Environmentally-induced exceptional points in elastodynamics.

We study the nature of an environment-induced exceptional point in a non-Hermitian pair of coupled mechanical oscillators. The mechanical oscillators are a pair of pillars carved out of a single isotropic elastodynamic medium made of aluminum and consist of carefully controlled differential losses. The inter-oscillator coupling originates exclusively from background modes associated with the "environment", that portion of the structure which, if perfectly rigid, would support the oscillators without coupling. We describe the effective interaction in terms of a coupled mode framework where only one nearby environmental mode can qualitatively reproduce changes to the exceptional point characteristics. Our experimental and numerical demonstrations illustrates new directions utilizing environmental mode control for the implementation of exceptional point degeneracies. Potential applications include a new type of non-invasive, dfferential atomic force microscopy and hypersensitive sensors for the structural integrity of surfaces.