Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W33: Topological States in AMO SystemsFocus Recordings Available
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Sponsoring Units: DAMOP DCMP Chair: Nur Unal, University of Cambridge Room: McCormick Place W-192C |
Thursday, March 17, 2022 3:00PM - 3:12PM |
W33.00001: tightly focused polychromatic knots Manuel F Ferrer, Alessio D'Errico, Hugo Larocque, Alicia Sit, Ebrahim Karimi The use of structured light has allowed the realization of complex structures with rich topological features. In recent years, it has been shown that the field’s dislocations can form closed trajectories as they propagate, tracing knotted curves in a three-dimensional volume. Following these results, we raise a fundamental question: is it possible to knot the curves traced by the electric field as it evolves over time? In contrast to the case of monochromatic light, the vast “zoo” of polarization states of polychromatic fields remains almost unexplored. In this work, we aim to study the behavior of structured polychromatic light when they are tightly focused by high numerical aperture lenses. Here, we follow a heuristic approach to generate regions of knotted polarization curves on the focal plane based on the knowledge of the tight focusing of vector vortex beams. Our results may provide insight into the potential experimental realization of these new exotic and complex polarization states using current techniques developed for nonlinear and nanophotonics. In addition, these locally knotted fields may find applications in the field of light-matter interaction where the nontrivial topological structure could induce local magnetic fields in semiconductors. |
Thursday, March 17, 2022 3:12PM - 3:24PM |
W33.00002: Quantum interference of topological states in a pumped Su-Schrieffer-Heeger lattice Zengzhao Li, Juan Atalaya, Birgitta Whaley We propose a realization of topological quantum interference in a pumped non-Hermitian Su-Schrieffer-Heeger (SSH) lattice that can be implemented by creation and coherent control of excitonic states of trapped neutral atoms. Our approach is based on quenching the system from the topological to the gapless phase and then back again, by switching the value of the laser phase controlling the lattice potential. We find interference patterns following switching in the occupation probabilities of excitations on lattice sites. These occur both as many-excitation interferences in the presence of pumping, and interferences seen in the absence of pumping when starting with edge excitations. Investigation of the excitation dynamics shows that these interference patterns which originate from the topological nature of the initial states, are very different from interferences originating from non-topological states of the lattice. Our results also reveal that unlike well-known situations where topological states are protected against local perturbations, in these non-Hermitian SSH systems a local dissipation at each lattice site can suppress both the topological interference and the total population of the lattice. |
Thursday, March 17, 2022 3:24PM - 3:36PM |
W33.00003: Topologically protected vortex knots Toni Annala, Roberto A Zamora-Zamora, Mikko Mottonen As Lord Kelvin noted in a 1869 article, knotted vortex lines in an ideal fluid will remain forever knotted. However, the same is not true in non-idealized systems, as viscous flows may violate the conservation of knottedness. Here we investigate a version of vortex knot stability that holds for knots tied in the order parameter fields of certain condensed-matter systems. In our setting, the stability of a knot is a consequence of the nontrivial interaction between the knotting type of the vortex line and the topology of the corresponding order parameter space. We expect these results to be rather robust, as they are topological in nature, and therefore immune against local perturbations. We give concrete physical examples of this behavior, focusing mostly on spinor Bose--Einstein condensates. |
Thursday, March 17, 2022 3:36PM - 4:12PM |
W33.00004: Floquet engineering topological Dirac bands Invited Speaker: Ian Spielman We experimentally realize a time-periodically modulated 1D lattice for ultracold atoms featuring a pair of linear bands, each protected by a Floquet winding number, a topological invariant. These bands are spin-momentum locked and almost perfectly linear everywhere in the Brillouin zone (BZ), making this system a near-ideal realization of the 1D Dirac Hamiltonian. We characterized the Floquet winding number using a form of quantum state tomography\delete{, covering the BZ and following the micromotion in one Floquet period}. |
Thursday, March 17, 2022 4:12PM - 4:24PM |
W33.00005: Topological phases with periodically kicked molecules Volker Karle, Areg Ghazaryan, Mikhail Lemeshko In the last decade technological advances have made possible unprecedented coherent manipulation of molecules. Improved control of the duration and temporal shape of laser pulses opens up new possibilities to create platforms for quantum simulation and information processing. In our work we propose to use molecules kicked by lasers as a non-hermitian topological system to probe topological modes. We utilize the polarization of the laser and the asymmetry of the molecule as additional degrees of freedom to realize topological phases and transitions between them. In particular, we show that using an elliptically polarized laser creates an effective two-dimensional lattice with non-trivial states at the boundary (analogous to chiral states for a hermitian chiral system). The explored theoretical models are experimentally feasible with the current techniques. This makes it possible to utilize these systems as building blocks for quantum computation with a higher level of control than in traditional solid state based systems. |
Thursday, March 17, 2022 4:24PM - 4:36PM |
W33.00006: Floquet quadrupole photonic crystals protected by space-time symmetry Jicheng Jin, Li He, Jian Lu, Eugene J Mele, Bo Zhen Quadrupole topological insulators with nontrivial and quantized second-order moments, which can protect zero-dimensional corner states two dimensions lower than the bulk, are potentially useful in optoelectronic applications. So far, such quadrupole phases are studied in lattice models with synthetic symmetries or patterned dielectric medium with spatial symmetries. In this work, we present a Floquet quadrupole topological insulator in a nonlinear photonic crystal. The nontrivial quadrupole phase is protected and quantized by a space-time screw symmetry. This symmetry is induced by both the nonlinear susceptibilities of the material and the external driving field. We confirm the quantized second-order moment by both symmetry indices analysis and numerical calculations of the nested-Wilson loop. Key features including fractional occupation and filling anomalies are observed. |
Thursday, March 17, 2022 4:36PM - 4:48PM |
W33.00007: Z2 Topological Photonics for Robust Transport in the Visible Spectrum Pufan Liu, Hongfei Zeng, David Czaplewski, Nathaniel P Stern Topological photonics aims to realize optical analogs of topological states of matter using photonic circuits. Since topological edge states are protected from defect scattering, quantum superpositions generated by strong light-matter interactions can be transferred without loss by photons in a topological photonic circuit. However, there are so far very few studies of light-matter interactions in topological photonics due to the mismatch between topological photonic circuit designs and promising materials for integrating with them. In this work, we propose and demonstrate a novel topological photonic structure together with an overetch procedure that can open a complete optical band gap in the visible spectral region using low index contrast materials. Devices following this design have been fabricated and evaluated via transmission and imaging experiments. These results demonstrate the existence of topological edge states with this design and the robustness of edge states against scattering. This topological photonics design is suitable for integrating with visible-wavelength materials with minimal fabrication challenges. |
Thursday, March 17, 2022 4:48PM - 5:00PM |
W33.00008: Majorana bosons: Searching for symmetry-protected topological phases in quasi-free bosonic systems Vincent P Flynn, Emilio Cobanera, Lorenza Viola Despite the ubiquity of quasi-free bosonic systems in condensed-matter, atomic, molecular, and optical physics, their ability to exhibit symmetry-protected topological phases remains elusive. While it is well known that such phases are forbidden in closed, stable, bosonic matter, we uncover potential signatures in the form of 'Majorana bosons' in quasi-free systems undergoing Markovian dissipation. By leveraging tools from pseudospectral analysis, we show that Majorana bosons exist over a transient timescale which increases with system size. This 'topological metastability' is unique to bosons and is associated with a robust topological invariant. Each Majorana boson pair consists, in general, of a distinct zero mode and a symmetry generator, reflecting the absence of a Noether-like theorem in open quantum dynamics. We argue that Majorana bosons will result in distinctive zero-frequency peaks in steady-state observable power spectra. |
Thursday, March 17, 2022 5:00PM - 5:12PM |
W33.00009: Fractional Chern insulators in coupled chains Felix Alexander A Palm, Fabian Grusdt, Ulrich J Schollwoeck The study of fractional quantum Hall states, and in particular their exotic anyonic excitations, poses a major challenge in current research. In particular, cold atoms in optical lattices provide a promising platform to realize and manipulate fractional Chern insulators in the very near future. Inspired by the success of coupled wire constructions in the continuum, we here discuss a possible route to realization starting from weakly coupled chains in the context of a Hofstadter-Bose-Hubbard model. Performing DMRG calculations, we gain insight into both analytically meaningful quantities (like the central charge or the many-body Chern number) and experimentally accessible observables (like chiral edge currents or on-site correlations). While Luttinger liquid physics dominates in the decoupled limit, close to the isotropic limit we find a topologically non-trivial phase showing signatures of the Laughlin state at filling factor ν = 1/2. This approach is expected to generalize to other filling factors and can be used to develop new adiabatic preparation schemes. |
Thursday, March 17, 2022 5:12PM - 5:24PM |
W33.00010: Symmetry-Protected Topological Phases in a Rydberg Glass Kai Li, Jionghao Wang, Yanbin Yang, Yong Xu Recent study predicts that structural disorder, serving as a bridge connecting a crystalline material to an amorphous material, can induce a topological insulator from a trivial phase. However, to experimentally observe such a topological phase transition is very challenging due to the difficulty in controlling structural disorder in a quantum material. Given experimental realization of randomly positioned Rydberg atoms, such a system is naturally suited to studying structural disorder induced topological phase transitions and topological amorphous phases. Motivated by the development, we study topological phases in an experimentally accessible one-dimensional amorphous Rydberg atom chain with random atom configurations. In the single-particle level, we find symmetry-protected topological amorphous insulators and a structural disorder induced topological phase transition, indicating that Rydberg atoms provide an ideal platform to experimentally observe the phenomenon using state-of-the-art technologies. Furthermore, we predict the existence of a gapless symmetry-protected topological phase of interacting bosons in the experimentally accessible system. The resultant many-body topological amorphous phase is characterized by a Z2 invariant and the density distribution. |
Thursday, March 17, 2022 5:24PM - 5:36PM |
W33.00011: Topological quantum critical points in the extended Bose-Hubbard model Luca Barbiero The combination of topology and quantum criticality can give rise to an exotic mix of counterintuitive effects. Here, we show that unexpected topological properties take place in a paradigmatic strongly-correlated Hamiltonian: the 1D extended Bose-Hubbard model. In particular, we reveal the presence of two distinct topological quantum critical points with localized edge states and gapless bulk excitations. Our results show that the topological critical points separate two phases, one topologically protected and the other topologically trivial, both characterized by a long-range ordered string correlation function. The long-range order persists also at the topological critical points and it reflects the presence of localized edge states protected by a finite charge gap. Finally, we introduce a super-resolution quantum gas microscopy scheme for dipolar dysprosium atoms, which provides a reliable route towards the experimental study of topological quantum critical points. |
Thursday, March 17, 2022 5:36PM - 5:48PM |
W33.00012: Quantized transport of solitons in nonlinear Thouless pumps: From Wannier drags to topological polarons Nathan Goldman, Nader Mostaan, Fabian Grusdt Recent progress in synthetic lattice systems has opened the door to novel explorations of topological matter. In particular, photonics devices and ultracold matter waves offer the unique possibility of studying the rich interplay between topological band structures and tunable nonlinearities. In this emerging field of nonlinear topological physics, a recent experiment [Nature 596, 63 (2021)] revealed the quantized motion of localized nonlinear excitations, known as solitons, upon driving a Thouless pump sequence; the reported results suggest that the quantized displacement of solitons is dictated by the Chern number of the band from which they emanate. In this work, we elucidate the origin of this nonlinear topological effect, by showing that the motion of solitons is established by the quantized displacement of Wannier functions. Furthermore, we consider the quantum-mechanical parent of this setting and relate the quantized motion of solitons to the transport of Bose polarons (dressed impurities). By demonstrating the quantized pumping of Bose polarons, our work introduces a novel instance of topological polaron, which could be observed in ultracold atomic mixtures. |
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