Coherent Perfect Absorption in Chaotic Microwave Graphs*

Coherent perfect absorption (CPA) has been of great interest to the physics community, in part because it represents the time-reversed version of a laser. The CPA process works by taking waves of particular amplitude and phase (coherent illumination) from multiple input channels and causing them to interfere and to be completely absorbed by losses in the system. Its implementation promises the realization of a novel family of extremely efficient absorbers, tunable and highly-selective notch filters, and high-efficiency energy conversion systems. We experimentally demonstrate the concept of coherent perfect absorption in a microwave graph constructed from coaxial cables connected by Tee-junctions. By adding a simple variable lossy attenuator into the system, we can effectively identify the CPA frequencies as the complex zeros of the scattering matrix which crosses the real axis and achieve perfect absorption in this chaotic setup. Most importantly, our experimental set-up allows us to demonstrate that the concept of CPA can be extended beyond the case where time-reversal (TR) symmetry holds, by introducing a circulator into the microwave graph.