Non-Hermitian physics uses gain and loss, rather than avoiding them, to create topological phenomena, usually in photonic lattices described by single-mode models. Real photonic resonators, however, often support several modes at each site. Elizabeth Louis Pereira and Jose Lado of QMAT's Correlated Quantum Materials group at Aalto University, with Hongwei Li and Andrea Blanco-Redondo, explore a family of multimodal non-Hermitian lattices.

They show that these lattices can host topological modes and criticality, analyse how robust the modes are to fluctuating losses, disorder and artificial gauge fields, and find that, thanks to their multiorbital nature, their localisation can be controlled by an external gauge field. Internal orbital degrees of freedom thus offer a way to engineer controllable non-Hermitian topology. Partners included the University of Central Florida.

Figure: Pereira et al., Phys. Rev. Research (2026); image from arXiv:2509.05163, CC BY 4.0