Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session S5: Ultracold Mixtures / Lattices |
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Chair: Kirk Madison, University of British Columbia Room: Arboretum I-III |
Friday, May 28, 2010 2:00PM - 2:12PM |
S5.00001: A trapped single ion inside a Bose-Einstein condensate Carlo Sias, Christoph Zipkes, Stefan Palzer, Michael Koehl The achievement of excellent control of the motional and the internal quantum states of ultracold neutral atoms and ions has opened intriguing possibilities for quantum simulation and quantum computation. Until now quantum gases and single trapped ions have been disconnected in experiments. Their complementarity suggests, however, that they could be advantageously combined into one hybrid system. In our experiment, we explore the immersion of a single trapped $^{174}$Yb$^{+}$ ion into a Bose-Einstein condensate of $^{87}$Rb neutral atoms. We demonstrate the independent control over the two systems, study the fundamental interaction processes, and observe sympathetic cooling of a single ion by immersion into a Bose-Einstein condensate. Our experiment opens possibilities for continuous cooling of a quantum computer and for exploring entanglement in hybrid quantum systems. Moreover, it will pave the way for fundamental studies of decoherence of a single locally controlled impurity particle coupled to a quantum environment. [Preview Abstract] |
Friday, May 28, 2010 2:12PM - 2:24PM |
S5.00002: Quantum degeneracy of mixed strontium gases Mi Yan, Brian DeSalvo, Pascal Mickelson, Natali Martinez de Escobar, Thomas Killian We have attained quantum degeneracy in a mixture of $^{88}$Sr (bosons) and $^{87}$Sr (fermions). A Bose-Einstein condensate of $^{88}$Sr, which has attractive interactions, is produced via sympathetic cooling using $^{87}$Sr.~Simultaneously, we have demonstrated Fermi degeneracy of $^{87}$Sr by observing the difference in the sizes of the atom cloud, due to the Fermi pressure, between degenerate $^{87}$Sr and $^{88}$Sr. [Preview Abstract] |
Friday, May 28, 2010 2:24PM - 2:36PM |
S5.00003: Local probing and thermometry of a degenerate Fermi gas Torben M\"{u}ller, Bruno Zimmermann, Jakob Meineke, David Stadler, Jean-Philippe Brantut, Henning Moritz, Tilman Esslinger Ultracold atomic gases are ideal systems to study many-body quantum physics. The development of increasingly sophisticated experimental probes now starts to give direct, \emph{in-situ} access to thermodynamic quantities of these systems. We have set up a new apparatus that allows local probing of a degenerate Fermi gas with an optical resolution of $700$ nm using a microscope objective. In this talk we will present results obtained by studying \emph{in-situ} atom number fluctuations of an optically trapped gas of degenerate $^6$Li atoms. In particular, we will discuss the experimental realization of an universal scheme for thermometry recently proposed by Q. Zhou and T.-L. Ho [arXiv:0908.3015v2]. [Preview Abstract] |
Friday, May 28, 2010 2:36PM - 2:48PM |
S5.00004: Linear response thermometry with ultracold fermionic atoms in an optical lattice Daniel Greif, Leticia Tarruell, Thomas Uehlinger, Robert Jordens, Niels Strohmaier, Henning Moritz, Tilman Esslinger The low-temperature Fermi-Hubbard model is expected to capture many fascinating phenomena such as d-wave superfluidity. In our experiment we use a repulsive two-component Fermi gas loaded into a 3D optical lattice to realize this simple model Hamiltonian. Currently several experiments are reaching out to achieve even lower temperatures with novel cooling schemes in order to access and characterize the magnetically ordered state. This requires a temperature sensitive probe in the lattice. We show how linear response to weak lattice modulation can be used as a thermometer in the lattice. This can also be employed as a detector for local spin ordering. [Preview Abstract] |
Friday, May 28, 2010 2:48PM - 3:00PM |
S5.00005: A degenerate gas of Fermi atoms in a 1D optical lattice Andrey Turlapov, Kirill Martiyanov, Vasiliy Makhalov We have prepared a gas of Fermi atoms trapped in the anti-nodes of a standing electromagnetic wave. The standing wave is created by 2 counterpropagating beams, which are focused on the same spot and have a wavelength of 10.6 microns. Each cell of the potential confines a disc-shape clouds of 8000 atoms of lithium-6 in 2 equally populated spin-states with the temperature $T<0.1E_F$, where $E_F$ is the Fermi energy. Due to the large period of the lattice, the density profile in each cell is imaged directly. The system is in the regime violating the local density approximation: Only the 3 lowest levels of the axial potential are populated. This experimental system may be used to study quasi-2D Fermi physics. [Preview Abstract] |
Friday, May 28, 2010 3:00PM - 3:12PM |
S5.00006: Toward Simultaneous Quantum Degeneracy of $^{133}$Cs and $^6$Li Atoms Arjun Sharma, Skyler Degenkolb, Nathan Gemelke, Kathy-Anne Brickman Soderberg, Cheng Chin A quantum degenerate mixture of $^{133}$Cs and $^6$Li atoms provides interesting prospects to investigate few- and many-body physics and to realize quantum information processing. Simultaneous evaporative cooling of bosonic $^{133}$Cs and fermionic $^6$Li is challenging. In an optical dipole trap formed with a 1064nm laser, $^{133}$Cs (resonant transition at 852nm) experiences a deeper potential than $^6$Li (at 671nm). Since laser cooling allows a much lower initial temperature for $^{133}$Cs (10$\mu$K) than for $^6$Li (150$\mu$K), a wide, shallow trap optimizes $^{133}$Cs loading, but $^6$Li requires a deep trap. Efficient cooling of $^6$Li involves Feshbach resonance tuning near 800G, but $^{133}$Cs collision properties are untested at high fields. Furthermore, sympathetic cooling of $^6$Li by $^{133}$Cs can suffer from the large mass ratio causing imperfect overlap of clouds and slow collisional rethermalization. We report our work toward collision studies of $^{133}$Cs -$^6$Li and $^{133}$Cs-$^{133}$Cs in fields up to 1000G and its implications for optimal evaporation, as well as the implementation of quantum gate operations. [Preview Abstract] |
Friday, May 28, 2010 3:12PM - 3:24PM |
S5.00007: Towards strongly interacting Fermi-Fermi mixtures of ultracold atoms Cheng-Hsun Wu, Ibon Santiago, Jee-Woo Park, Peyman Ahmadi, Martin W. Zwierlein Strongly interacting mixtures of unequal fermionic species promise to allow access to novel states of matter, such as Cooper pairing without time-reversal symmetry, the FFLO (Fulde-Ferrell-Larkin- Ovchinnikov) state of Cooper pairs at finite momenta, and a basic form of quark (color) superfluidity. We will present our experiments on cooling a Fermi-Fermi mixture of the fermionic Alkalis $^6$Li and $^{40}$K. The difficulty of the low natural abundance of $^{40}$K (\%0.01) is typically overcome with the use of enriched, but expensive, $^{40}$K. In our approach we use two independent Zeeman slowers optimized for high atomic fluxes of non-enriched K and Li. This allows us to load 5 x $10^7$ fermionic K into a magneto-optical trap, and it also gives us access to the bosonic isotopes of $^{39}$K and $^{41}$K as possible sympathetic coolants for both $^6$Li and $^{40}$K. As a crucial step, we have produced a Bose-Einstein condensate of $^{41}$K by direct evaporation and we were able to sympathetically cool the fermion $^{40}$K. Our immediate goal is the production of a degenerate Fermi-Fermi mixture of $^6$Li and $^{40}$K. [Preview Abstract] |
Friday, May 28, 2010 3:24PM - 3:36PM |
S5.00008: Free Expansion of ultracold fermions in an optical lattice Ulrich Schneider, Lucia Hackermueller, Jens Philipp Ronzheimer, Sebastian Will, Simon Braun, Thorsten Best, Michael Schreiber, Kin Chung Fong, Immanuel Bloch Recent experiments with ultracold fermions in optical lattices face two main challenges in the quest of realizing complex strongly-correlated states: While the need to realize low entropy samples resulted in several recent proposals of advanced cooling schemes there remains the problem of the unknown adiabaticity timescales in these inhomogeneous systems. In order to measure the characteristic timescales of density redistribution, we experimentally investigate the free expansion of fermionic $^{40}$K atoms in an homogeneous optical lattice. In an initially non-interacting band-insulater, created in the combination of a blue-detuned optical lattice and a red-detuned optical dipole trap, interactions are introduced by use of a Feshbach resonance. Subsequently the expansion is initiated by quickly ramping down the dipole trap while retaining the optical lattice. In the case of negligible interactions, the atoms expand ballistically performing a continuous quantum walk. For interacting fermions, the expansion becomes diffusive with a density dependent diffusion constant that is independent of the sign of interactions. These measurements demonstrate previously unobserved transport dynamics and give insight into the characteristic timescales of density redistribution. [Preview Abstract] |
Friday, May 28, 2010 3:36PM - 3:48PM |
S5.00009: Phases of a 2D Bose Gas in an Optical Lattice Karina Jimenez-Garcia, Robert Compton, Yu-Ju Lin, William Phillips, James Porto, Ian Spielman We realize the Bose-Hubbard (BH) model with a $^{87}$Rb Bose- Einstein condensate (BEC) and measure condensate fraction to determine the Superfluid (SF) to Mott-Insulator (MI) transition as a function of atom density and lattice depth. We start with a 3D BEC in $|F=1, m_{F}=1\rangle$, in the presence of a magnetic field gradient along $\hat{z}$, and load it into a 3D optical lattice to get an ensemble of $\approx$60 2D systems along $\hat{z}$ and to realize the 2D BH model in $\hat{x}$- $\hat{y}$. With a MRI approach, we address a localized group of nearly identical 2D systems from the ensemble. We choose an rf magnetic field $B_{\textrm{rf}}$ to maximize the transfer from $|m_{F}=1\rangle$ to $|m_{F}=0\rangle$ using a 400 $\mu$s Blackman pulse. After the rf pulse the lattices are adiabatically ramped down. Simultaneously, all other confinement potentials are turned off and the atoms evolve in time of flight (TOF). During part of TOF a magnetic field gradient along $\hat{y}$ separates the $m_F$ components. Our results are in agreement with the Quantum Monte Carlo universal state diagram, suitable for trapped systems, introduced by Rigol ${\it et. al.}$(Phys. Rev. A 79, 053605 (2009)). [Preview Abstract] |
Friday, May 28, 2010 3:48PM - 4:00PM |
S5.00010: Interacting Bose-Fermi Mixtures in 3D Optical Lattice Potentials Sebastian Will, Thorsten Best, Simon Braun, Philipp Ronzheimer, Ulrich Schneider, Michael Schreiber, Kin Chung Fong, Lucia Hackerm\"uller, Tim Rom, Dirk-S\"oren L\"uhmann, Immanuel Bloch Mixtures of quantum gases in optical lattices form novel quantum many-body systems, whose properties are governed by the interplay of quantum statistics, inter- and intraspecies interactions, as well as the relative number of atoms of the components. In particular, degenerate Bose-Fermi mixtures have only recently come within experimental reach and stimulated theoretical investigations. A variety of quantum phases have been predicted including perturbed Mott insulating states, polaron-like quasi-particles or supersolid ordering. In our experiment we cool bosonic $^{87}$Rb and fermionic $^{40} $K down to simultaneous quantum degeneracy and investigate this Bose-Fermi mixture with tunable interspieces interactions in a three dimensional optical lattice. By studying the quantum phase evolution in an array of coherent states of $^{87}$Rb, we have been able to establish a tool to measure absolute interaction energies on lattice sites with high precision. In the presence of $^{40}$K, this technique reveals the marked influence of varying interspecies interactions on the atomic density distribution as well as the Bose-Bose and the Bose- Fermi interaction energies, quantitatively elucidating the role of interactions in the mixture. [Preview Abstract] |
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