Casimir Stress Concentration.

Casimir force, stemming from quantum fluctuation prominent at nanoscale, can cause notable motion or deformation of objects. While Casimir-induced rigid-body motion has been successfully described, quantifying elastic deformation remains challenging due to the poorly understood Casimir stress. By advancing a dedicated boundary element method, we find the Casimir stress concentration similar to the classical mechanics counterpart. Using a wedge-plate system as a prototype, we show that the Casimir stress on wedge slope exerted by a noncontacting plate is concentrated near the vertex, exceeding the pressure predicted by proximity-force approximation by orders of magnitude. Such an effect is attributed to the disrupted principal Maxwell stress trajectories by geometric singularity. Both the transformation optics analysis and the normalized stress distribution indicate a scale invariance of the Casimir stress. This Letter not only highlights the significant geometric effect on Casimir stress but also facilitates Casimir-based elastic mechanics.