Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R01: Topological States in AMO Systems IIFocus
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Sponsoring Units: DAMOP DCMP Chair: Justin Wilson, Rutgers University Room: 103 |
Thursday, March 5, 2020 8:00AM - 8:36AM |
R01.00001: Non-Hermitian topological photonics and light steering Invited Speaker: Liang Feng Photonic topological insulators provide a route for disorder-immune light transport, which holds promise for practical applications. Flexible reconfiguration of topological light pathways can enable high-density photonics routing, thus sustaining the growing demand for data capacity. By strategically interfacing non-Hermitian and topological physics, we demonstrate arbitrary, robust light steering in reconfigurable non-Hermitian junctions, in which chiral topological states can propagate at an interface of the gain and loss domains. Our non-Hermitian–controlled topological state can enable the dynamic control of robust transmission links of light inside the bulk, fully using the entire footprint of a photonic |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R01.00002: Floquet engineering with resonant drive and Application to symmetry-protected topological phases Kaoru Mizuta, Kazuaki Takasan, Norio Kawakami Recently periodically driven (Floquet) systems have attracted much interested, and Floquet engineering, control of phases by a periodic drive, is one of the most vigorous fields in Floquet systems. However, in conventional Floquet engineering, only high-frequency drives (=drives whose energy scale is much smaller than the frequency) are mainly utilized since it is based on high-frequency expansion theory, only applicable to Floquet systems under high-frequency drives. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R01.00003: Topological amplification in photonic lattices and the classification of topological non-Hermitian phases Diego Porras, Samuel Fernández-Lorenzo A proper characterization of non-trivial topological phases in dissipative systems is highly non-trivial. This is the case of photonic lattices, superconducting circuits or even vibronic systems like trapped ions, whose description typically involves the eigenstates of a non-Hermitian coupling matrix, H. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R01.00004: Topological Invariants for Quantum Quench Dynamics Haiping Hu, Erhai Zhao Quantum quench is nonequilibrium dynamics and its interplay with band topology gives rise to intriguing dynamical topological phenomena. We introduce the concept of loop unitary $$U_l$$ and its homotopy invariant $$W_3$$ to fully characterize the quench dynamics of arbitrary two-band insulators in two dimensions, going beyond existing scheme based on Hopf invariant which is only valid for trivial initial states. The theory traces the origin of nontrivial dynamical topology to the emergence of $$\pi$$-defects in the phase band of $$U_l$$, and establishes that $$W_3=C_f-C_i$$, i.e. the Chern number change across the quench. We further show that the dynamical singularity is also encoded in the winding of the eigenvectors of $$U_l$$ along a lower dimensional curve where dynamical quantum phase transition occurs, if the pre- or post-quench Hamiltonian is trivial. The winding along this curve is related to the Hopf link, and shown to give rise to torus links and knots for quench to Hamiltonians with Dirac points. Our framework which can be generalized to multiband systems and other dimensions paves the way to study quench dynamics and its associated topology. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R01.00005: Quantum many-body scars from virtual entangled pairs Sambuddha Chattopadhyay, Hannes Pichler, Mikhail Lukin, Wen Wei Ho We study weak ergodicity breaking in a one-dimensional, non-integrable spin-1 XY model. We construct for it an exact highly excited eigenstate, which despite having a non-zero energy density, can be represented analytically by a finite bond-dimension matrix product state (MPS) with area-law entanglement. Upon a quench to a finite Zeeman field, the state undergoes periodic dynamics with perfect many-body revivals, in stark contrast to other generic initial states which instead rapidly thermalize. Remarkably, we find that the dynamics can be completely understood in terms of the evolution of entangled virtual spin-1/2 degrees of freedom, which in turn underpin the presence of an O(L) tower of strong-eigenstate thermalization hypothesis (ETH)-violating many-body eigenstates: quantum many-body scars. The scars we find are therefore of novel origin, and we provide insight into their nature and entanglement structure. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R01.00006: Haldane Phase in Spin-1 Bose-Hubbard Model with Flat Band Hong Yang, Hayate Nakano, Hosho Katsura The Haldane phase has been widely discussed in spin chains. A famous rigorous example is the AKLT model. However, in itinerant spin systems which have both unfrozen spin and charge degrees of freedom, the Haldane phase has been rarely investigated, to say nothing of any rigorous results. Here we study the spin-1 Bose-Hubbard model on a sawtooth lattice with flat band. At half-unit filling with fine-tuned interaction strength, we prove that the ground state can be exactly written down in the form of a matrix product state (MPS) similar to that of the AKLT model. The ground state correlation lengths, edge states, string order parameters, etc. are analytically given for both spin and charge degrees of freedom. The entanglement spectrum also analytically shows perfect two-fold degeneracy. Moreover, with general interaction strength, when a parameter (related to hopping and on-site potential of the lattice) is sufficiently large, perturbation theory yields the spin-1 bilinear-biquadratic model as the effective spin model, which can be either symmetry-protected-topological (Haldane) or trivial, depending on the interaction strength. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R01.00007: Detecting fractional Chern insulators in optical lattices through quantized displacement Ilyoun Na, Johannes Motruk The realization of interacting topological states of matter such as fractional Chern insulators (FCIs) in optical lattices with synthetic gauge fields has recently come within experimental reach. However, detecting their occurrence might prove difficult since transport measurements akin to those in solid state systems are challenging to perform in cold atom setups and alternatives have to be found. We consider a ν = 1/2 FCI state realized in the lowest band of a Harper-Hofstadter model of hardcore bosons in a harmonic trapping potential. We demonstrate the stability of the topological state for a wide range of confining strengths by density matrix renormalization group simulations. Using matrix-product state algorithms, we study the time evolution when applying an effective electric field for the particles on top of the harmonic confinement. The movement of the particle cloud allows an accurate determination of the fractionally quantized Hall conductivity which provides an experimentally measurable signal to detect the topological nature of the state. Below a critical field strength, the particle displacement shows oscillations around the quantized value which abate as the field strength decreases. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R01.00008: Robustness of quantum scarred states to the presence of disorder and external drives Ian Mondragon-Shem, Maxim G Vavilov, Ivar Martin Recent experiments in Rydberg atom quantum simulators have found unexpected coherent and persistent oscillations in an ergodic system at infinite temperature. The origin of such oscillations has been explained in terms of quantum scarred states that are embedded in an ergodic spectrum. We examine the robustness of such quantum scarred states to the presence of inhomogeneous potentials as well as the action of external drives. We focus on models that exhibit approximate SU(2) symmetries, such as the PXP model, and explore conditions under which the dynamics of the system remains non-ergodic. To do this, we evaluate diagnostic quantities such as the revival probability, the spatial entanglement, and the average spin dynamics. Finally, we discuss similarities with the disordered Heisenberg spin chain in a regime in which anomalous non-ergodic dynamics can also be obtained. |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R01.00009: Topological effects in interacting Su-Schrieffer-Heeger chains Helena Drueeke, Dieter Bauer The Su-Schrieffer-Heeger (SSH) model [1] describes a linear chain with two distinct topological phases. We investigate the behavior of two interacting particles in this one-dimensional system by simulating the equivalent system of a single particle in a two-dimensional system. Even though the two particles repel each other, doublon states, where both particles are on the same lattice site, are possible. By performing time-dependent simulations, we investigate transitions between the two topological phases of the two-dimensional SSH-like system. We focus on the doublon and surface states and the relation between them. |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R01.00010: Topological photonic resonator for chiral quantum optics Sabyasachi Barik, Aziz Karasahin, Sunil Mittal, Edo Waks, Mohammad Hafezi Topological photonics has enabled unprecedented applications in the field of optics. The resulting topological structures exhibit chiral edge states that are robust to disorder and sharp bends. By coupling these photonic states to quantum emitters, one can generate directional light emission. Even though the previous works have investigated directional light emission in one-dimensional edge states, the extension of this concept to resonator structures has remained elusive. Here we demonstrate chiral light-matter interactions in a topological resonator. We use valley-Hall topological edge states to realize a helical resonator. Such a helical resonator is created at the interface of two distinct topological regions that supports two counter-propagating light modes with opposite polarizations. We show the chiral coupling of the resonator to a quantum emitter. Moreover, we achieve an intensity enhancement of 3.4 due to resonant coupling. Such robust resonators could provide a platform for studying novel many-body dynamics and designing complex nano-photonic circuits. |
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R01.00011: Effective field theories at the edges of topological insulators Manuel Valiente, Xin Chen We consider interacting two-dimensional time reversal invariant topological insulators with time reversal preserving (non-magnetic) disorder near their edges. These systems are known to fail to exhibit quantized spin currents even when the fermion-fermion interactions are weak, as was recently shown within Hartree-Fock theory (Novelli et al., Phys. Rev. Lett. 122, 016601). Here, we investigate the microscopic origin of the lack of quantization by considering the most relevant few-body processes at the edges of the system, and find that fermion-impurity resonances are responsible for backscattering. We build two different effective field theories for the interacting edge modes in the system near the Fermi energy that eliminate the bulk in two different ways: 1) by keeping the inhomogeneity explicitly and 2) by accounting for the width of the resonance in the dispersion relations. |
Thursday, March 5, 2020 10:24AM - 10:36AM |
R01.00012: Dynamical Quantum Phase Transitions in U(1) Quantum Link Models in (1+1)d and (2+1)d Yi-Ping Huang, Debasish Banerjee, Markus Heyl Quantum link models (QLMs) are extensions of Wilson-type lattice gauge theories which realize exact gauge invariance with finite-dimensional Hilbert spaces. QLMs not only reproduce standard features of Wilson lattice gauge theories in equilibrium, but can also host new phenomena such as crystalline confined phases. The local constraints due to gauge invariance also provide kinetic restrictions that can influence substantially the real-time dynamics in these systems. We aim to characterize the nonequilibrium evolution in lattice gauge theories through the lens of dynamical quantum phase transitions, which provide general principles for real-time dynamics in quantum many-body systems. Specifically, we study quantum quenches for two representative cases, U(1) QLMs in (1+1)D and (2+1)D, for initial conditions exhibiting long-range order. Finally, we discuss the connection to the high-energy perspective and the experimental feasibility to observe the discussed phenomena in recent quantum simulator settings such as trapped ions, ultracold atoms, and Rydberg atoms. |
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