Photonic quadrupole topological insulator using orbital-induced synthetic flux

Abstract

The rich physical properties of multiatomic molecules and crystalline structures are determined, to a significant extent, by the underlying geometry and connectivity of atomic orbitals. This orbital degree of freedom has also been used effectively to introduce structural diversity in a few synthetic materials including polariton lattices nonlinear photonic lattices and ultracold atoms in optical lattices. In particular, the mixing of orbitals with distinct parity representations, such as $s$ and $p$ orbitals, has been shown to be especially useful for generating systems that require alternating phase patterns, as with the sign of couplings within a lattice. Here we show that by further breaking the symmetries of such mixed-orbital lattices, it is possible to generate synthetic magnetic flux threading the lattice. This capability allows the generation of multipole higher-order topological phases in synthetic bosonic platforms, in which $\pi$ flux threading each plaquette of the lattice is required, and which to date have only been implemented using tailored connectivity patterns. We use this insight to experimentally demonstrate a quadrupole photonic topological insulator in a two-dimensional lattice of waveguides that leverage modes with both $s$ and $p$ orbital-type representations. We confirm the nontrivial quadrupole topology of the system by observing the presence of protected zero-dimensional states, which are spatially confined to the corners, and by confirming that these states sit at the band gap. Our approach is also applicable to a broader range of time-reversal-invariant synthetic materials that do not allow for tailored connectivity, e.g. with nanoscale geometries, and in which synthetic fluxes are essential.

References in corpus (11)

• Electric Multipole Moments, Topological Multipole Moment Pumping, and Chiral Hinge States in Crystalline Insulators
• Nearly-flat bands with nontrivial topology
• Visualization of higher-order topological insulating phases in two-dimensional dielectric photonic crystals
• Direct observation of corner states in second-order topological photonic crystal slabs
• Orbital superfluidity in the $P$-band of a bipartite optical square lattice
• Acoustic realization of quadrupole topological insulators
• Topological orbital ladders
• Experimental observation of Aharonov-Bohm caging using orbital angular momentum modes in optical waveguides
• Experimental observation of inter-orbital coupling
• Generalized Laws of Refraction and Reflection at Interfaces between Different Photonic Artificial Gauge Fields
• Perfect localization on flat band binary one-dimensional photonic lattices

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• Generalization of Benalcazar-Bernevig-Hughes model to arbitrary dimensions
• Dynamical Detection of Topological Spectral Density
• Probing Chiral-Symmetric Higher-Order Topological Insulators with Multipole Winding Number
• A mono-atomic orbital-based 1D topological crystalline insulator
• Nonlinear Switch and Spatial Lattice Solitons of Photonic s-p Orbitals
• Scattering theory of delicate topological insulators
• Topological Corner States in Bilayer and Trilayer Systems with Vertically Stacked Topological Heterostructures
• Light-Matter interactions in Hofstadter lattice with the next-nearest neighbor couplings
• Mixed higher-order topology and nodal and nodeless flat band topological phases in a superconducting multiorbital model
• Higher-Order Topological Systems and Their Sub-Symmetry-Protected Topology
• Flux-mediated effective Su-Schrieffer-Heeger model in an impurity decorated diamond chain
• Tunable corner states in topological insulators with long-range hoppings and diverse shapes
• Third-order Orbital Corner State and its Realization in Acoustic Crystals
• Impurity flat band states in the diamond chain
• Tunable cornerlike states in topological type-II hyperbolic lattices
• Orbital Frontiers: Harnessing Higher Modes in Photonic Simulators