Direct Measurement of a Non-Hermitian Topological Invariant in a Hybrid Light-Matter System

Understand

Topology is central to understanding and engineering materials that display robust physical phenomena immune to imperfections.

• Different topological phases of matter are characterised by topological invariants.
• In energy-conserving (Hermitian) systems, these invariants are determined by the winding of eigenstates in momentum space.
• In non-Hermitian systems, a novel topological invariant is predicted to emerge from the winding of the complex eigenenergies.