title: Experimental observation of anomalous topological edge modes in a slowly driven photonic lattice.
abstract: Topological quantum matter can be realized by subjecting engineered systems to time-periodic modulations. In analogy with static systems, periodically driven quantum matter can be topologically classified by topological invariants, whose non-zero value guarantees the presence of robust edge modes. In the high-frequency limit of the drive, topology is described by standard topological invariants, such as Chern numbers. Away from this limit, these topological numbers become irrelevant, and novel topological invariants must be introduced to capture topological edge transport. The corresponding edge modes were coined anomalous topological edge modes, to highlight their intriguing origin. Here we demonstrate the experimental observation of these topological edge modes in a 2D photonic lattice, where these propagating edge states are shown to coexist with a quasi-localized bulk. Our work opens an exciting route for the exploration of topological physics in time-modulated systems operating away from the high-frequency regime.
authors.affiliation: Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Sebabrata
authors.initials: S
authors.lastname: Mukherjee
authors.affiliation: Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Alexander
authors.initials: A
authors.lastname: Spracklen
authors.affiliation: Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Manuel
authors.initials: M
authors.lastname: Valiente
authors.affiliation: Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Erika
authors.initials: E
authors.lastname: Andersson
authors.affiliation: Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Patrik
authors.initials: P
authors.lastname: Öhberg
authors.affiliation: Center for Nonlinear Phenomena and Complex Systems, Université Libre de Bruxelles, CP 231, Campus Plaine, B-1050 Brussels, Belgium.
authors.forename: Nathan
authors.initials: N
authors.lastname: Goldman
authors.affiliation: Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences (IPaQS), Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Robert R
authors.initials: RR
authors.lastname: Thomson