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 G6: One-Dimensional Gases and Nanofibers |
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Chair: Vladan Vuletic, Massachusetts Institute of Techology Room: 552AB |
Wednesday, May 25, 2016 8:00AM - 8:12AM |
G6.00001: Finite-temperature hydrodynamics for a 1D Bose gas and its application to breathing-mode oscillations in position and momentum spaces. Karen Kheruntsyan, Isabelle Bouchoule We develop a finite-temperature hydrodynamic approach for harmonically trapped 1D Bose gases and use it to describe the phenomenon of frequency quasi-doubling in the breathing-mode oscillation of the momentum distribution of the gas. The quasi-doubling here refers to the frequency of oscillation relative to the oscillations of the real-space density distribution, invoked by a sudden confinement quench. For problems with known initial (equilibrium) momentum distributions, our approach extends the utility of the hydrodynamic theory to describe the finite-temperature non-equilibrium dynamics not only in position space, but also in momentum space. The approach leads to insightful analytic results in both the weakly-interacting quasi-condensate and strongly-interacting Tonks-Girardeau (TG) regimes. It allows us to discern the contribution of the hydrodynamic velocity field and that of thermal excitations, hence explaining the mechanism behind the phenomenon of frequency quasi-doubling and its disappearance: We find that, at any finite temperature, this is governed by the quench strength, rather than by, e.g., a naively conjectured regime-crossover from the ideal Bose gas to the quasi-condensate (or TG) regime. [Preview Abstract] |
Wednesday, May 25, 2016 8:12AM - 8:24AM |
G6.00002: Observing the 1D-3D Crossover in a Spin-Imbalanced Fermi Gas Melissa C. Revelle, Jacob A. Fry, Ben A. Olsen, Randall G. Hulet Trapped two-component Fermi gases phase separate into superfluid and normal phases when their spin populations are imbalanced. In 3D, a balanced superfluid core is surrounded by shells of partially polarized and normal phases\footnote{B. A. Olsen et al., Phys. Rev. A. 92, 063616 (2015).}, while in 1D, the balanced superfluid occupies the low density wings\footnote{Y.A. Liao et al., Nature 467, 567 (2010).}. We explored the crossover from 3D to 1D using a two-spin component ultracold atomic gas of $^{6}$Li prepared in the lowest two hyperfine sublevels, where the interactions are tuned by a Feshbach resonance. The atoms are confined to 1D tubes where the tunneling rate $t$ between tubes is varied by changing the depth of a 2D optical lattice. We observe the transition from 1D to 3D-like phase separation by varying $t$ and interaction strength which changes the pair binding energy $\epsilon_{B}$. We find a universal scaling of the dimensional crossover with $t/\epsilon_{B}$, in agreement with previous theory\footnote{M. Parish et al., PRL 99, 250403 (2007).}. The crossover region is believed to be the most promising to find the exotic FFLO superfluid phase. [Preview Abstract] |
Wednesday, May 25, 2016 8:24AM - 8:36AM |
G6.00003: Measuring the Speed of Sound in a 1D Fermi Gas Jacob Fry, Melissa Revelle, Randall Hulet We report measurements of the speed of sound in a two-spin component, 1D gas of fermionic lithium. The 1D system is an array of one-dimensional tubes created by a 2D optical lattice. By increasing the lattice depth, the tunneling between tubes is sufficiently small to make each an independent 1D system. To measure the speed of sound, we create a density notch at the center of the atom cloud using a sheet of light tuned far from resonance. The dipole force felt by both spin states will be equivalent, so this notch can be thought of as a charge excitation \footnote{A. Recati, P. O. Fedichev, W. Zwerger, and P. Zoller, \textbf{Phys. Rev. Lett} 90, 020401 (2003).}. Once this beam is turned off, the notch propagates to the edge of the atomic cloud with a velocity that depends on the strength of interatomic interactions. We control interactions using a magnetically tuned Feshbach resonance, allowing us to measure the speed of sound over a wide range of interaction. This method may be used to extract the Luttinger parameter vs. interaction strength. [Preview Abstract] |
Wednesday, May 25, 2016 8:36AM - 8:48AM |
G6.00004: Direct Observation of Spin- and Charge-Density Waves in a Luttinger Liquid Chenglin Cao, Andrew Marcum, Arif Mawardi Ismail, Francisco Fonta, Kenneth O'Hara At low energy, interacting fermions in one dimension (e.g. electrons in quantum wires or fermionic atoms in 1D waveguides) should behave as Luttinger liquids.~ In stark contrast to Fermi liquids, the low-energy elementary excitations in Luttinger liquids are collective sound-like modes that propagate independently as spin-density and/or charge-density (i.e. particle-density) waves with generally unequal, and interaction-dependent, velocities.~ Here we aim to unambiguously confirm this hallmark feature of the Luttinger liquid -- the phenomenon of spin-charge separation -- by directly observing in real space the dynamics of spin-density and "charge"-density waves excited in an ultracold gas of spin-1/2 fermions confined in an array of 1D optical waveguides.~ Starting from a two-component mixture of $^{6}$Li atoms harmonically confined along each of the 1D waveguides, we excite low lying normal modes of the trapped system -- namely the spin dipole and density dipole and quadrupole modes -- and measure their frequency as a function of interaction strength.~ Luttinger liquid theory predicts that the spin dipole frequency is strongly dependent on interaction strength whereas the density dipole and quadrupole mode frequencies are relatively insensitive.~~ We will also discuss extending our approach to exciting localized spin density and particle density wavepackets which should propagate at different velocities. [Preview Abstract] |
Wednesday, May 25, 2016 8:48AM - 9:00AM |
G6.00005: Observation of Dynamical Fermionization in 1D Bose Gases Neel Malvania, Lin Xia, Wei Xu, Joshua M. Wilson, Laura A. Zundel, Marcos Rigol, David S. Weiss The momentum distribution of a harmonically trapped 1D Bose gases in the Tonks-Girardeau limit is expected to undergo dynamical fermionization [1]. That is, after the harmonic trap is suddenly turned off, the momentum distribution steadily transforms into that of an ideal Fermi gas in the same initial trap. We measure 1D momentum distributions at variable times after such a quench, and observe the predicted dynamical fermionization. In addition to working in the strong coupling limit, we also perform the experiment with intermediate coupling, where theoretical calculations are more challenging. [1] M. Rigol, A. Muramatsu, PRL 94, 240403 (2005); A. Minguzzi, D. M. Gangardt, PRL 94, 240404 (2005). [Preview Abstract] |
Wednesday, May 25, 2016 9:00AM - 9:12AM |
G6.00006: Precision measurements of momentum distribution of Tonks-Girardeau gas. Joshua M. Wilson, Lin Xia, Wei Xu, Neel Malvania, Laura A. Zundel, Marcos Rigol, David S. Weiss We report on precision measurements of the momentum distributions of 1D Bose gases over a range of initial temperatures and coupling strengths. We compare our results with unbiased quantum Monte Carlo simulations. We use the comparison with theory to understand the nature of the adiabatic loading from a Bose-Einstein Condensate in 3D to an array of 1D tubes. [Preview Abstract] |
Wednesday, May 25, 2016 9:12AM - 9:24AM |
G6.00007: Correlations in light propagation in one-dimensional waveguides Juha Javanainen, Janne Ruostekoski We study light propagation between atoms in a one-dimensional waveguide both analytically and using numerical simulations. We employ classical electrodynamics, but in the limit of low light intensity the results are essentially exact also for quantum mechanics. We characterize the cooperative interactions between the atoms mediated by the electromagnetic field. The focus is on resonance shifts for various statistics of the positions of the atoms, such as statistically independent positions or atoms in a regular lattice. These shifts, potentially important if 1D waveguides are to be used in metrology, are different from the usual resonance shifts found in three spatial dimensions. [Preview Abstract] |
Wednesday, May 25, 2016 9:24AM - 9:36AM |
G6.00008: Light imprisonment in a nanofiber mode by an ensemble of few cold atoms P. Solano, S. L. Rolston, L. A. Orozco, J. P. Clemens, P. R. Rice We study the escape of light emitted by cold Rb atoms in the vicinity of an optical nanofiber. We excite the atoms with a pulse propagating perpendicular to the nanofiber, which turns off faster than the atom natural lifetime. We use time correlated single photon counting techniques to measure the decay of the emitted light. For very low optical density we see the natural lifetime reduced by the presence of the nanofiber and its only available mode, while for higher optical densities the decay time can be many times longer. Provided that an average atom can absorb as much as 30\% of the light in the mode, we only need few atoms to observe light imprisonment. We explore radiation trapping and the presence of other collective phenomena to explain this effect. [Preview Abstract] |
Wednesday, May 25, 2016 9:36AM - 9:48AM |
G6.00009: Polarimetric measurement of the motion of trapped atoms around a nanofiber F. K. Fatemi, P. Solano, L. A. Orozco, S. L. Rolston Polarimetry is an important tool for probing the classical and quantum dynamics of a collection of trapped atoms. We observe the birefringence induced by trapped Rb atoms around an optical nanofiber by measuring the polarization change of an off-resonant probe. The signal from the weak, non-destructive probe is amplified using heterodyne detection. We observe the dynamical response of the trapped atoms to a transient modification of the trapping potential. This provides a direct measurement of the trapping frequencies associated with the axial and transverse potentials. The presence of large longitudinal fields in the evanescent field of the fiber complicates polarimetry, presenting significant challenges for the observation of atomic spin dynamics through Faraday rotation measurements. [Preview Abstract] |
Wednesday, May 25, 2016 9:48AM - 10:00AM |
G6.00010: Dimension control of Superradiance Tyler Hill We develop a theory for quantum dipole-dipole coupling when the electromagnetic fields are confined to an open line, open plane, or open space, commensurate with experimental capability for collective atomic effects subject to dimensional confinement. Our mathematical model naturally interpolates for all real dimension between one dimension for the line to three dimensions for open space. We show how superradiant emission can be controlled by dimensional confinement, including near-field and dipole-orientation effects, and we propose a two-dimensional confinement experiment to test our theory's efficacy. [Preview Abstract] |
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