Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A51: Invited Session: Photonic and Driven Topological States |
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Sponsoring Units: DCMP Chair: Aditi Mitra, New York University Room: Grand Ballroom C1 |
Monday, March 2, 2015 8:00AM - 8:36AM |
A51.00001: Aspects of photonic topological insulators Invited Speaker: Mikael Rechtsman Great excitement surrounding optical topological protection has recently emerged from the promise of endowing photonic devices with quantum Hall-like robustness. Here, I will present the prediction and realization of a photonic topological insulator for light. Topological insulators (TIs) are solid-state materials that are insulators in the bulk, but conduct electricity along their surfaces - and are intrinsically robust to disorder. In particular, when a surface electron in a TI encounters a defect, it simply goes around it without scattering, always exhibiting -- quite strikingly -- perfect transmission. The structure is composed of an array of coupled helical waveguides; the helicity generates an artificial circularly-polarized force on the photons that breaks time-reversal symmetry. This leads to bands with non-zero Chern number, and thus topologically-protected edge states (protected in the quantum Hall sense -- not by any symmetry). Due to the time-dependent force, the band structure must be solved in the Floquet sense; the result bears close resemblance to that of the quantum anomalous Hall effect. I will also present experimental results on the first realization of a ``topological Anderson insulator'' (in a similar setting), where the addition of disorder can make a trivial system topological. Time permitting, I will discuss the question of what it means to have topological interface states in non-Hermitian systems, and show new experiments exploring their properties. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 9:12AM |
A51.00002: Proposed Realization and Signatures of Floquet Topological Superconductors and Insulators Invited Speaker: Babak Seradjeh As understood recently, a topological state may be generated dynamically in an otherwise normal combination of materials by a periodic driving force. These states can only occur when the system is driven out of equilibrium. A Floquet topological insulator can be realized, for example, in a two-dimensional system of Dirac fermions, such as graphene, irradiated by a circularly polarized laser [1]. It is characterized by steady state edge modes and \emph{two} separate integer-valued topological invariants. A Floquet topological superconductor, on the other hand, is characterized by two types of Floquet Majorana fermions---steady states of equal superposition of electrons and holes---with a period that is the same or twice that of the drive [2]. I introduce these concepts and present our recent theoretical work on the realization and detection of these Floquet topological states. First, I discuss how Floquet Majorana fermions can be realized in a highly tunable setup consisting of two coupled quantum dots and detected by a third probe dot [3]. More generally, Floquet Majorana fermions can be detected by measuring a quantized conductance sum rule over discrete values of lead bias differing by multiples of drive frequency [4]. This quantized sum rule is robust against weak disorder. Finally, I present an effective theory of Floquet topological insulators and use it to study their transport signature [5]. Remarkably, we find that disorder can enhance transport at certain Floquet topological transitions by several orders of magnitude. \\[4pt] [1] T. Oka, H. Aoki, Phys. Rev. B 79, 081406 (R) (2009).\\[0pt] [2] L. Jiang et al., Phys. Rev. Lett. 106, 220402 (2011).\\[0pt] [3] Y. Li, A. Kundu, F. Zhong, and B. Seradjeh, Phys. Phys. Rev. B 90, 121401(R) (2014).\\[0pt] [4] A. Kundu and B. Seradjeh, Phys. Rev. Lett. 111, 136402 (2013).\\[0pt] [5] A. Kundu, H. A. Fertig, and B. Seradjeh, Phys. Rev. Lett. (2014) in press; arXiv:1406.1490. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:48AM |
A51.00003: Interactions and dissipation in Floquet-Bloch systems Invited Speaker: Netanel Lindner Time periodic driving fields provide a versatile route for dynamically altering band structures. Particular excitement surrounds the possibility of controlling the topology of the resulting ``Floquet bands,'' whose topological classification is even richer than the one describing their static counterparts. While many schemes have been proposed for realizing interesting Floquet band structures, crucial questions remain regarding the many-body steady states of these systems. In this work we study the roles of interactions, heating, and dissipation in the population kinetics of many-particle Floquet systems. While a naive picture might lead one to expect rapid heating of any strongly driven interacting system, we find wide parameter regimes in which non-trivial Floquet steady states are obtained at intermediate and long times. Prospects for obtaining and probing the physics of these many-body Floquet systems will be discussed. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:24AM |
A51.00004: Topology in Floquet-Bloch systems: physics beyond the topological insulators Invited Speaker: Mark Rudner Floquet theory provides a powerful framework for understanding the dynamics of periodically-driven quantum systems. When applied to systems with spatially periodic potentials, the emergence of Floquet-Bloch quasienergy bands suggests many exciting opportunities to explore topological phenomena through analogies to those known in equilibrium. Due to the periodicity of quasienergy, however, the topological classification of periodically-driven systems is richer than that of static systems. This opens the way for discovering truly new, non-equilibrium topological phenomena. For example, a one dimensional Floquet system may host chiral bands, while in two dimensions a system whose Floquet bands all have zero Chern numbers may support robust chiral edge states. In this talk I will address the question: when is a Floquet-Bloch system {\it not} like a static system? I will discuss both general considerations, based on the structure of the time-dependent Floquet-Bloch evolution operator, and specific examples which highlight the possibilities available in both non-interacting and interacting systems. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 11:00AM |
A51.00005: Observation of topological transitions in interacting quantum circuits Invited Speaker: Pedram Roushan Topology, despite its mathematical abstractness, often manifests itself in physics and plays a pivotal role in our understanding of natural phenomena. Notable examples include the discoveries of topological phases in condensed matter systems which have changed the modern conception of phases of matter. The global nature of topological ordering, however, makes direct experimental probing an outstanding challenge. Present experimental tools are mainly indirect and inadequate for studying such properties at a fundamental level. Here, we employ the exquisite control afforded by superconducting quantum circuits to directly investigate topological properties of quantum spin systems. The essence of our approach is to infer local curvature by measuring the deflection of quantum trajectories topological properties are then revealed from a quantum analog of the Gauss-Bonnet theorem. We benchmark our technique by constructing the topological phase diagram of the celebrated Haldane model. The nature of the individual phases is revealed by visualizing their microscopic spin texture and evolution across the transition. Furthermore, we demonstrate the power of our method in studying the topology of interacting quantum systems, utilizing a novel qubit architecture which enables control over every term in a two-qubit Hamiltonian. We discovered an interaction-driven topological phase, whose emergence is understood by fully exploring the parameter-space of the Hamiltonian. Our work establishes a generalizable experimental platform to study fundamental aspects of topological phenomena in quantum systems. [Preview Abstract] |
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