Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session C07: Topological Phenomena in Ultracold Gases |
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Chair: Han Pu, Rice University Room: Wisconsin Center 103AB |
Tuesday, May 28, 2019 10:30AM - 10:42AM |
C07.00001: Observation of band gap closing in a synthetic Hall tube of neutral fermions. Jeong Ho Han, Jin Hyoun Kang, Yong-il Shin The Harper-Hofstadter Hamiltonian is the essential model for studying the quantum Hall physics of lattice systems. Recently, many types of Hall systems have been realized in the optical lattice experiments. In this talk, we present our experimental realization of a synthetic Hall lattice system with three-leg tube geometry for ultracold fermionic ytterbium atoms in a 1D optical lattice. The legs of the synthetic tube are composed of three atomic hyperfine spin states, and the cyclic inter-leg links are generated by two-photon Raman transitions between the spin states, resulting in a uniform gauge flux $\phi $ penetrating each side plaquette of the tube. Using quench dynamics, we investigate the band structure of the Hall system for a commensurate flux $\phi =$2$\pi $/3. The momentum-resolved analysis of the quench dynamics reveals the band gap closing behavior at the critical point of a topological phase transition for the Hall tube system as its boundary condition evolves from periodic to open by varying the one of the inter-leg coupling strengths. We also investigate the emergent topological features of the Hall tube system for the case of incommensurate gauge flux. [Preview Abstract] |
Tuesday, May 28, 2019 10:42AM - 10:54AM |
C07.00002: Quantum Hall Effect with Composites of Magnetic Flux Tubes and Charged Particles Marija Todoric, Dario Jukic, Danko Radic, Hrvoje Buljan, Marin Soljacic Composites formed from charged particles and magnetic flux tubes, proposed by Wilczek, are one model for anyons, particles obeying fractional statistics[1]. Anyons exist in a two-dimensional (2+1 D) space[1]. Apart from the fundamental interest in anyons, non-Abelian anyonic quasiparticles could become the building blocks of fault-tolerant topological quantum computers. Here [2] we propose a scheme for realizing charged flux tubes, in which a charged object with an intrinsic magnetic dipole moment is placed between two semi-infinite blocks of a high permeability ($\mu_r$) material, and the images of the magnetic moment create an effective flux tube. We show that the scheme can lead to a realization of Wilczek's anyons, when a 2D electron system exhibiting the integer quantum Hall effect (IQHE) is sandwiched between two blocks of the high-$\mu_r$ material with a temporally fast response (in the cyclotron and Larmor frequency range). The signature of Wilczek's anyons is a slight shift of the resistivity at the plateau of the IQHE. [1] F. Wilczek, Phys. Rev. Lett. 49, 957 (1982). [2] M. Todori\'c, D. Juki\'c, D. Radi\'c, M. Solja\v{c}i\'c, and H. Buljan, Phys. Rev. Lett. 120, 267201 (2018). [Preview Abstract] |
Tuesday, May 28, 2019 10:54AM - 11:06AM |
C07.00003: Topological invariant for interacting systems at finite temperature Maximilian Kiefer-Emmanouilidis, Razmik Unanyan, Michael Fleischhauer As shown in [1], the Ensemble Geometric Phase (EGP) based on the many-body polarization is a meaningful topological invariant for finite-temperature states of non-interacting fermions. Here we show that the same applies to interacting systems with topological order in the ground state. The EGP approaches the T$=$0 many-body Zak phase when going to the thermodynamic limit of infinite system size and its winding is thus a topological invariant. This opens a new approach for the measurement of topological invariants under realistic experimental conditions as well as for identifying topological order in numerical simulations. We verify our predictions with numerical simulations of the extended super-lattice Bose-Hubbard model at quarter filling, which has symmetry-protected topology with fractional charges. \textit{[1] C.E. Bardyn, L. Wawer, A. Altland, M. Fleischhauer, S. Diehl, PRX. 8, 011035 (2018)} [Preview Abstract] |
Tuesday, May 28, 2019 11:06AM - 11:18AM |
C07.00004: Anyons from Three-Body Hard-Core Interactions in One Dimension Nathan Harshman, Adam Knapp Traditional anyons in two dimensions have generalized exchange statistics governed by the braid group. By analyzing the topology of configuration space, we discover that an alternate generalization of the symmetric group governs particle exchanges when there are hard-core three-body interactions in one-dimension. We call this new exchange symmetry the traid group and demonstrate that it has abelian and non-abelian representations that are neither bosonic nor fermionic, and which also transform differently under particle exchanges than braid group anyons. We show that generalized exchange statistics occur because, like hard-core two-body interactions in two dimensions, hard-core three-body interactions in one dimension create defects with co-dimension two that make configuration space no longer simply-connected. Ultracold atoms in effectively one-dimensional optical traps provide a possible implementation for this alternate manifestation of anyonic physics. [Preview Abstract] |
Tuesday, May 28, 2019 11:18AM - 11:30AM |
C07.00005: Synthetic anyons in noninteracting systems Frane Lunic, Marija Todoric, Tena Dubcek, Dario Jukic, Hrvoje Buljan We demonstrate that anyons, particles with exotic exchange statistics, can in principle be synthesised by perturbing 2D noninteracting many-body systems with specially tailored localized probes. This approach stands in contrast to the fractional quasiparticle excitations of strongly correlated interacting systems observed in experiments thus far. We consider the case of noninteracting 2D electron gas in a uniform magnetic field (IQHE) perturbed with external solenoids carrying a magnetic flux that is a fraction of the flux quantum. This results in charge-flux composites that can be considered Wilczek's anyons. The flux-dependent fractional statistics of the wave function in the coordinates of the solenoids is demonstrated analytically and numerically by determining the statistical contribution to the Berry phase accumulated as a solenoid traverses a closed path around another solenoid. This result holds if a small amount of disorder is introduced into the system. We discuss possible platforms and probes for experimental realization of this idea, including noninteracting fermions in a 2D periodic potential, ultra-cold atoms, and magnetic needles suspended above a 2D electron gas heterostructure grown on a material of high magnetic permeability. [Preview Abstract] |
Tuesday, May 28, 2019 11:30AM - 11:42AM |
C07.00006: Measurement of Tan's contact in SU($N$) fermions Zejian Ren, Bo Song, Chengdong He, Elnur Hajiyev, Entong Zhao, Qianhang Cai, Jeongwon Lee, Gyu-Boong Jo Contact interactions play a fundamental role for understanding correlated quantum systems from microscopic models. For example, the 1/$k^4$ momentum tail, the weight of which is known as Tan's contact, reveals a set of universal relations in interacting atomic systems. Nevertheless, the experimental measurement of contact has still remained unexplored for multi-component fermions with high spins. Here, we report on the measurement of $s$-wave contact parameter in a cold spin-balanced gas of $^{173}$Yb atoms with SU($N$) symmetry. The high-momentum tail is recorded after time-of-flight expansion, and Tan's contact is directly quantified with a tunable number of spin component $N$ without changing the number of atoms per component. We experimentally verify the linear increase in the contact with $N$ providing experimental confirmation of the SU($N$) interaction. Furthermore, we investigate the momentum distribution of SU($N$) fermions at the low momentum regime showing that multi-component fermions with large $N$ exhibit a more bosonic behavior. Our measurement directly reveals the interaction effect in a multi-component Fermi gas with SU($N$) symmetry, and paves the way for study of many-body physics with high spins. [Preview Abstract] |
Tuesday, May 28, 2019 11:42AM - 11:54AM |
C07.00007: Dynamical Fermionization, Tan Contact, and Scalings for a Strongly Interacting Gas after quench. Shah Saad Alam, Tim Skaras, Li Yang, Han Pu Dynamical fermionization has been theoretically demonstrated for hard core spinless bosonic and anyonic gases in 1D. It refers to the phenomenon where, after the initial harmonic confinement is turned off, the momentum distribution of the system asymptotically approaches that of a free Fermi gas. Evidence of dynamical fermionization was experimentally shown for 1D hard core bosonic gases recently. We extend this study to a system of 1D spinor gas in the strongly interacting regime, and analytically prove that the asymptotic momentum distribution of a spin component after the harmonic trap is turned off resembles the initial real space density profile of that component in the trap. As illustrative examples, we present two particle and few particle calculations for specific spinor systems. Finally, we present the Tan contact for a strongly interacting spinor system, as well as its scaling during expansion. [Preview Abstract] |
Tuesday, May 28, 2019 11:54AM - 12:06PM |
C07.00008: Topological Phases of Fermions in Kagome Optical Lattices Vito Scarola, Mengsu Chen, Hoi Hui Frustration can favor topological states of matter over conventionally ordered states. We use numerical diagonalization and mean field theory to study models of fermionic atoms and molecules placed in kagome optical lattices. We show that just the long range part of dipolar interactions between fermions can drive the creation of a topological Mott insulator. We also study applications of applied synthetic fields using optical flux lattices and laser assisted tunneling. We find that effective magnetic fields lead to topological phases, including the chiral spin liquid, even for atoms interacting with only the contact interaction. Experimental challenges for realizing these topological states with atoms in optical lattices are discussed. [Preview Abstract] |
Tuesday, May 28, 2019 12:06PM - 12:18PM |
C07.00009: Floquet approach to $\mathbb{Z}_{2}$ lattice gauge theories with ultracold atoms in optical lattices Christian Schweizer, Fabian Grusdt, Moritz Berngruber, Luca Barbiero, Eugene Demler, Nathan Goldman, Immanuel Bloch, Monika Aidelsburger $\mathbb{Z}_2$ lattice gauge theories (LGTs) are of high interest in condensed matter physics and topological quantum computation. The investigation of strongly-interacting regimes, however, is especially challenging and in general difficult to access with conventional numerical methods. Here, we take a first step using analog quantum simulations and present an approach to realize $\mathbb{Z}_2$ LGTs. We use a two-component mixture of ultracold bosonic atoms with strong on-site interactions in an optical two-site potential together with resonant periodic driving. For particular driving parameters, the effective Floquet Hamiltonian exhibits $\mathbb{Z}_2$ symmetry. We study the dynamics of the system for different initial states and find that it is well described by a full time-dependent description. Moreover, it is non-trivial due to the imposed gauge constraints and in agreement with predictions from the ideal $\mathbb{Z}_2$ LGT. We reveal challenges that arise due to symmetry-breaking terms, which may be relevant for any experimental implementation, and outline potential pathways to overcome them. The results provide important insights for studies of LGTs based on Floquet techniques and the two-site model constitutes a minimal instance for extended LGTs coupled to matter. [Preview Abstract] |
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