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 P6: Cooling Methods and Interacting BEC's |
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Chair: Logan Clark, University of Chicago Room: 552AB |
Thursday, May 26, 2016 2:00PM - 2:12PM |
P6.00001: Cooling a degenerate Fermi gas in an optical trap by parametric excitation with anharmonic trapping frequency Jiaming Li, Ji Liu, Leonardo de Melo, Le Luo We demonstrate a technique for parametric cooling a degenerate Fermi gas in a crossed-beam optical trap, where high-energy atoms near the trap edge can be selectively removed by modulating the stiffness of the potential with anharmonic trapping frequencies [1]. A noninteracting degenerate Fermi gas is used for a proof of principle study, in which other cooling mechanisms are minimized and the excited high-energy atoms can leave the trap quickly without colliding with the low-energy atoms. We apply the parametric excitation by modulating the optical intensity of the trapping beams and measure the dependence of the cloud energy on the frequency and amplitude of the modulation. It is found that large anharmonicity along the axial trapping potential allows to generate anisotropic energy distribution, in which the axial cloud energy can be reduced to the ground state value when the modulation frequency is tuned to resonance with anharmonic trapping frequency. After cross-dimensional thermalization, the equipartition energy distribution is retrieved and the energy per particle $E/E_F$ decreases about $20\%$. [1] Jiaming Li, Ji Liu, Wen Xu, Leonardo de Melo, Le Luo, arXiv:1512.01277 (2015). [Preview Abstract] |
Thursday, May 26, 2016 2:12PM - 2:24PM |
P6.00002: Supercooling of Atoms in an Optical Resonator Minghui Xu, Simon J\"ager, Stefan Sch\"utz, John Cooper, Giovanna Morigi, Murray Holland We investigate laser cooling of an ensemble of atoms in an optical cavity. We demonstrate that when atomic dipoles are synchronized in the regime of steady-state superradiance, the motion of the atoms may be subject to a giant frictional force leading to potentially very low temperatures. The ultimate temperature limits are determined by a modified atomic linewidth, which can be orders of magnitude smaller than the cavity linewidth. The cooling rate is enhanced by the superradiant emission into the cavity mode allowing reasonable cooling rates even for dipolar transitions with ultranarrow linewidth. [Preview Abstract] |
Thursday, May 26, 2016 2:24PM - 2:36PM |
P6.00003: The Cold Atom Laboratory: a facility for ultracold atom experiments aboard the International Space Station David Aveline Spread across the globe there are many different experiments in cold quantum gases, enabling the creation and study of novel states of matter, as well as some of the most accurate inertial sensors currently known. The Cold Atom Laboratory (CAL), being built at NASA's Jet Propulsion Laboratory (JPL), will be a multi-user facility that will allow the first study of ultracold quantum gases in the microgravity conditions of the International Space Station (ISS). The microgravity environment offers a wealth of advantages for studies of cold atoms, including expansion into extremely weak traps and achieving unearthly cold temperatures. It will also enable very long interaction times with released samples, thereby enhancing the sensitivity of cold atom interferometry. We will describe the CAL mission objectives and the flight hardware architecture. We will also report our ongoing technology development for the CAL mission, including the first microwave evaporation to Bose-Einstein condensation (BEC) on a miniaturized atom chip system, demonstrated in JPL's CAL Ground Testbed. We will present the design, setup, and operation of two experiments that reliably generate and probe BECs and dual-species mixtures of Rb-87 and K-39 (or K-41). CAL is scheduled to launch to the ISS in 2017. The CAL mission is supported by NASA's SLPS and ISS-PO. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. [Preview Abstract] |
Thursday, May 26, 2016 2:36PM - 2:48PM |
P6.00004: Rapid Cooling to Quantum Degeneracy in Dynamically Shaped Atom Traps Richard Roy, Alaina Green, Ryan Bowler, Subhadeep Gupta We report on a general method for the rapid production of quantum degenerate gases. Using $^{174}$Yb, we achieve an experimental cycle time as low as $(1.6\!-\!1.8)\,$s for the production of Bose-Einstein condensates (BECs) of $(0.5\!-\!1)\!\times\!10^5$ atoms. While laser cooling to $30\,\mu$K proceeds in a standard way, evaporative cooling is highly optimized by performing it in an optical trap that is dynamically shaped by utilizing the time-averaged potential of a single laser beam moving rapidly in one dimension. We also produce large ($>\!10^6$) atom number BECs and successfully model the evaporation dynamics over more than three orders of magnitude in phase space density. Our method provides a simple and general approach to solving the problem of long production times of quantum degenerate gases. [Preview Abstract] |
Thursday, May 26, 2016 2:48PM - 3:00PM |
P6.00005: A 3-photon process for producing degenerate gases of metastable alkaline-earth atoms Daniel S. Barker, Neal C. Pisenti, Benjamin J. Reschovsky, Gretchen K. Campbell We present a method for creating quantum degenerate gases of metastable alkaline-earth atoms. A degenerate gas in any of the $^{3}P$ metastable states has not previously been obtained due to large inelastic collision rates, which are unfavorable for evaporative cooling. Samples prepared in the $^{1}S_{0}$ ground state can be rapidly transferred to either the $^{3}P_{2}$ or $^{3}P_{0}$ state via a coherent 3-photon process. Numerical integration of the density matrix evolution for the fine structure of bosonic alkaline-earth atoms shows that transfer efficiencies of $\simeq90\%$ can be achieved with experimentally feasible laser parameters in both Sr and Yb. Importantly, the 3-photon process does not impart momentum to the degenerate gas during excitation, which allows studies of these metastable samples outside the Lamb-Dicke regime. We discuss several experimental challenges to the successful realization of our scheme, including the minimization of differential AC Stark shifts between the four states connected by the 3-photon transition. [Preview Abstract] |
Thursday, May 26, 2016 3:00PM - 3:12PM |
P6.00006: Universal, non-monotonic structure in the saturation curves of a linear Paul trap James Wells, Jonathan Kwolek, Douglas Goodman, Reinhold Blümel, Winthrop Smith A common technique to measure ion-atom collision rates in a hybrid trap if the ions have no optical transitions (e.g. alkalis) is to monitor the fluorescence of the neutrals in the presence of a saturated linear Paul trap (LPT) [1]. We present numerical simulations, analytical calculations, and experimental results that show that the steady-state ion capacity of an LPT, $N_s$, exhibits nonlinear, nonmonotonic behavior as a function of ion loading rate, $\Lambda$ [2]. The steady state as a function of loading rate, $N_s(\Lambda)$, shows four distinct regions. In Region I, at the lowest $\Lambda$, $N_s(\Lambda)$ increases monotonically. Then, $N_s(\Lambda)$ reaches a plateau in Region II, before decreasing to a local minimum in Region III. Finally, in Region IV, $N_s(\Lambda)$ once again increases monotonically. This behavior appears universal to any Paul trap, regardless of geometry or species trapped. We examine this behavior experimentally as a function of the $q$ stability parameter of the Paul trap and simulate numerically the effect of the particular trap geometry on the onset of each of the four regions. \\ \noindent [1] Goodman, et al. PRA {\bf 91}, 012709 (2015) and Lee, et al. PRA {\bf 87}, 052701 (2013)\\ \noindent [2] Bl\"{u}mel, et al. PRA {\bf 92}, 063402 (2015) [Preview Abstract] |
Thursday, May 26, 2016 3:12PM - 3:24PM |
P6.00007: Two-body correlations and natural-orbital tomography in ultracold bosonic systems of definite parity Sven Kroenke, Peter Schmelcher Deep insights into the structure of a many-body state can often be inferred from its natural orbitals (eigenvectors of the reduced one-body density operator) and their populations. These quantities allow e.g.\ to distinguish a Bose-Einstein condensate from a correlated many-body state [1] and were utilized to understand many-body processes such as the decay of dark solitons due to dynamical quantum depletion [2].\\ We explore the relationship between natural orbitals, one-body coherences and two-body correlations for a certain important class of bosonic many-body wave-functions with definite parity [3]. The strength of two-body correlations at the parity-symmetry center is shown (i) to characterize the number state distribution and (ii) to control the structure of non-local two-body correlations. A recipe for the experimental reconstruction of the natural-orbital densities based on two-body correlation measurements is derived. These results are applied to decaying dark solitons.\newline [1] O.\ Penrose, L.\ Onsager. {\it Phys. Rev.} {\bf 104}, 576 (1956). [2] R.\ V.\ Mishmash et al. {\it Phys. Rev. A} {\bf 80}, 053612 (2009); S.\ Kr\"onke, P.\ Schmelcher. {\it Phys. Rev. A} {\bf 91}, 053614 (2015). [3] S.\ Kr\"onke, P.\ Schmelcher. {\it Phys. Rev. A} {\bf 92}, 023631 (2015). [Preview Abstract] |
Thursday, May 26, 2016 3:24PM - 3:36PM |
P6.00008: Convex Decompositions of Thermal Equilibrium for Non-interacting Non-relativistic Particles Aurelia Chenu, Agata Branczyk, John Sipe We provide convex decompositions of thermal equilibrium for non-interacting non-relativistic particles in terms of localized wave packets. These quantum representations offer a new tool and provide insights that can help relate to the classical picture. Considering that thermal states are ubiquitous in a wide diversity of fields, studying different convex decompositions of the canonical ensemble is an interesting problem by itself. The usual classical and quantum pictures of thermal equilibrium of $N$ non-interacting, non-relativistic particles in a box of volume $V$ are quite different. The picture in classical statistical mechanics is about (localized) particles with a range of positions and velocities; in quantum statistical mechanics, one considers the particles (bosons or fermions) associated with energy eigenstates that are delocalized through the whole box. Here we provide a representation of thermal equilibrium in quantum statistical mechanics involving wave packets with a localized coordinate representation and an expectation value of velocity. In addition to derive a formalism that may help simplify particular calculations, our results can be expected to provide insights into the transition from quantum to classical features of the fully quantum thermal state. [Preview Abstract] |
Thursday, May 26, 2016 3:36PM - 3:48PM |
P6.00009: Cavity Control and Cooling of Nanoparticles in High Vacuum James Millen Levitated systems are a fascinating addition to the world of optically-controlled mechanical resonators. It is predicted that nanoparticles can be cooled to their c.o.m. ground state via the interaction with an optical cavity\footnote{T S Monteiro et al., \textbf{New J. Phys. 15} (2013)}. By freeing the oscillator from clamping forces dissipation and decoherence is greatly reduced, leading to the potential to produce long-lived, macroscopically spread, mechanical quantum states, allowing tests of collapse models and any mass limit of quantum physics. Reaching the low pressures required to cavity-cool to the ground state has proved challenging\footnote{\textbf{JM} et al., \textbf{Nature Nanotechnology 9}, 425 (2014)}. Our approach is to cavity cool a beam of nanoparticles in high vacuum. We can cool the c.o.m. motion of nanospheres\footnote{P Asenbaum, et al., \textbf{Nature Communications 4}, (2013)}, and control the rotation of nanorods\footnote{S Kuhn et al., \textbf{Nano Letters 15}, (2015)}, with the potential to produce cold, aligned nanostructures. Looking forward, we will utilize novel microcavities to enhance optomechanical cooling, preparing particles in a coherent beam ideally suited to ultra-high mass interferometry at $10^7$ a.m.u. [Preview Abstract] |
Thursday, May 26, 2016 3:48PM - 4:00PM |
P6.00010: Enhanced Magnetic Trap Loading for Alkaline-Earth Atoms Benjamin J. Reschovsky, Daniel S. Barker, Neal C. Pisenti, Gretchen K. Campbell We report on a technique to improve the continuous loading of atomic strontium into a magnetic trap from a Magneto-Optical Trap (MOT). This is achieved by adding a depumping laser addressing the $^3P_1$ level. For the $^3P_1 \rightarrow \ ^3S_1$ (688-nm) transition in strontium, the depumping laser increases atom number in the magnetic trap and subsequent cooling stages by up to $65~\%$ for the bosonic isotopes and up to $30~\%$ for the fermionic isotope. We optimize this trap loading strategy with respect to the 688-nm laser detuning, intensity, and beam size. To understand the results, we develop a one-dimensional rate equation model of the system, which is in good agreement with the data. We discuss the use of other transitions in strontium for accelerated trap loading and the application of the technique to other alkaline-earth-like atoms. [Preview Abstract] |
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