Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session R02: Atoms in Optical Lattices II |
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Chair: Yang Wang, University of Maryland Room: Grand A |
Thursday, May 31, 2018 10:30AM - 10:42AM |
R02.00001: Towards the detection of a massive collective mode of the attractive Hubbard model: the $\eta$ mode Debayan Mitra, Elmer Guardado-Sanchez, Peter Brown, Peter Schauss, Waseem Bakr Goldstone’s theorem states that a system with spontaneously broken continuous symmetries possesses excitations that are massless bosons. A prototypical example is the phonon modes in a crystal which result from the breaking of translational symmetry. At half-filling, the attractive Hubbard model is known to possess not only one SU(2) symmetry, that of the spin, but also another SU(2) symmetry attributed to the "pseudospin". The pseudospin symmetry results in a degeneracy between superfluid and charge-density-wave ordered ground states and there are no massive modes in the excitation spectrum. The symmetry can be explicitly broken by doping the system away from half-filling, leading to the prediction of a massive mode known as the $\eta$ mode, corresponding to rotations between these orders. In this talk, I will present the theoretical background for understanding this mode and discuss our progress towards its experimental detection, including the generation of traveling wave potentials in a Hubbard system with a spatial light modulator and the phase sensitive detection of charge density oscillations in the system. [Preview Abstract] |
Thursday, May 31, 2018 10:42AM - 10:54AM |
R02.00002: Persistent nearest-neighbor coherence of a Mott insulator in a trimerized Kagome lattice Thomas Barter, Tsz-Him Leung, Masayuki Okano, Maxwell Block, Norman Yao, Dan Stamper-Kurn Mott insulating states are characterized by the absence of long range phase coherence, whilst short range coherence is typically extinguished as the tunneling is suppressed. We report a persistent nearest-neighbor phase coherence in a two dimensional Mott insulator of ultracold $^{87}$Rb atoms. We realize an optical trimerized Kagome lattice, with strong intra-trimer tunneling and weak inter-trimer tunneling and create a novel Mott insulating state of strongly coupled local orbitals. Evidence for this state comes from interpreting the momentum-space distribution obtained from time of flight. As the inter-trimer tunneling is suppressed, we see a persistent nearest-neighbor coherence. Furthermore we show an asymmetry between the intra-trimer, and inter-trimer coherences by imprinting a phase pattern on the lattice. Finally, we discuss the possibility of engineering insulating states with fractional number and angular momentum. [Preview Abstract] |
Thursday, May 31, 2018 10:54AM - 11:06AM |
R02.00003: Josephson effect and $SU (N)$ superfluidity in an optical lattice clock Leonid Isaev, Ana Maria Rey Josephson effect is a quantum interference phenomenon that results from weak coupling (junction) of two superfluid systems. It offers an invaluable tool to perform phase-sensitive measurements of condensate wavefunctions. In this work, we propose a protocol to realize a Josephson junction with $SU (N)$-symmetric [$N$ is the number of populated nuclear-spin states] fermionic ${}^{87}$Sr atoms in a quasi-1D optical lattice that consists of weakly-coupled 2D harmonically-trapped clouds (pancakes). Within each pancake, the axial confinement couples a two-atom scattering channel and their molecular channel, leading to an $s$-wave superfluid state. These superfluid correlations can be enhanced by using a photo-association laser that drives the formation of bound pairs and effectively reduces the molecular-channel detuning. A weak inter-pancake single-atom tunneling gives rise to a Josephson current along the system, which can be detected thanks to the ultra-high spectral resolution and exquisite controllability of the Sr optical lattice clock transition. We also describe ways of exploiting this Josephson effect to probe the $SU (N)$ structure of the emergent superfluid state. [Preview Abstract] |
Thursday, May 31, 2018 11:06AM - 11:18AM |
R02.00004: Microscopic studies of cold-atom Fermi-Hubbard antiferromagnets Christie Chiu, Geoffrey Ji, Muqing Xu, Anton Mazurenko, Daniel Greif, Markus Greiner Quantum gas microscopy of ultracold fermionic atoms in optical lattices allows studying strongly correlated low-temperature phases in the Hubbard model. Through an entropy redistribution technique we have demonstrated long-range antiferromagnetic order extending over our entire sample, a disk spanning ten sites across filled with a two-component spin mixture of ultracold fermionic Li-6 atoms in a square lattice. Our microscope provides access to quantities such as the site-resolved spin correlation function, spin structure factor, and full counting statistics of the staggered magnetization. By hole doping the system away from half-filling we explore regimes of the Hubbard model phase diagram where precise numerical studies become challenging. We study the interplay between hole motion and the antiferromagnetic order: when a hole tunnels in an antiferromagnet, it distorts the surrounding order and may form a spinon-holon string of distorted spin order. This could be an essential aspect of high-temperature superconductivity in cuprates, and the readout of our microscope allows us to directly address this question. We discuss our progress in the search for signatures of these string configurations and study the dynamics of mobile holes in an antiferromagnet. [Preview Abstract] |
Thursday, May 31, 2018 11:18AM - 11:30AM |
R02.00005: Non-Hermitian Kondo effect in ultracold alkaline-earth atoms Masaya Nakagawa, Norio Kawakami, Masahito Ueda The Kondo effect is one of the most important phenomena in strongly correlated many-body systems. It consists of a localized impurity spin and a surrounding fermion cloud which antiferromagnetically couples with the impurity, thereby realizing an emergent many-body bound state called the Kondo singlet. Motivated by the recent progress in cold-atom experiments [1], which have realized the Kondo Hamiltonian using ultracold Yb atoms, we extend the paradigm of the Kondo effect towards open quantum systems [2]. We consider the Kondo Hamiltonian by taking into account the effect of inelastic scattering with the impurity spin, which gives rise to a non-Hermitian term in the exchange interaction. Using the renormalization group (RG) calculation, we find that the Kondo effect shows an anomalous RG flow in the non-Hermitian case, accompanied by a new energy scale unique to the dissipative system. We confirm our prediction of the RG flow using an exact solution based on a generalized Bethe ansatz. [1] L. Riegger et al., arXiv:1708.03810. [2] M. Nakagawa, N. Kawakami, and M. Ueda, in preparation. [Preview Abstract] |
Thursday, May 31, 2018 11:30AM - 11:42AM |
R02.00006: Enhancement and sign change of magnetic correlations in a driven quantum many-body system Kilian Sandholzer, Frederik G\"org, Michael Messer, Joaquin Minguzzi, Gregor Jotzu, Remi Desbuquois, Tilman Esslinger Periodic driving can be used to coherently control the properties of a many-body state and to realize new phases which are not accessible in static systems. In this context, cold fermions in optical lattices provide a highly tunable platform to investigate driven many-body systems and additionally offer the prospect of quantitative comparisons to theoretical predictions. We implement a driven Fermi-Hubbard model by periodically modulating a 3D hexagonal lattice. Driving the system near-resonantly to the interaction enables us to independently control the single particle tunneling and the magnetic exchange energy. As a consequence, we are able to show that anti-ferromagnetic correlations in a fermionic many-body system can be enhanced or even switched to ferromagnetic correlations. Furthermore, a detailed study of the dynamics of double occupancies in the driven many-body system gives insights into thermalization, adiabatic preparation and heating. [Preview Abstract] |
Thursday, May 31, 2018 11:42AM - 11:54AM |
R02.00007: Lattice-induced rapid formation of spin singlets in spin-1 spinor condensates Tao Tang, Lichao Zhao, Zihe Chen, Yingmei Liu We experimentally demonstrate that combining a spinor Bose-Einstein condensate with cubic optical lattices significantly relaxes three strict constraints and enables a rapid generation of spin singlets using ultracold spin-1 atoms. Our observations confirm that spin singlets of spin-1 atoms are brought into experimentally accessible regions by two key lattice-modified parameters, which are the lattice-enhanced interatomic interactions and substantially reduced atom number in individual lattice sites. About 80 percent of atoms in the lattice-confined spin-1 spinor condensate are found to form spin singlets, after the atoms cross first-order superfluid to Mott-insulator phase transitions in an ideal lattice ramp sequence. In addition, we develop a phenomenological model that well describes our observations without adjustable parameters. [Preview Abstract] |
Thursday, May 31, 2018 11:54AM - 12:06PM |
R02.00008: Formation of a spin texture in a quantum gas coupled to a cavity Lorenz Hruby, Manuele Landini, Nishant Dogra, Katrin Kroeger, Tobias Donner, Tilman Esslinger We experimentally study the self-organization of single and multi-component 87Rb Bose-Einstein condensates, strongly coupled to a single-mode optical cavity and subject to an off-resonant pump field, propagating transversely to the cavity axis. We identify the roles of the scalar and the vectorial components of the atomic polarizability tensor for the atom-light coupling using a driving field of adjustable linear polarization. When prepared in only one of the Zeeman-split magnetic sublevels of the F=1 manifold, the atomic cloud undergoes a Dicke-type phase transition into a density-modulated state. We study as a function of the different polarization angles of the pump laser with respect to the cavity axis the dependency of the phase transition threshold and the relative phase between the pump and cavity field for the three magnetic sublevels. In both cases we find good agreement with our theoretical analysis. Preparing the condensate in a balanced mixture of the mF=+1 and mF =-1 sublevels, we observe a magnetically ordered state below a critical angle of the pump polarization. The observed spin textures originate in a cavity mediated spin-dependent interaction between the atoms. [Preview Abstract] |
Thursday, May 31, 2018 12:06PM - 12:18PM |
R02.00009: Autonomous Stabilization of Photonic Many-Body Systems Brendan Saxberg Synthetic photonic systems are a promising platform for studying strongly interacting and highly correlated quantum materials. These systems pose a challenge for preparing finite photon-number states. Here we present on an autonomous stabilization scheme for incompressible photonic many-body states at non-zero chemical potential. The scheme is analogous to optical pumping - a single lattice site (qubit) is continuously driven to the second excited state and quickly loses a photon through coupling to a lossy resonator, stabilizing the qubit in the first excited state. Coupling this site to a larger target system fills the many-body system up to a target state if the system is incompressible w.r.t. particle number. We present numerical and experimental results on stabilizing a Mott Insulator phase in an eight-site Bose-Hubbard lattice implemented in the Circuit QED framework. We then investigate stabilization performance with two or more lattice sites being stabilized, and stabilization of different many-body systems. This work provides a potential route to topologically protected states, for example in a topological microwave cavity lattice with qubit mediated interactions. [Preview Abstract] |
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