Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session T2: Invited Session: Nonequilibrium Dynamics in Strongly Interacting Systems |
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Chair: Bryce Gadway, University of Illinois Room: Union ABC |
Friday, June 12, 2015 8:00AM - 8:30AM |
T2.00001: Demagnetization Dynamics of a Unitary Fermi Gas Invited Speaker: J.H. Thywissen We observe the spin dynamics of a quantum degenerate Fermi gas of $^{40}$K near an s-wave interaction resonance. The starting point of our measurements is a transversely spin-polarized gas, where each atom is in a superposition of the lowest two Zeeman eigenstates. In the presence of an external gradient, a spin texture develops across the cloud, which drives diffusive spin currents. Spin transport is described with two coefficients: $D_0^\perp$, the transverse spin diffusivity, and $\gamma$, the Leggett-Rice parameter. Diffusion is a dissipative effect that increases the entropy of the gas, eventually creating a mixture of spin states. $\gamma$ parameterizes the rate at which spin current precesses around the local magnetization. Using a spin-echo sequence, we measure the transport parameters for a range of interaction strengths and temperatures. At unitarity, we find $D_0^\perp = 2.3(4)\,\hbar/m$ and $\gamma = 1.08(9)$, where $m$ is the atomic mass. In the limit of zero temperature, $\gamma$ and $D_0^\perp$ are scale-invariant universal transport parameters of the unitary Fermi gas. The value of $D_0^\perp$ reveals strong scattering in the unitary gas, and is near its proposed quantum limit, such that the inferred value of the transport lifetime $\tau_\perp$ is comparable to $\hbar/\epsilon_F$. This raises the possibility that incoherent transport may play a role. The nonzero value of $\gamma$ tells us that spin waves in unitary Fermi gas are dispersive, or in other words, that the gas has a spin stiffness in the long-wavelength limit. Time permitting, we will also discuss a time-resolved measurement of the contact, through which we observe the microscopic transformation of the gas from ideal to strongly correlated. [Preview Abstract] |
Friday, June 12, 2015 8:30AM - 9:00AM |
T2.00002: Quantum distillation of bosons Invited Speaker: David Weiss The non-equilibrium dynamics of many-body quantum systems present a series of challenges for theory and opportunities for cold atom experiments. I will describe an experiment in which a bundle of initially trapped superfluid 1D Bose lattice gases is quenched to an untrapped, flat lattice potential. This simple experimental situation in the intermediate coupling regime (U/J between 4 and 9.6) leads to interesting dynamics. These include the progressive dissolution of a fraction of the doublons, as well as the quantum distillation and long term confinement of singlons out of and within the central, doublon-dominated region. We measure these processes by combining absorption imaging, photoassociation and 3-body loss to separately reconstruct the spatial distributions of the expectation values of singlons, doublons and triplons. The qualitative dynamics is reproduced by a Gutzwiller mean field model and the essence of the experiment can be understood by considering simple spatial pictures of site occupancies. [Preview Abstract] |
Friday, June 12, 2015 9:00AM - 9:30AM |
T2.00003: Interplay of spin and motional dynamics in ultracold atoms and molecules Invited Speaker: Kaden Hazzard Several recent ultracold experiments have realized many-body ``spin models'' -- systems where interacting spins are frozen in space. One example I will discuss is polar molecules in an optical lattice. By comparing the JILA group's measurements of far-from-equilibrium molecule dynamics with theoretical predictions, we were able to characterize the spin Hamiltonian and benchmark a new numerical algorithm. Even richer possibilities exist \textit{beyond} spin models, where both spin and motional degrees of freedom evolve dynamically. Such interplay of spin and motion underlies exotic phenomena such as high-temperature superconductivity. I will describe how the unique properties of emerging ultracold systems -- \textit{nonreactive} ultracold molecules, Rydberg atoms, and alkaline earth atoms -- make possible the independent control of the spins, their motion, and the spin-motion coupling. [Preview Abstract] |
Friday, June 12, 2015 9:30AM - 10:00AM |
T2.00004: Experimental investigations of the resonant dipole-dipole interaction between cold Rydberg atoms Invited Speaker: Antoine Browaeys This talk will present our on-going effort to control the dipole-dipole interaction between cold Rydberg atoms. In our experiment, we trap individual atoms in two-dimensional arrays of optical tweezers separated by few micrometers and excite them to Rydberg states using lasers. The arrays are produced by a spatial light modulator, which shapes the dipole trap beam. We can create almost arbitrary geometries of the arrays [1]. We have measured the van der Waals interaction between two individual atoms [2], and show efficient Rydberg blockade in arrays of three atoms [3]. We have also demonstrated the control of the interaction between atoms with microwave and DC electric fields [4]. We observe in particular the coherent energy exchange between two atoms resulting from their dipole-dipole interaction [5]. This control of the interaction will find applications in quantum state engineering, quantum information and quantum simulation. \\[4pt] [1] F. Nogrette, H. Labuhn, S. Ravets, D. Barredo, L. B\'{e}guin, A. Vernier, T. Lahaye, A. Browaeys, ``Single- atom trapping in holographic 2D arrays of microtraps with arbitrary geometries,'' Phys. Rev. X \textbf{4}, 021034 (2014).\\[0pt] [2] L. Beguin, A. Vernier, R. Chicireanu, T. Lahaye, and A. Browaeys, ``Direct measurement of the van der Waals interaction between two single atoms,'' Phys. Rev. Lett. \textbf{110}, 263201 (2013). \\[0pt] [3] D. Barredo, S. Ravets, H. Labuhn, L. B\'{e}guin, A. Vernier, F. Nogrette, T. Lahaye, A. Browaeys, ``Demonstration of strong Rydberg blockade in three-atom systems with anisotropic interactions,'' Phys. Rev. Lett. \textbf{112}, 183002 (2014).\\[0pt] [4] S. Ravets, H. Labuhn, D. Barredo, L. B\'{e}guin, T. Lahaye, A. Browaeys, ``Coherent dipole-dipole coupling between two single atoms at a F\"{o}rster resonance'', Nature Physics \textbf{10}, 914 (2014).\\[0pt] [5] D. Barredo, H. Labuhn, S. Ravets, T. Lahaye, A. Browaeys, C. S. Adams, ``Coherent Excitation Transfer in a `Spin Chain' of Three Rydberg Atoms,'' arXiv:1408.1055 [Preview Abstract] |
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