  Achieving the very special condition of perfect absorption (PA) in a complex
scattering enclosure promises to enable a wealth of applications in secure
communication, precision sensing, wireless power transfer, analog signal
processing and random lasing. Consequently, a lot of recent research effort was
dedicated to proposing wave-front shaping protocols to implement coherent PA in
a complex scattering environment. Here, instead of shaping the impinging wave
front and tuning the system's attenuation, we propose the conceptually
different route of solely tweaking the randomness of the complex scattering
environment in order to achieve PA. We provide an experimental proof-of-concept
in the microwave domain where we tune the randomness of a three-dimensional
chaotic cavity with a programmable metasurface. We systematically investigate
the achievability and extreme sensitivity of the PA condition. Our technique
can impose a PA condition at over hundred distinct frequencies within a small
frequency band, which allows us to propose and experimentally demonstrate a
concrete practical application: receiver-powered secure wireless communication
in a complex scattering enclosure. Our fundamentally new perspective on PA is
applicable to all types of wave phenomena and our results foreshadow the large
potential of this novel tool for minute wave control in sensing, communication
and energy transfer.
