  Chaos is a phenomenon that occurs in many aspects of contemporary science. In
classical dynamics, chaos is defined as a hypersensitivity to initial
conditions. The presence of chaos is often unwanted, as it introduces
unpredictability, which makes it difficult to predict or explain experimental
results. Conversely, we demonstrate here how chaos can be used to enhance the
ability of an optical resonator to store energy. We combine analytic theory
with ab-initio simulations and experiments in photonic crystal resonators to
show that a chaotic resonator can store six times more energy than its
classical counterpart of the same volume. We explain the observed increase with
the equipartition of energy among all degrees of freedom of the chaotic
resonator, i.e. the cavity modes, which is evident from the convergence of
their lifetime towards a single value. A compelling illustration of the theory
is provided by demonstrating enhanced absorption in deformed polystyrene
microspheres.
