ONTOP

Project title: On‐demand Non‐hermitian TOPology

Funding Scheme: H2020-MSCA-IF-2018 (Marie Skłodowska-Curie Individual Fellowships)

Grant Agreement number: 840745

Physical materials can display a topological order, i.e. a collective organisation characterised by a discrete number or “topological charge”. Because the integer nature of this charge must be preserved throughout the structure, topological order is intrinsically immune to perturbations and the system is said to be topologically protected. Recently, the replication of topological protection in optics has raised the interest of the scientific community for its potential ability to overcome fundamental problems—like the influence of imperfections intrinsically present in nanoscale-fabrication processes, which currently preclude the development of multiple photonic technologies. Yet, at optical frequencies the weak response of materials often precludes a topological approach such that even careful designs can only partially deliver the expected protection. In contrast to material properties, gain and loss can be easily manipulated in optics. While the exploitation of nonhermitian systems—with non-conserved energy—recently enabled the formation of topological order in wave physics, it simultaneously questioned our theoretical understanding of topology and offered a large variety of new degrees of freedom that are yet to be explored.


In this action, I suggested exploiting the versatility of optical gain-loss to imprint topological order “on-demand” onto otherwise topologically trivial systems. Through non-uniform spatial distributions of optical gain and loss, I demonstrated theoretically the formation of topological protection in random systems. In sharp contrast with the conventional conception of topology that relies on careful and rigid designs, this project emphasised the possibility to engineer topology through external control. Throughout the course of this action, similar control have been experimentally implemented to harness the properties of optical systems, such as the light emitted by THz lasing sources. In this way, this project offered a paradigmatic change that will enable the development of new photonic devices, whose properties can be controlled and reconfigured “on-demand”.


Research training

  • Remote numerical calculations: Courses focusing on high-performance cluster computing.

  • Writing of grant applications for junior researchers such as ERC starting packages.

  • Accepted to the school "Waves in Complex Media WACO school 2020" (Les Houches, France) for a training on light propagation through complex systems (canceled due to Covid)

  • Planned registration to the school "Topological Matter School 2020" (San Sebastian, Spain) for a training on topology (canceled due to Covid)


Scientific production

  1. Sebastian Schönhuber, Nicolas Bachelard, Benedikt Limbacher, Martin Kainz, Aaron Andrews, Hermann Detz, Gottfried Strasser, Juraj Darmo, Stefan Rotter and Karl Unterrainer. ”All-Optical Adaptive Control of Quantum Cascade Random Lasers.”, Nature Communications 11(1), 1-8 (2020).

  2. Markus Kaczvinszki, Nicolas Bachelard, Jakob Hüpfl, Michael Horodynski, Matthias Kühmayer and Stefan Rotter, “Optimal Cooling of Multiple Levitated Particles through Far-Field Wavefront-Shaping”, under review in Physical Review Letters arXiv:2103.12592.

  3. Benedikt Limbacher, Sebastian Schönhuber, Martian Alexander Kainz, Nicolas Bachelard, Aaron Maxwell Andrews, Herman Detz, Gottfried Strasser, Juraj Darmo and Karl Unterrainer, “Deep Learning Control of THz QCLs”, under review in Optics Express.

  4. Nicolas Bachelard and Stefan Rotter, “Controlling topological order in random media”, in preparation.


Oral Conference Presentations and dissemination

  1. "DIEP Workshop: Topology and broken symmetries", Utrecht (The Netherlands), July 2019 (Invited)

  2. “PIERS 2019”, Rome (Italy), June 2021 (Invited)

  3. ”Complex Nanophotonics Science Camp”, Windsor Park (United Kingdom), August 2019 (Invited)

  4. ”Waves in Disordered Media Workshop”, Boulder CO (USA), Marche 2020

  5. News coverage (Austrian Press Agency, Chemie.de and Analytica News).

This project has received funding support from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie (MSCA) grant agreement No. 840745. All research work, payments, travel, and management actions have been carried out in compliance with the "Agreement for implementing research training activities for MSCA single-beneficiary projects" between the researcher and the Technical University of Vienna. Gender does not apply to the questions addressed in this proposal.