Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L13: Topological States in AMO Systems II |
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Sponsoring Units: DAMOP Chair: Ferdinand Brenneke, Universität Bonn, Germany Room: 272 |
Wednesday, March 15, 2017 11:15AM - 11:27AM |
L13.00001: Topological protection of photonic mid-gap cavity modes Wladimir A. Benalcazar, Jiho Noh, Sheng Huang, Matthew J. Collins, Kevin Chen, Taylor L. Hughes, Mikael Rechtsman Defect modes in two-dimensional periodic photonic structures have found use in a highly diverse set of optical devices. Here, we show in theory and experiment that a photonic topological crystalline insulator structure can be used to generate topological defect-localized modes. These defect modes are protected by chiral and crystalline symmetries, and have resonance frequencies in the middle of the photonic band gap (which minimize the mode volume). This protection of zero-dimensional states (defect modes) embedded in a two-dimensional environment constitutes a novel form of topological protection that has not been previously demonstrated. [Preview Abstract] |
Wednesday, March 15, 2017 11:27AM - 11:39AM |
L13.00002: Two-dimensionally confined topological edge states in photonic crystals Sabyasachi Barik, Hirokazu Miyake, Wade DeGottardi, Edo Waks, Mohammad Hafezi Topologically-protected edge states were initially studied in condensed matter systems, but more recently they have also been experimentally realized in photonic systems operating at optical frequencies. A major goal in the field of topological photonics is to couple such topological photonic edge states with quantum emitters, which is expected to give rise to exotic phenomena such as many-body position-independent scattering, dimerization of driven emitters, and fractional quantum Hall states, and could be a platform for robust quantum information processing. Towards this goal, we will present our results from numerical simulations of a new photonic crystal design we proposed which gives rise to topological edge states in a dielectric material which is compatible with epitaxially-grown quantum emitters in a planar geometry. The simulations show that the system possesses helical edge states that is robust to certain types of disorders. We will also report on our experimental progress, where we have observed the robustness of transmission spectra of topological waveguides made of InP membranes embedded with InAs quantum dots. [Preview Abstract] |
Wednesday, March 15, 2017 11:39AM - 11:51AM |
L13.00003: Topological frequency conversion Ivar Martin, Gil Refael, Bertrand Halperin We study the problem of arbitrarily strong multi-tonal drive applied to non-linear systems. The dynamics has a natural representation in terms of ``transport" in a multi-dimensional Floquet space, with an applied ``electric" field (whose components are proportional to the drive frequencies). The number of the Floquet space dimensions equals the number of {\em irrationally} related drive frequencies. In particular, for two-tone drive, when the band structure in the 2D Floquet space is topologically non-trivial (has non-zero Chern number, $C$), we find that there is a topological pumping of energy between the frequencies $\omega_1$ and $\omega_2$, with the rate $P_{12} = -P_{21}= (C/2\pi)\hbar \omega_1\omega_2$. This pumping is the analog of the transverse response in a conventional topological insulator. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L13.00004: Symmetry-protected zero-mode laser with a tunable spatial profile Li Ge Majorana zero modes in condense matter systems have attracted considerable interest in topological quantum computation. In contrast, while robust zero modes have been observed in various photonic lattices, it remains an open question whether they can be used for the same purpose. To advance significantly the state-of-the-art in zero-mode photonics, new inspirations are needed for a better design and control of photonic systems. Using the zero modes protected by non-Hermitian particle-hole symmetry in a photonic lattice and the spatial degrees of freedom they offer, we propose a single-mode, fixed-frequency, and spatially tunable zero-mode laser. The system does not need to have zero modes before a localized pump is applied; they are created by the spontaneous restoration of particle-hole symmetry. By modifying this process using different pump configurations, we present a versatile way to tune the spatial profile of our zero-mode laser, with its lasing frequency pinned at the zero energy. Such a zero-mode laser may find applications in telecommunication, where spatial encoding is held by some to be last frontier of signal processing. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L13.00005: Quantum Interference Of Topological Edge-States Jean-Luc Tambasco, Giacomo Corrielli, Robert Chapman, Andrea Crespi, Inna Krasnokutska, Oded Zilberberg, Roberto Osellame, Alberto Peruzzo Quantum photonics is a vibrant field that promises to enhance information processing by harnessing quantum effects in single photons. Many platforms used to manipulate quantum states suffer high loss and noise, limiting their scalability. Topology introduces the idea of robust states known as edge-states and recently, topological states have been demonstrated in photonic systems, and used to effectively transport light. We report quantum interference of edge-states in a photonic chip. High control over the circuit layout is achieved using femtosecond laser-written waveguides in glass. These results demonstrate on chip quantum state transfer and quantum interference of photonic topological states, providing a route to robust quantum information processing. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L13.00006: Symmetry-enforced quantum spin Hall insulators in $\pi$-flux models Jiaxin Wu, Tin-Lun Ho, Yuan-Ming Lu We prove a Lieb-Schultz-Mattis theorem for the quantum spin Hall effect (QSHE) in $\pi$-flux models. In the presence of time reversal, U(1) charge conservation and magnetic translation ($\pi$-flux per unit cell) symmetries, if a gapped Hamiltonian has a unique symmetric ground state at half filling (one electron per unit cell), it can only be a QSH insulator i.e. a trivial Mott insulator ground state is forbidden. We further show that such a symmetry-enforced QSHE can be realized in cold atoms, by shaking optical lattices and applying an oscillating Zeeman field. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L13.00007: Long-range entanglement and $\mathbb{Z}_2$ topological order of hardcore lattice bosons in the strong-interaction limit Wei Wang, Barbara Capogrosso-Sansone We investigate long-range entanglement properties of a generic class of hardcore lattice boson models governed by two-body interactions. We propose a scenario to explain how $\mathbb{Z}_2$ topological order rises in the strong-interacting limit. We use a local unitary transformation which maps ground states of the original Hamiltonian to ground states of an exactly solvable model. The existence of $\mathbb{Z}_2$ topological order in the exactly solvable model is closely related to topological properties of a surface code. We study the topological ground state degeneracy and locally indistinguishability of ground states in the solvable model and demonstrate a relationship between the Z2 topological order of the original two-body interacting model and that of a four- or higher-than-four-body interacting model. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L13.00008: Transition to a fractional Chern insulator state in a realistic cold atom model Johannes Motruk, Frank Pollmann The engineering of topological band structures in optical lattices for ultracold atoms hosts the possibility of creating exotic states of matter. A promising experimental setup has been presented by Aidelsburger et al. [Nat. Phys. 11, 162 (2015)] where the behavior of bosonic atoms in an optical lattice is governed by the Harper-Hofstadter Hamiltonian and the Chern number of the lowest band has experimentally been determined to be unity. This model harbors the possibility of hosting a fractional Chern insulator (FCI) state for a partially filled band and interacting particles. However, in order to tune the system into this phase, it is of crucial importance to know the characteristics of the transition from a non-topological phase into the FCI when crossing over from a trivial to a topological band structure. Using the density matrix renormalization group, we investigate this transition at filling factor $\nu = 1/2$ of the lowest band and show that the FCI state is stable over an extended parameter region. [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L13.00009: Attractive fermions in a 2D optical lattice with spin-orbit coupling: Charge order, superfluidity, and topological signatures Peter Rosenberg, Hao Shi, Shiwei Zhang Exotic states of matter, including high-$T_c$ superconductors, and topological phases, have long been a focus of condensed matter physics. With the recent advent of artificial spin-orbit coupling in ultracold gases, and the remarkable experimental control and enhanced interactions provided by optical lattices, a broad range of novel strongly correlated systems are quickly becoming experimentally accessible. One system of particular interest, given its potential impact on spintronics and quantum computation, is a 2D optical lattice of fermionic atoms with attractive interaction. Here we examine the combined effects of Rashba spin-orbit coupling and interaction in this system, with a focus on the pairing, charge, and spin properties of the ground state, which are computed using the numerically exact auxiliary-field quantum Monte Carlo technique. In addition to illuminating the behavior of this exotic charge-ordered superfluid state, our results serve as high-accuracy benchmarks for the coming generation of precision experiments with ultracold gases. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L13.00010: From 2D semimetal to topological Fulde-Ferrell superfluid in fermionic ultracold atoms Ting Fung Jeffrey Poon, Xiong-Jun Liu The intriguing topological phenomena have been observed in different condensed matter systems including topological insulators and topological supercondutors. In the light of this, the ultracold spin-orbit coupled Fermi gases became a excellent platform to investigate the phenomenon difficult to observe otherwise owing to its high experimental controllability. Since recent experiments have been able to realize two-dimensional spin-orbit coupling, the studies concerning topological superfluid are promising. In this work, we propose a generic theory to determine whether a time-reversal symmetry breaking system is topological or not after considering a superconducting pairing, by knowing the properties of the Fermi surfaces and the low lying states. Then we also propose an easily acheived experimental model that contains a novel 2D spin-orbit coupling for cold atoms to demonstrate the generic theory and to provide a possible realisation of a gapped topological Flude-Ferrell superflud, characterized by Cooper's pairs with finite center-of-mass momenta, with large topological regions. The Berezinskii Kosterlitz-Thouless transition in this system is also investigated in this work. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L13.00011: Four-dimensional semimetal in optical lattice Sen Niu, Songbo Wang, Xiong-Jun Liu We propose a realization of (3+1)-dimension semimetal using ultracold atoms in optical lattice. Based on a three dimensional (x, y, z) AIII class topological insulator with a bulk gap realized in three dimensional real space, we add one synthetic dimension (w direction) that consists of atomic internal states to close the gap and obtain a (3+1)D semimetal. The new type of unconventional Landau levels and novel quantum Hall effects in the present (3+1)D systems will be discussed. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L13.00012: Fractal chiral anomaly in cold atomic Weyls Michael Kolodrubetz, Sthitadhi Roy, Joel Moore, Adolfo Grushin The Hofstadter butterfly of lattice electrons in a strong magnetic field is a cornerstone of condensed matter physics, exploring the competition between periodicities imposed by the lattice and the field. In this talk we introduce and characterize the Weyl butterfly, which emerges when a large magnetic field is applied to a three-dimensional Weyl semimetal. Using an experimentally motivated lattice model for cold atomic systems, we solve this problem numerically. We find that Weyl nodes reemerge at commensurate fluxes and propose using wavepackets dynamics to reveal their chirality and location. Moreover, we show that the chiral anomaly -- a hallmark of the topological Weyl semimetal -- does not remain proportional to magnetic field at large fields, but rather inherits a fractal structure of linear regimes as a function of external field. The slope of each linear regime is determined by the difference of two Chern numbers in gaps of the Weyl butterfly and can be measured experimentally in time-of-flight. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L13.00013: Topological dynamics with highly non-degenerate modes Haitan Xu, David Mason, Luyao Jiang, Jack Harris Complex spectra of non-Hermitian systems may possess certain degenerate points called exceptional points, which give rise to nontrivial topological properties. Nonreciprocal topological dynamics has been experimentally demonstrated in an optomechanical system (Nature 537, 80 (2016)), where energy is transferred between two nearly degenerate mechanical modes by encircling an exceptional point. Here we use a novel approach to demonstrate non-reciprocal topological energy transfer between two highly non-degenerate modes. This approach can be applied in broad range of systems, and should greatly expand the forms of topological operation that can be accessed using exceptional points. [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L13.00014: Exact Excited States of the 1D AKLT Model Sanjay Moudgalya, Nicolas Regnault, B. Andrei Bernevig We analytically obtain an infinite series of exact excited states for the AKLT spin chain, a non-integrable model. These states can be interpreted as quasiparticles on the ground state or the ferromagnetic state and this is clear when written in terms of dimers. Some of these states are in the middle of the full energy spectrum. We compute the entanglement spectra of these states in both zero and finite energy density regimes, with implications to eigenstate thermalization. [Preview Abstract] |
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