Bulletin of the American Physical Society
2023 APS March Meeting
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D66: Topological States in AMO Systems IFocus Session
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Sponsoring Units: DAMOP Chair: Ying Su, University of Texas at Dallas Room: Room 413 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D66.00001: Recent advanced in topological photonics Invited Speaker: Mohammad Hafezi We discuss our recent advances in topological photonics. First, we report our progress in investigating the nonlinear optical properties of topological ring resonators. Then, we show various topological phenomena in fiber loops by temporal multiplexing. In the end, we discuss the topological interplay between photons and electrons. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D66.00002: Non-Abelian Floquet braiding and anomalous Dirac string phase in periodically driven systems Robert-Jan Slager, Adrien Bouhon, Nur Unal Topological phases of matter span a wide area of research shaping fundamental pursuits and offering promise for future applications. While a significant fraction of topological materials has been characterized using symmetry requirements of wave functions, the past two years have witnessed the rise of novel multi-gap dependent topological states, the properties of which go beyond these approaches and are yet to be fully explored. Thriving upon these insights, we report on uncharted anomalous phases and properties that can only arise in out-of-equilibrium Floquet settings. In particular, we identify Floquet-induced non-Abelian braiding mechanisms, which in turn lead to a phase characterized by an anomalous Euler class, the prime example of a multi-gap topological invariant. Most strikingly, we also retrieve the first example of an `anomalous Dirac string phase'. This gapped out-of-equilibrium phase features an unconventional Dirac string configuration that physically manifests itself via anomalous edge states on the boundary. Our results therefore not only provide a stepping stone for the exploration of intrinsically dynamical and experimentally viable multi-gap topological phases, but also demonstrate a powerful way to observe these non-Abelian processes notably in quantum simulators. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D66.00003: Identifying topological markers in gapless photonic systems with topological phase transitions at an interface Kahlil Y Dixon Photonic topological insulators exhibit bulk-boundary correspondence, which requires that boundary-localized states appear at the interface between topologically distinct insulating materials. However, in many topological photonic systems, this raises a subtle problem, as free-space is gapless for photons above the light-line. Although experiments have observed localized photonic edge states in this regime, their topology has been defined using theories which effectively approximate free-space to be insulating. Here, we show that even at the interface between a gapless material and a topological insulator these systems still exhibit both a topological phase transition and bulk-boundary correspondence. To do so, we employ the system's spectral localizer, which uses a system’s real-space description to calculate local topological markers and local topological protection independent of the material’s bulk band gap (or lack thereof). Ultimately, we show that topological photonic crystals can still demonstrate topological behavior and associated edge localizer resonances while in contact with free-space or any other gapless media. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D66.00004: Polaritonic Chern insulators in monolayer semiconductors Li He, Jingda Wu, Jicheng Jin, Eugene J Mele, Bo Zhen Systems with strong light-matter interaction opens up new avenues for studying topological phases of matter. Examples include exciton-polaritons, mixed light-matter quasiparticles, where the topology of the polaritonic band structure arises from the collective coupling between matter wave and optical fields strongly confined in periodic dielectric structures. Distinct from light-matter interaction in a uniform environment, the spatially varying nature of the optical fields leads to a fundamental modification of the well-known optical selection rules, which were derived under the plane wave approximation. Here we identify polaritonic Chern insulators by coupling valley excitons in transition metal dichalcogenides to photonic Bloch modes in a dielectric photonic crystal slab. We show that polaritonic Dirac points, which are markers for topological phase transition points, can be constructed from the collective coupling between valley excitons and photonic Dirac cones in the presence of both time-reversal and inversion symmetries. Lifting exciton valley degeneracy by breaking time-reversal symmetry leads to gapped polaritonic bands with non-zero Chern numbers. Through numerical simulations, we predict polaritonic chiral edge states residing inside the topological gaps. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D66.00005: Disordered topological graphs enhancing nonlinear phenomena Zhetao Jia, Matteo Seclì, Alexander Avdoshkin, Walid Redjem, Elizabeth Dresselhaus, Joel E Moore, Boubacar Kante Since their discovery in crystalline materials, topological insulators have also been realized in amorphous solids, where non-trivial topology is captured by the real space version of the Chern number. Unlike the periodic lattice, disorder in amorphous structure induces Anderson localization of the bulk modes. We propose and demonstrate topological structurally disordered systems with a modal structure that enhances nonlinear phenomena by inhibiting the leakage of energy from topological edge modes to bulk modes in the presence of nonlinearities. We present the construction of the graph and show that its dynamics enhances the photon pair generation rate in an optical realization. [1] |
Monday, March 6, 2023 4:24PM - 4:36PM |
D66.00006: Topological control of light with graphene devices Coskun Kocabas The topological structure associated with the branchpoint singularity around an exceptional point (EP) can provide tools for controlling the propagation of light. Using graphene-based devices, we demonstrate the emergence of EPs in the electrically controlled interaction of light with a collection of organic molecules in the terahertz regime at room temperature. We show that the intensity and phase of terahertz pulses can be controlled by a gate voltage which drives the device across the EP. Our electrically tuneable system allows reconstructing the Riemann surface associated with the complex energy landscape and provides a topological control of light by tuning the loss-imbalance and frequency detuning of interacting modes. Our approach provides a platform for developing topological optoelectronics and studying the manifestations of EP physics in light-matter interactions. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D66.00007: Second Euler number in four-dimensional synthetic matter Giandomenico Palumbo, Robert-Jan Slager, Adrien Bouhon, Yan-Qing Zhu Two-dimensional Euler insulators are novel kind of spinless fermionic systems that support topological phases, which exhibit a quantised first Euler number in their bulk. This topological invariant is protected by the spacetime inversion symmetry. Recently, these phases have been experimentally realised in suitable two-dimensional synthetic matter setups. Artificial engineered systems, ranging from ultracold atoms to photonics and electric circuits, offer the unique way to implement higher-dimensional phases that cannot exist in real quantum materials. Although the second Euler invariant is a familiar invariant in both differential topology (Gauss-Bonnet theorem) and in four-dimensional Euclidean gravity, its existence in synthetic matter has never been explored so far. In this talk, we firstly introduce and describe two specific novel models in four dimensions that support a non-zero second Euler number in the bulk together with peculiar gapless boundary states. Secondly, we discuss its robustness in general spacetime-inversion invariant phases and its role in the classification of topological degenerate real bands through real Grassmannians. Finally, we show how to engineer these new topological phases in a four-dimensional ultracold atom setup. Our results naturally generalize the second Chern and spin Chern numbers to the case of four-dimensional phases that are characterised by real Hamiltonians. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D66.00008: Topological phases of driven-dissipative lattices: non-Hermitian physics and experimental implementations Diego Porras, Tomas Ramos, Alejandro Gonzalez-Tudela, Álvaro Gómez-León
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Monday, March 6, 2023 5:00PM - 5:12PM |
D66.00009: Loss-driven topological transitions in lasing from quasi-BIC in plasmonic lattices Grazia Salerno, Paivi E Torma Plasmonic lattices of metal nanoparticles have emerged as an effective platform for strong light-matter coupling, lasing, and Bose-Einstein condensation. However, the full potential of complex unit cell structures has not been exploited. On the other hand, bound states in continuum (BICs) have attracted attention, as they provide topologically protected optical modes with diverging quality factors. We show that nanoparticle lattices with complex unit cells enable lasing in quasi-BIC modes with a exceedingly high quality Q factor. By combining theory with polarization-resolved measurements of the emission, we show that the lasing mode has a non-trivial polarization winding, which changes when tuning the scale of the unit cell. By a theoretical analysis we identify the lasing modes as quasi bound states in continuum (quasi-BICs) of topological charges of zero, one or two. A T-matrix simulation of the structure reveals that the mode Q factors depend on the scale of the unit cell, with highest-Q modes favored by lasing. The system thus shows a loss-driven transition between lasing in modes of trivial and high-order topological charge.
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Monday, March 6, 2023 5:12PM - 5:24PM |
D66.00010: Single-mode robust defect-based laser Fargol Seifollahi, Abouzar Gharajeh, Qing Gu, Hamidreza Ramezani Non-Hermitian systems can exhibit unique topological effects that can be realized in photonic crystals, metamaterials, and coupled resonators. In our theoretical and experimental work, by utilizing non-Hermitian degeneracies known as the exceptional points (EP) and a locally embedded defect in a trivial array of microring resonators, we form a single-mode robust defect-based laser emission that is immune from disorder in the couplings in the array. Our proposed design facilitates going beyond edge mode lasing and bypasses the requirements sought to be evaded in previous approaches towards achieving topological lasing modes. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D66.00011: Dynamical Degeneracy Splitting and Directional Invisibility in Non-Hermitian Systems Kai Zhang The non-Hermitian skin effect (NHSE) refers to extensive bulk modes localized at the open boundaries, which makes the energy spectra and wave functions sensitive to the change in boundary conditions. In higher dimensions, the geometry-dependent skin effect has recently been proposed, i.e., the NHSE disappears in some specified open-boundary geometries but reappears in generic open-boundary geometries. Although theoretically, the geometry-dependent skin effect can universally exist in higher-dimensional non-Hermitian systems, a detectable signature experimentally is still lacking. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D66.00012: Topological multi-mode waveguide QED Alejandro Gonzalez-Tudela, Diego Porras, Carlos Vega, Alberto Muñoz de las Heras Two-dimensional topological insulators with quantized large Chern numbers feature a number of protected, chiral edge modes linked to the value of the invariant. When implemented in photonic setups, these systems then naturally display a topologically-protected multi-mode waveguide at their edges. Here, we show how to take advantage of these setups by interfacing them with quantum emitters. Using a Harper-Hofstadter lattice as a particular model, we find situations in which the emitters feature quasi-quantized decay rates due to the increasing number of edge modes in the different emergent band-gaps, and where their spontaneous emission spatially separates in different modes, enabling the generation of non-local time-bin entangled states already with a single π-pulse. Besides, we show how the emitters can selectively interact with the different channels using non-local light-matter couplings as the ones that can be obtained with giant atoms. Such capabilities pave the way for generating quantum gates among topologically-protected photons as well as generating more complex entangled states of light in topological channels. |
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