  Trapping and storing light for arbitrary time lengths in open cavities is a
major goal of nanophotonics, with potential applications ranging from energy
harvesting to optical information processing. Unfortunately, however, the
resonance lifetime of conventional open resonators remains finite even in the
limit of vanishing material absorption, as a result of radiation loss. In this
context, bound states in the continuum (BiCs) have provided a unique way to
achieve unbounded resonance lifetimes despite the presence of compatible
radiation channels. However, physical constraints such as reciprocity,
linearity, and delay-bandwidth limits prevent the possibility to externally
excite such ideal bound states and make them interact with broadband sources.
Here, we overcome these limitations and theoretically demonstrate that
subwavelength open resonators undergoing a suitable temporal modulation can
efficiently capture a broadband incident wave into a nonradiating eigenmode of
the structure, leading to the first example of a BiC that is accessible to
broadband light. Our findings unveil the dynamic capabilities of bound states
in the continuum and extend their reach and potential impact for different
applications.
