |
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