Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session K4: Experiments with Cold and Ultracold Atoms |
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Chair: Doerte Blume, Washington State University Room: Nittany Lion Inn Ballroom AB |
Thursday, May 29, 2008 2:00PM - 2:12PM |
K4.00001: Atom-molecule oscillations in a Bose-Fermi mixture. M.L. Olsen, J.D. Perreault, T.D. Cumby, D.S. Jin We will discuss experiments in which we create a coherent superposition of atom and molecule states in an ultracold gas mixture of $^{87}$Rb and $^{40}$K atoms. Using rapid magnetic-field pulses near an interspecies Feshbach resonance, we couple atoms and heteronuclear molecules. Rabi- and Ramsey-type experiments yield atom-molecule oscillations with relatively large contrast and coherence times up to several hundred microseconds. [Preview Abstract] |
Thursday, May 29, 2008 2:12PM - 2:24PM |
K4.00002: Stable mixtures of $^6$Li fermions in the three lowest energy spin states J.R. Williams, J.H. Huckans, R.W. Stites, E.L. Hazlett, K.M. O'Hara Studies of strongly interacting $^6$Li Fermi gases have focused exclusively on mixtures of atoms in the two lowest energy hyperfine states (states $|1\rangle$ and $|2\rangle$ which correspond to the states $\left|F=1/2,m_F = \pm 1/2\right\rangle$ at zero field). Here we investigate mixtures of $^6$Li atoms that include population in state $|3\rangle$ (corresponding to the $\left|F = 3/2,m_F = -3/2\right\rangle$ state at zero field). Mixtures of $^6$Li atoms in states $|1\rangle, |2\rangle$ and $|3\rangle$ have several interesting features. Feshbach resonances occur in collisions between any two of these three states. Notably, a broad $|1\rangle - |3\rangle$ Feshbach resonance is predicted to occur at a significantly lower field (690 Gauss) compared to the broad $|1\rangle - |2\rangle$ and $|2\rangle - |3\rangle$ Feshbach resonances (at 834 G and 811 G respectively). Furthermore, at high magnetic fields the $|1\rangle - |3\rangle$ and $|2\rangle - |3\rangle$ mixtures only have a weak two-body decay channel via spin-dipole coupling. Finally, the energy of states $|1\rangle, |2\rangle$ and $|3\rangle$ tune at approximately the same rate as a function of magnetic field. We will report on our measurements of inelastic loss rates for these mixtures and useful applications for these three states in quantum information processing and investigations of the repulsive Hubbard model. [Preview Abstract] |
Thursday, May 29, 2008 2:24PM - 2:36PM |
K4.00003: Progress Towards a Quantum Gas Microscope Jonathon Gillen, Waseem Bakr, Amy Peng, Simon Foelling, Markus Greiner We will present the latest progress towards a quantum gas microscope to experimentally realize and study complex many-body systems realized with a BEC of rubidium in an optical lattice. The experiment should allow us to achieve sub-micron optical resolution. Such imaging enables single atom sensitivity and optical resolutions on the order of the lattice spacing. The high resolution optics also enables flexible preparation of quantum states as well as the generation of arbitrarily shaped potentials. [Preview Abstract] |
Thursday, May 29, 2008 2:36PM - 2:48PM |
K4.00004: Progress Towards a Dual BEC of Na Rb. Gustavo Telles, Matthew Gibbs, Andrew Seltzman, Chandra Raman We report on the status of a dual species atomic Bose-Einstein condensate of $^{23}$Na and $^{87}$Rb. Our apparatus has been specially built to investigate the collisional dynamics and properties of this unique mixture of alkali metal atoms, including kilogauss magnetic field capability and high optical access. Our approach incorporates a Zeeman slower capable of delivering a large flux of both Na and Rb, magneto-optical trapping of both species, capturing and cooling of large ($\sim $10$^{10})$ numbers of $^{23}$Na atoms to sympathetically cool $^{87}$Rb. We are also interested in probing the heteronuclear Feshbach resonances in the ultracold mixture. The eventual goal is to synthesize and manipulate heteronuclear ultracold dimer molecules. Future experiments and ideas will be discussed. [Preview Abstract] |
Thursday, May 29, 2008 2:48PM - 3:00PM |
K4.00005: A Pumped Atom Laser John Close, Nick Robins, Cristina Figl, Matthew Jeppesen, Graham Dennis We have experimentally demonstrated simultaneous pumping and out-coupling of an atom laser via Bose enhanced (by the condensate) spontaneous photon emission. Source atoms in the $\vert $F = 2, M$_{F }$= 0$>$ hyperfine state of $^{87}$Rb are coupled by a light field to the $\vert $F ' = 1, M$_{F}$ = 0$>$ excited state and are then stimulated to emit a photon by \underline {atoms} already in the $\vert $F = 1, M$_{F }$= -1$>$ lasing (condensate) mode. The source atoms enter the $\vert $F = 1, M$_{F }$= -1$>$ condensate, pumping the laser mode. Atoms are simultaneously RF out-coupled from the $\vert $F = 1, M$_{F }$= -1$>$ condensate to produce an atom laser beam. The pumping process is stimulated, preserving the phase of the lasing mode, is irreversible and is compatible with an atom delivery system to replenish the source atoms. Many of the properties that make \textit{optical} lasers useful are gained through simultaneous out-coupling and pumping producing a narrow line-width continuous beam. The same can be expected for an atom laser. We present the data from the pumping experiment, and compare it with a rate equation model. [Preview Abstract] |
Thursday, May 29, 2008 3:00PM - 3:12PM |
K4.00006: Properties of Magnetic Sublevel Coherences for Precision Measurements Iain Chan, A. Kumarakrishnan We have developed a theoretical description of the evolution of ground state coherences between magnetic sublevels in Rb vapor in the presence of a magnetic field along an arbitrary direction. This formalism uses a rotation matrix approach to describe the evolution of coherences created by two traveling wave laser pulses with orthogonal polarizations. The effect of a magnetic field can be described as a time dependent rotation of the atomic system about the quantization axis. Predictions based on this approach are shown to agree with experiments. By using rate equations to model atomic coherences, it is also possible to predict the evolution of coherence grating echoes in a magnetic field. Echoes are realized by rephasing the coherences using a second set of traveling wave pulses. The two sets of traveling wave pulses are separated by t = T so that the effect of Doppler dephasing is eliminated at t = 2T resulting in the formation of an echo. Applications relating to precision measurements of atomic g factor ratios are considered. [Preview Abstract] |
Thursday, May 29, 2008 3:12PM - 3:24PM |
K4.00007: Studying decoherence of cold atoms in optical lattices through 2D pump-probe spectroscopy Samansa Maneshi, Chao Zhuang, XiaoXian Liu, Luciano Cruz, Aephraim Steinberg We study the quantized centre-of-mass motion of 85Rb atoms trapped in a 1D optical lattice. We have measured the coherence between the quantum vibrational states of the atoms in the lattice wells, and using pulse echo observe a striking ``fidelity freeze'' which has never before been observed in such systems.~Pump-probe spectroscopy provides information about the temporal correlation properties of the instantaneous well depth experienced by the atoms as they drift through a spatially inhomogeneous lattice. In the 1D lattice, atoms are free to move in the transverse plane with their average transverse velocity. Our pump and probe pulses consist of sinusoidal spatial translations of the lattice. Our experimental data show a frequency drift towards lower values as we increase the time between the pump and probe pulses. This is consistent with the transverse expansion of atoms. We study the effect of transverse confinement (a 3D lattice) and different cloud parameters on the echo decay and on the 2D pump-probe spectra, in order to elucidate the connection between transverse motion, frequency correlation time, and decoherence. [Preview Abstract] |
Thursday, May 29, 2008 3:24PM - 3:36PM |
K4.00008: Using Spin Echo Techniques to Measure and Null Background Magnetic Fields in Cold Atom Experiments Aaron Smith Quantum control of atomic spins requires precise control of the total magnetic field acting on the spins. This makes accurate nulling of the (generally time dependent) background magnetic field one of the most important limiting factors of a real-world control experiment. We have devised a convenient method to use the atoms themselves as an in situ probe, combining spin-echo techniques and polarization spectroscopy to generate a highly sensitive signature of a desired component of the field. This allows us to quickly and independently measure three orthogonal components of the total field with a resolution of a few tens of $\mu $G in a bandwidth of $\sim $1kHz, and to apply the inverse of the measured field with three sets of Helmholtz coils driven by arbitrary waveform generators. The resulting background field is typically less than $\sim $50$\mu $G rms averaged over a 10 ms window, an overall reduction of about one order of magnitude compared to the uncompensated AC field in our laboratory. [Preview Abstract] |
Thursday, May 29, 2008 3:36PM - 3:48PM |
K4.00009: Faraday Spectroscopy of Atoms Confined in a Dark Optical Trap Matthew Terraciano, Spencer Olson, Mark Bashkansky, Fredrik Fatemi We demonstrate sensitive Faraday spectroscopy with atoms confined in dark optical traps. Atoms in blue-detuned traps are confined to regions of darkness, dramatically reducing off-resonant photon scattering and light shifts compared to red-detuned traps. We use this technique to continuously sample time-varying magnetic fields with minimal trap-induced dephasing. A hollow laser beam, formed by a spatial light modulator, is crossed in a bow-tie configuration and is loaded from a $^{85}$Rb MOT. Trapped atoms are continuously probed with a linearly-polarized off-resonant ($\Delta $ = -3 GHz) beam which is monitored with a polarimeter to detect the Larmor precession. The sample is spin polarized every 1-2 ms allowing for continuous sampling of the magnetic field for 400 ms in a signal shot. We present the ability of this technique to measure various time-varying fields with $\sim $10 $\mu $G resolution as well as to compensate for unwanted magnetic field fluctuations (eddy currents, ambient AC line noise). [Preview Abstract] |
Thursday, May 29, 2008 3:48PM - 4:00PM |
K4.00010: Imaging velocity selective resonances in a magnetic field Fredrik Fatemi, Matthew Terraciano, Mark Bashkansky, Zachary Dutton We demonstrate a simple technique for single-shot imaging of a magnetic field using stimulated Raman transitions. Freely expanding cold atoms released from a magneto-optical trap are exposed to a brief ($\sim $1 msec) retro-reflected laser pulse in a lin-perp-lin configuration detuned a few GHz from resonance. Because the two-photon resonance condition is satisfied only for narrow velocity classes, most atoms continue freely expanding. In contrast, the momentum of resonant atoms is altered by the pulse, and this two-photon momentum change is easily visible after further ballistic expansion. When the momentum pulse is applied to an atom cloud with finite size, magnetic field variations across the sample result in position-dependent features in images of the expanded cloud. Furthermore, when the stimulated Raman transitions occur between different hyperfine ground states, the resonance condition is dependent on the initial magnetic sublevel quantum number. We have used this technique for single-shot imaging of magnetic sublevel distributions. [Preview Abstract] |
Thursday, May 29, 2008 4:00PM - 4:12PM |
K4.00011: Study of size-dependent interaction in driven cold atomic system Myoung-Sun Heo, Yonghee Kim, Wonho Jhe, Heung-Ryoul Noh It is well known that there exist cooperative interactions between magneto-optically trapped cold atoms, which is considered as a barrier to highly correlated quantum gases. However under some conditions, this can serve for adjustable interactions between atoms. When atoms are driven periodically, their one-dimensional motions can make effective global attractive interaction leading to spontaneous symmetry breaking (SSB) of atomic population on two symmetric attractors generated by parametric resonance. Here we have experimentally elucidated the effect of interaction in terms of thermodynamic response of atoms to the variation of system size, or total number of atoms, and bias field. In the regime of static response to the variation of system size, we have found that this SSB lies in the same universality class as mean-field Ising phase transition. When the oscillating bias field is exerted, the hysteric response of the system changes drastically over the critical number of atoms. [Preview Abstract] |
Thursday, May 29, 2008 4:12PM - 4:24PM |
K4.00012: ATTA-3: The Next-Generation Instrument for $^{81}$Kr-Dating Yun Ding, Z.-T. Lu, K. Bailey, P. Mueller, T.P. O'Connor, R.W. Dunford, L. Young, A.M. Davis , N.C. Sturchio , W. Jiang, S.-M. Hu Atom Trap Trace Analysis (ATTA) has been used to analyze two rare isotopes: $^{81}$Kr (half-life = 230,000 yr, isotopic abundance $\sim $ 10$^{-12})$ and $^{85}$Kr ($\sim $10$^{-11})$, in environmental samples. Radiokrypton dating enabled by the ATTA method can now be used to determine the ages of old groundwater in the range of 50,000--1,000,000 years. The present apparatus (ATTA-2) has an overall counting efficiency of 0.01{\%} and, for $^{81}$Kr dating, requires a water sample of at least 1,000 liters. We are developing a new apparatus (ATTA-3) to trap and count $^{81}$Kr atoms with the goal of reaching a counting efficiency of 1{\%}. The required sample size could be reduced down to 10 liters of water or ice. ATTA-3 would enable a wide range of applications in the earth sciences. This work is supported by NSF, Division of Earth Sciences, under Award No. EAR-0651161, and by DOE, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 [Preview Abstract] |
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