Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session E3: Ultracold Atoms II |
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Chair: Sergio Muniz, Georgia Institute of Technology Room: Knoxville Convention Center 301D |
Wednesday, May 17, 2006 1:30PM - 1:42PM |
E3.00001: Fermi-Bose mixtures in optical lattices: a new strongly correlated system Silke Ospelkaus-Schwarzer, Christian Ospelkaus, Kai Bongs, Klaus Sengstock Quantum degenerate mixtures of fermionic and bosonic atoms represent a new class of systems offering mixed statistics and intriguing interaction features, ranging from mean-field collapse effects to strongly correlated phases with Fermion- Boson pairs forming composite Fermions. We present experimental investigations on Fermi-Bose interactions in mixtures of $^{40} $K and $^{87}$Rb atoms in harmonic trapping potentials as well as in a 3D optical lattice. In particular we discuss the first experimental observation of a localized phase of the mixture in a 3D optical lattice. This phenomenon becomes evident in the reversible loss of visibility in the interference pattern of the bosonic component, which already takes place for a shallower lattice than needed to reach the Mott insulating phase of a comparable pure bosonic system. These measurements introduce a new system to the area of strongly correlated physics and potentially connect to polaron and disorder physics. [Preview Abstract] |
Wednesday, May 17, 2006 1:42PM - 1:54PM |
E3.00002: Dynamics of a BEC colliding with a time-dependent dipole barrier M. Siercke, C. Ellenor, R. Chang, M. Partlow, A.M. Steinberg One advantage of testing theories in cold-atom systems is that it is possible to create a wide variety of potentials, to modify them in real time, and to carry out measurements of quantities which are often impossible or very difficult to measure in other systems. We will discuss experiments involving the scattering of atoms from a Bose-Einstein condensate off of time-dependent dipole barriers. During a wavepacket collision with a repulsive barrier, there is a transient enhancement of high momentum components\footnote{A.L. Perez Prieto, S. Prouard and J.G. Muga, {\it Physical Review A} \textbf{64} 012710 (2000). } that is not seen in the classical asymptotic scattering limits. If the barrier is turned off \emph{during} the collision, one can investigate this regime of the scattering process. We will present preliminary data from the experiment and describe how the technique might be used to probe the phase profile of an expanding condensate by introducing interference between the different momentum components in the cloud. While the technique relies on negligible mean field energy left in the expanding cloud it might be used to perform state tomography on the BEC to investigate any interesting dynamics before the expansion. We will also discuss future experiments on measuring different atomic tunneling times through dipole barriers. [Preview Abstract] |
Wednesday, May 17, 2006 1:54PM - 2:06PM |
E3.00003: Atom trapping with a thin magnetic film Patrick Medley, Micah Boyd, Gretchen Campbell, Jongchul Mun, Erik Streed, Dave Pritchard, Wolfgang Ketterle We have created a $^{87}$Rb Bose-Einstein condensate in a magnetic trapping potential produced by a hard disk platter written with a periodic pattern. Cold atoms were loaded from an optical dipole trap and then cooled to BEC on the surface with radiofrequency evaporation. Breakup of the atomic cloud due to imperfections in the magnetic structure was observed at distances closer than 40 $\mu$m from the surface. Attempts to use the disk as an atom mirror showed dispersive effects after reflection. [Preview Abstract] |
Wednesday, May 17, 2006 2:06PM - 2:18PM |
E3.00004: Continuous and Pulsed Quantum Zeno Effect Erik Streed, Jongchul Mun, Micah Boyd, Gretchen Campbell, Patrick Medley, David Pritchard, Wolfgang Ketterle The quantum Zeno effect is the suppression of transitions between quantum states by frequent measurement. Oscillation between two ground hyperfine states of a magnetically trapped $^{87}$Rb Bose-Einstein condensate, externally driven at a transition rate $\omega_R$, was substantially suppressed by destructively measuring one of the levels with resonant optical scattering. While an ideal continuous measurement will stop the transition, any real measurement method will occur at a finite rate. The suppression of the transition rate in the two level system was quantified for pulsed measurements with a time between pulses $\delta t$ and weak continuous measurements with a scattering rate $\gamma$. We observe that the weak continuous measurements exhibit the same suppression in the transition rate as the pulsed measurements when $\gamma\delta t=3.60(0.43)$, in agreement with the previously predicted value of 4. Increasing the measurement frequency suppressed the transition rate down to $0.005\omega_R$. [Preview Abstract] |
Wednesday, May 17, 2006 2:18PM - 2:30PM |
E3.00005: Bose-Einstein condensates in a rotating lattice Lincoln D. Carr, Rajiv Bhat, Murray J. Holland Strongly interacting bosons in two dimensions in a rotating square lattice are investigated via a modified Bose-Hubbard Hamiltonian. Such a system corresponds to a rotating lattice potential imprinted on a trapped Bose-Einstein condensate. Second-order quantum phase transitions between states of different symmetries are observed at discrete rotation rates, depending on the lattice filling factor. These rotational quantum phases correspond to increasing numbers of vortices packed on the lattice. [Preview Abstract] |
Wednesday, May 17, 2006 2:30PM - 2:42PM |
E3.00006: Two-Qubit Motional Gates in Double-Well Optical Lattices Mark Edwards, James Porto, Charles W. Clark A controllable, phase-stable two-dimensional array of double- well optical potentials can be created by crossing two pairs of counterpropagating laser beams. If such a lattice is applied to a gaseous Bose-Einstein condensate and the depth of the lattice is ramped up, it is possible to ``freeze'' exactly two atoms at the site of each double-well potential. The relative depths of the wells of the potential can be controlled along with the height of the central barrier by applying a phase shift to one of the pairs of counterpropagating beams. We are, therefore, able to adjust the potential so that there are two distinguishable motional states of a single atom on each side of the double-well potential. These pairs of motional states can then be used as qubit states. We have studied the quantum dynamics of two interacting particles moving in this adjustable double-well potential. All of the dynamics can be understood using three separate few-state models (for sufficiently wide band-gap energy spectra) whose individual dynamics can be well understood using Landau-Zener theory. We present these models and analyze the behavior of the two atoms for several different time-dependent changes of the double-well potential. The suitability of these dynamical changes in serving as a two-qubit quantum gate are assessed. [Preview Abstract] |
Wednesday, May 17, 2006 2:42PM - 2:54PM |
E3.00007: Observation of Strong Quantum Depletion in a Gaseous Bose-Einstein Condensate Yingmei Liu, Kaiwen Xu, Daniel Miller, JitKee Chin, Widagdo Setiawan, Wolfgang Ketterle We studied quantum depletion in a gaseous Bose-Einstein condensate. An optical lattice enhanced the atomic interactions and modified the dispersion relation resulting in strong quantum depletion. The depleted fraction was directly observed as a diffuse background in the time-of-flight images. Bogoliubov theory provided a semi-quantitative description for our observations of depleted fractions in excess of $50\%$. [Preview Abstract] |
Wednesday, May 17, 2006 2:54PM - 3:06PM |
E3.00008: The role of interactions, tunneling and harmonic confinement on the adiabatic loading of bosons in an optical lattice. Ana Maria Rey, Guido Pupillo, Trey Porto Cold atoms in optical lattices provide a system for realizing interacting many-body systems in essentially defect free lattices. Lattice-based systems are typically governed by three energy scales: interaction U, tunneling J and the temperature. In atomic systems, the energies U and J can be controlled by adjusting the lattice parameters, however, unlike condensed matter systems, it is experimentally difficult to measure very low temperatures. Absent good thermometers it is important to understand the thermodynamics of experimentally realistic systems. I will present entropy-temperature curves for interacting bosons in unit filled lattices for both homogeneous and harmonically trapped situations, and use them to understand how adiabatic changes in the lattice depth affect the temperature of the system. I will show that in the homogeneous case, unlike the non-interacting bosonic system which is always cooled upon adiabatic loading for low enough initial temperature, the change in the excitation spectrum induced by interactions can lead to heating. On the other hand the presence of the parabolic confinement can significantly reduce the final available temperature, due to the non-vanishing superfluid component at the edge of the cloud in trapped systems. [Preview Abstract] |
Wednesday, May 17, 2006 3:06PM - 3:18PM |
E3.00009: Laser cooling and localization measurements in a Raman optical lattice Rachel Sapiro, Rui Zhang, Natalya Morrow, Paul Berman, Georg Raithel Recently, a new type of optical lattice, referred to as a Raman optical lattice, has been demonstrated. In one-dimensional implementations, the Raman optical lattice is formed by four laser beams and has a basic periodicity of $\lambda/4$, which is a factor of two less than in conventional optical lattices. Since the Raman lattice supports a novel sub-Doppler cooling mechanism, atoms can be cooled and localized in the wells of the lattice. In this work, we use time-of-flight temperature measurements to study the dependence of the cooling efficiency on the detuning parameters of the system. Furthermore, an optical-mask technique is employed to measure the atomic-density distribution in the lattice. The technique is first tested in a two-beam lattice configuration that yields an atomic-density distribution with $\lambda/2$ periodicity (in this test lattice, magnetic-field-induced laser cooling is effective). We then use the mask technique to obtain preliminary evidence of the $\lambda/4$ periodicity of the atomic-density distribution in the Raman lattice. [Preview Abstract] |
Wednesday, May 17, 2006 3:18PM - 3:30PM |
E3.00010: Vidal’s simulation method applied to two coupled 1D lattices Jamie Williams, Ippei Danshita, Charles Clark Recently, a method was developed employing matrix product states to simulate the quantum dynamics of a one dimensional lattice system using an adaptive time stepping technique [G. Vidal, Phys. Rev. Lett. 91, 147902 (1993); Phys. Rev. Lett. 93, 040502 (1994)]. We use this approach to simulate the dynamics of bosons loaded into a double-well optical lattice geometry relevant to recent experiments at NIST [I. Spielman et al., Bull. Am. Phys. Soc. (2005)]. We study a pair of coupled 1D lattices, which can be mapped into a single 1D lattice with next-nearest neighbor interactions. [Preview Abstract] |
Wednesday, May 17, 2006 3:30PM - 3:42PM |
E3.00011: Parametric Amplification of Scattered Atom Pairs Gretchen K. Campbell, Jongchul Mun, Micah Boyd, Erik W. Streed, Wolfgang Ketterle, David E. Pritchard We have observed parametric generation and amplification of ultracold atom pairs. A $^{87}$Rb Bose-Einstein condensate was loaded into a one-dimensional optical lattice with quasimomentum $k_{0}$ and spontaneously scattered into two final states with quasimomenta $k_{1}$ and $k_{2}$ . Furthermore, when a seed of atoms was first created with quasimomentum $k_{1}$ we observed parametric amplification of scattered atoms pairs in states $k_{1}$ and $k_{2}$ when the phase-matching condition was fulfilled. This process is analogous to optical parametric generation (OPG) and amplification (OPA) of photons and could be used to efficiently create entangled pairs of atoms. Furthermore, these results could explain the dynamic instability of condensates in moving lattices observed in recent experiments. [Preview Abstract] |
Wednesday, May 17, 2006 3:42PM - 3:54PM |
E3.00012: Dispersion Management Using Betatron Resonances in an Ultracold-Atom Storage Ring Kater Murch, Kevin Moore, Subhadeep Gupta, Dan Stamper-Kurn Particles circulating at specific velocities in a storage ring can undergo betatron resonances at which static perturbations of the particles' orbit yield large transverse (betatron) oscillations. We have observed betatron resonances in an ultracold atom storage ring and found these resonances to cause the near elimination of the longitudinal dispersion of atomic beams propagating at resonant velocities. This effect can improve atom-interferometric devices. Both the resonant velocities and the resonance strengths were varied by deliberate modifications to the storage ring. [Preview Abstract] |
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