Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session J2: Exotic Phases |
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Chair: Jonathan Simon, University of Chicago Room: 200B |
Wednesday, June 5, 2013 2:00PM - 2:12PM |
J2.00001: Strongly interacting quantum phases of polarized dipolar bosons in multi-layered optical lattice Barbara Capogrosso-Sansone, Arghavan Safavi-Naini, Anatoly Kuklov We present a Quantum Monte Carlo study of dipolar bosons confined in $N$ tubes parallel to each other with the dipole moments polarized perpendicular to the tubes. Each tube represents 1d optical lattice, and no inter-tube tunneling as well as no double-occupation in each tube are allowed. Using a new multi-worm algorithm, the following phases have been found: i) Superfluid of chains, where each chain represents a bound state of $N$ bosons, one from each tube; ii) Checker board solid of chains at 1/2 filling; iii) Independent superfluids in each tube. [Preview Abstract] |
Wednesday, June 5, 2013 2:12PM - 2:24PM |
J2.00002: ABSTRACT WITHDRAWN |
Wednesday, June 5, 2013 2:24PM - 2:36PM |
J2.00003: Bose and Fermi Gases of Ultracold Ytterbium in a Triangular Optical Lattice Alexander Thobe, Soeren Doerscher, Bastian Hundt, Andre Kochanke, Christoph Becker, Klaus Sengstock Quantum gases of alkaline-earth like atoms such as Calcium, Strontium and Ytterbium (Yb) open up exciting new possibilities for the study of many body physics in optical lattices, ranging from SU(N) symmetric spin Hamiltonians to the Kondo Lattice Model. Here, we present experimental studies of ultracold bosonic and fermionic Yb quantum gases. Unlike other experiments studying ultracold alkaline earth-like atoms, we have implemented a 2D-MOT instead of a Zeeman slower as a source of cold atoms. From the 2D-MOT, operating on the broad ${^{1}S_{0}}\rightarrow{^{1}P_{1}}$ transtition, the atoms are directly loaded into the 3D-MOT operating on a narrow intercombination line. The atoms are then evaporatively cooled to quantum degeneracy in a crossed optical dipole trap. With this setup we routinely produce BECs and degenerate Fermi gases of different Yb isotopes. Moreover, we present first results on spectroscopy of an interacting fermi gas on the ultranarrow ${^{1}S_{0}}\rightarrow{^{3}P_{0}}$ clock transition in a magic wavelength optical lattice. In future experiments, this spectroscopy will serve as a versatile tool for interaction sensing and selective addressing of atoms in a wavelength tunable, state dependent, triangular optical lattice, which we are currently implementing. [Preview Abstract] |
Wednesday, June 5, 2013 2:36PM - 2:48PM |
J2.00004: Interferometric measurement method for $Z_2$ invariants of time-reversal invariant topological insulators Fabian Grusdt, Dmitry Abanin, Eugene Demler Recently experiments with ultracold atoms started to explore topological phases in 1D optical lattices. While transport measurements are challenging in these systems, ways to directly measure topological quantum numbers using a combination of Bloch oscillations and Ramsey interferometry have been explored (Atala et.al., arXiv:1212.0572). In this talk I will present ways to measure the $Z_2$ topological quantum numbers of two and three dimensional time-reversal invariant (TR) topological insulators. In this case non-Abelian Bloch oscillations can be combined with Ramsey interferometry to map out the topological properties of a given band-structure. Our method is very general and works even in the presence of accidental degeneracies. The applicability of the scheme is discussed for different theoretically proposed implementations of TR topological insulators using ultracold atoms. [Preview Abstract] |
Wednesday, June 5, 2013 2:48PM - 3:00PM |
J2.00005: Direct Measurement of the Zak phase in Topological Bloch Bands Marcos Atala, Monika Aidelsburger, Julio T. Barreiro, Dmitry Abanin, Takuya Kitagawa, Eugene Demler, Immanuel Bloch In this talk I will present our latest results on the direct measurement of the Zak phase for a dimerized optical lattice, which models polyacetylene. The experimental protocol consists of a combination of Bloch oscillations and Ramsey interferometry from where we extract the Zak phase - the Berry phase acquired during an adiabatic motion of a particle across the Brillouin zone - which can be viewed as an invariant characterizing the topological properties of the band. This work establishes a new general approach for probing the topological structure of Bloch bands in optical lattices. [Preview Abstract] |
Wednesday, June 5, 2013 3:00PM - 3:12PM |
J2.00006: Photonic topological insulators Mikael Rechtsman, Julia Zeuner, Yonatan Plotnik, Yaakov Lumer, Stefan Nolte, Mordechai Segev, Alexander Szameit We present the first experimental observation of Photonic Topological Insulators (Photonic TIs). TIs are a new state of matter, which are bulk insulators, but conduct electrons on the surface. In photonic TIs, the propagating waves are electromagnetic, rather than electronic (in our case, visible light). Beyond their fundamental signifiucance, photonic TIs have also been suggested for a number of applications, including highly robust optical delay lines, on-chip optical diodes, and spin-cloaked photon sources. In solid-state TIs, topological protection is achieved by virtue of the Kramers degeneracy, which does not apply to photons. Therefore, for a non-fermionic TI, another mechanism is required. Our system is composed of an array of helical waveguides arranged in a honeycomb lattice. The helicity induces a fictitious, time-varying electric field, and the structure becomes equivalent to a Floquet TI (proposed by Lindner et. al.). By probing the diffraction of light through the lattice, we demonstrate topologically-protected edge states, scatter-free propagation around corners and upon encountering defects. Our setting will allow for the probing of mean-field interactions in TIs through optical nonlinearities, as well as the effects of controllable disorder. [Preview Abstract] |
Wednesday, June 5, 2013 3:12PM - 3:24PM |
J2.00007: Observation of photonic edge states in Silicon Mohammad Hafezi, Jingyun Fan, Sunil Mittal, Alan Migdall, Jacob Taylor Systems with topological order exhibit exotic phenomena including fractional statistics. While most systems with topological order have been electronic, advances in our understanding of synthetic gauge fields have enabled realization of topological order in cold atoms or even with photons. We demonstrate the experimental realization of synthetic magnetic fields for infrared photons at room temperature. Our implementation corresponds to a synthetic spin-orbit Hamiltonian, which requires linear optics and does not break time reversal symmetry. As a direct proof of topological order, we observe for the first time, edge states for light in a two-dimensional system. This realization in principle allows investigation of wider range of topological order in photonics system by entering the non-interacting and many-body regimes. [Preview Abstract] |
Wednesday, June 5, 2013 3:24PM - 3:36PM |
J2.00008: Electromagnetically Induced Flux Lattices for 2D Photon Gases Johannes Otterbach, Jonathan Simon The intense interest in topological states of matter has triggered an outpouring of effort to develop artificial gauge fields for ultracold atomic gases, where access to extraordinary control provides a promising route to the creation of synthetic materials on-demand. However, engineering \textit{scalable} magnetic fields for neutral particles has proven difficult, resulting in either low flux densities or small system sizes. A new, scalable approach to creation of high flux densities for neutral atoms employs a so-called ``optical flux lattice,'' which is a spinor lattice of berry-phase vortices [1]. Here we discuss an extension of this idea to photonic systems: using a coherently driven atomic ensemble, we modify the optical response of a near-degenerate cavity to mimick an effective optical flux lattice for photonic polarization states. This enables us to engineer photonic Bloch-bands with non-zero Chern number, giving rise to chiral edge-modes in the presence of an additional potential. The single particle bulk- and edge-dispersion relations may be directly probed in cavity transmission. Combined with interactions, the proposed hybrid system presents an ideal tool to study strongly correlated photon states. \\[4pt] [1] N. R. Cooper, Phys. Rev. Lett. 106, 175301 (2011). [Preview Abstract] |
Wednesday, June 5, 2013 3:36PM - 3:48PM |
J2.00009: Coherent spin and spin-spatial excitations in an ultracold Fermi gas Christoph Becker, Jannes Heinze, Jasper Krauser, Nick Flaeschner, Klaus Sengstock, Andre Eckardt, Ulrich Ebling, Maciej Lewenstein Ultracold fermions with large spin provide ideal model systems for the investigation of high-spin magnetic properties beyond conventional electronic magnetism. Here, we report on detailed studies of collective spin and spin-spatial excitations in a binary high-spin Fermi mixture. For the first time we observe collective coherent spin-changing dynamics in a fermionic bulk system and find strong indications that Pauli blocking drastically extends the coherence time for low enough temperatures. Introducing a coupling to spatial excitations in such a high-spin system leads to the emergence of multi-component spin waves characterized by tensorial order in the spin- and spatial degrees of freedom. In particular we measure counterflow spin currents in the individual spin components, which we engineer and fully control by tuning the initial state. For all our results we find excellent agreement with mean-field calculations. Our findings open new perspectives for further studies of high-spin magnetic properties such as S\textgreater 1/2 Mott insulators or color superfluidity. [Preview Abstract] |
Wednesday, June 5, 2013 3:48PM - 4:00PM |
J2.00010: Negative absolute temperature for mobile particles Simon Braun, Philipp Ronzheimer, Michael Schreiber, Sean Hodgman, Immanuel Bloch, Ulrich Schneider Absolute temperature is usually bound to be strictly positive. However, negative absolute temperature states, where the occupation probability of states increases with their energy, are possible in systems with an upper energy bound. So far, such states have only been demonstrated in localized spin systems with finite, discrete spectra. We realized a negative absolute temperature state for motional degrees of freedom with ultracold bosonic $^{39}$K atoms in an optical lattice, by implementing the attractive Bose-Hubbard Hamiltonian. This new state strikingly revealed itself by a quasimomentum distribution that is peaked at maximum kinetic energy. The measured kinetic energy distribution and the extracted negative temperature indicate that the ensemble is close to degeneracy, with coherence over several lattice sites. The state is as stable as a corresponding positive temperature state: The negative temperature stabilizes the system against mean-field collapse driven by negative pressure. Negative temperatures open up new parameter regimes for cold atoms, enabling fundamentally new many-body states. Additionally, they give rise to several counterintuitive effects such as heat engines with above unity efficiency.\\[4pt] [1] S. Braun \textit{et al}, \textit{Science} 339, 52 (2013). [Preview Abstract] |
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