  Non-Hermitian wave engineering has attracted a surge of interest in photonics
in recent years. One of the prominent phenomena is coherent perfect absorption
(CPA), in which the annihilation of electromagnetic scattering occurs by
destructive interference of multiple incident waves. This concept has been
implemented in various platforms to demonstrate real-time control of
absorption, scattering and radiation by varying the relative phase of the
excitation signals. However, so far these studies have been limited to simple
photonic systems involving single or few modes at well-defined resonant
frequencies. Realizing CPA in more complex photonic systems is challenging
because it typically requires engineering the interplay of a large number of
resonances featuring large spatial complexity within a narrow frequency range.
Here, we extend the paradigm of coherent control of light to a complex photonic
system involving more than 1,000 optical modes in a chaotic microresonator. We
efficiently model the optical fields within a quasi-normal mode (QNM)
expansion, and experimentally demonstrate chaotic CPA states, as well as their
non-Hermitian degeneracies, which we leverage to efficiently control the cavity
excitation through the input phases of multiple excitation channels. Our
results shed light on the universality of non-Hermitian physics beyond simple
resonant systems, paving the way for new opportunities in the science and
technology of complex nanophotonic systems by chaotic wave interference.
