Diffractive Orbits in an Open Microwave Billiard

We demonstrate experimentally the existence and significance of diffractive orbits in an open microwave billiard. Orbits that diffract off a sharp edge strongly influence the conduction spectrum, especially in the regime where there are no stable classical orbits. On resonance, the wave functions are influenced by both classical and diffractive orbits. Off resonance, the wave functions are determined by the constructive interference of multiple transient orbits. The experimental results agree well with quantum computations and with a semiclassical theory that incorporates diffraction.