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 C1: DAMOP Thesis Prize |
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Chair: John Bollinger, National Institute of Standards and Technology Room: Regency Ballroom |
Tuesday, June 9, 2015 2:00PM - 2:30PM |
C1.00001: Topology and localization in dipolar spin systems Invited Speaker: Norman Yao Statistical mechanics is the framework that connects thermodynamics to the microscopic world. It hinges on the assumption of equilibration; when equilibration fails, so does much of our understanding. In this talk, I will discuss the non-equilibrium dynamics of strongly-entangled systems. Owing to their natural isolation, quantum optical systems of atoms, ions and molecules are attractive building blocks for probing such many-body phenomena. In the first half, I will present an overview, covering many-body localization and topological bandstructures. In the second half, I will focus on describing how the v = 1/2 fractional Chern insulator arises naturally in a two-dimensional array of driven, dipolar-interacting spins. This topological phase constitutes a fundamentally new state of matter, exhibiting fractionalized excitations, robust chiral edge modes, and lattice-symmetry-protected phase transitions. [Preview Abstract] |
Tuesday, June 9, 2015 2:30PM - 3:00PM |
C1.00002: Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers Invited Speaker: Vivek Tiwari Understanding the fundamental physics of light-harvesting in both, natural and artificial systems is key for the development of efficient light-harvesting technologies. My thesis addresses the following topics, i.) the mechanism underlying the remarkably efficient electronic energy transfer in natural light harvesting antennas, ii.) a femtosecond time-resolved photonumeric technique to quantitatively characterize transient chemical species. This talk will concentrate on the first project, while briefly touching the key ideas of the second project. Light harvesting antennas use a set of closely spaced pigment molecules held in a controlled relative geometry by a protein. It is shown that in certain antenna proteins the excited state electronic energy gaps between the pigments are resonant with a quantum of pigment vibrational energy. With such a vibrational-electronic resonance, anti-correlated motions between the pigments lead to a strong coupling between the electronic and nuclear motions, that is, breakdown of the Born-Oppenheimer approximation, over a wide range of pigment vibrational motions. It is shown that the 2D spectroscopic signatures of the resulting unavoidable nested non-adiabatic energy funnel on the excited states of photosynthetic antennas are consistent with all the reported 2D signatures of long-lived coherent oscillations, including the ones that are not explained by prior models of excited state electronic energy transfer. Extensions that account for both resonant and near-resonant pigment vibrations suggest that photosynthetic energy transfer presents a novel design in which electronic energy transfer proceeds non-adiabatically through clusters of vibrations with frequencies distributed around electronic energy gaps. I will also briefly talk about our experiments demonstrating quantitative time-resolved measurement of \textit{absolute} number of excited state molecules. Based on these measurements, an all-optical technique that simultaneously determines concentration and extinction coefficient of an unknown sample is presented. Unlike prior analytical techniques, any requirements such as sample isolation, physical handling or in situ calibrant are eliminated allowing possible extensions towards characterizing transient chemical species. [Preview Abstract] |
Tuesday, June 9, 2015 3:00PM - 3:30PM |
C1.00003: Strongly Interacting Fermi Gases: Non-Equilibrium Dynamics and Dimensional Crossover Invited Speaker: Ariel Sommer Strongly interacting atomic Fermi gases near Feshbach resonances give access to a rich variety of phenomena in many-fermion physics and superfluidity. This flexible and microscopically well-characterized system provides a pristine platform in which to benchmark many-body theories. I will describe three experiments on gases of fermionic $^6$Li atoms. In the first experiment, we study spin transport in the return to equilibrium after a spin excitation. From the dynamics near equilibrium, we obtain spin transport coefficients over a range of temperatures and interaction strengths, and observe quantum-limited spin diffusion at unitarity. In separate experiments, we study the effect of dimensionality on the binding of pairs of fermions. We tune the system from three to two dimensions by adjusting the strength of a one-dimensional optical lattice, and measure the binding energy of fermion pairs using radio-frequency spectroscopy. In a third set of experiments, we study nonlinear excitations of a fermionic superfluid. Imprinting a phase jump on the superfluid order parameter causes a long-lived, localized density depletion that oscillates through the cloud. We measure the oscillation period and find that it corresponds to an emergent particle with an effective mass of up to several hundred times the bare mass. This excitation has been identified as a solitonic vortex that results from the decay of a planar soliton. [Preview Abstract] |
Tuesday, June 9, 2015 3:30PM - 4:00PM |
C1.00004: Laser cooling, slowing and trapping of a diatomic molecule Invited Speaker: John Barry Roughly three decades ago, laser cooling and trapping succeeded in producing ultracold ions and atoms, sparking a revolution in atomic physics and subsequently becoming workhorse techniques within the field. These techniques require a ``cycling transition," where the particle of interest is repeatedly driven by a photon into an excited electronic state and quickly decays back to the initial ground state, allowing the process to repeat. Because photon absorption transfers momentum to the particle, application of force is possible. Adjusting the geometry and frequency of the applied photons allows creation of a damping (cooling) force. Further addition of a quadrupole magnetic field allows for a restoring (trapping) force. Prior to this thesis, straightforward extension of these methods to molecules was considered a practical impossibility; electronic decays in molecules tend to populate multiple rotational and vibrational states, preventing creation of a cycling transition. While a variety of ultracold molecular species is desirable to satisfy a range of applications, the only other production method is limited to species where the constituent atoms are themselves amenable to laser cooling. For other species, a different technique is required. Here we outline the methods and experiments in which laser cooling and trapping were first applied to molecules. By careful molecule choice, by using a cooling transition that exploits selection rules, and by counteracting dark states with a magnetic field, we create a cycling transition for the diatomic molecule strontium monofluoride (SrF). We show the power of this technique by demonstrating Doppler and sub-Doppler cooling in 1-D, radiation pressure slowing and stopping of a molecular beam, and finally a 3-D magneto-optical trap (MOT). Our MOT produces the coldest trapped sample of directly-cooled molecules to date, with a temperature of T $\sim$ 2.5 mK. This method is viable for several classes of diatomic molecules with a variety of energy level configurations. This work should allow advances in a range of ultracold molecule applications, from precision measurements to quantum information and quantum simulation, to studying ultracold chemical reactions. [Preview Abstract] |
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