  An invisible cavity is an open resonant device that confines a localized
field without producing any scattering outside of the device volume. By
exploiting the scatter-less property of such device, it is possible to nest two
invisible cavities, as the outer cavity would simply not notice the presence of
the inner one, regardless of their relative position. As a result, the position
of the inner cavity becomes a means to easily control the field localized
inside the cavity and its quality factor. In this paper, we discuss the
properties of nested invisible cavities as a simple method to achieve stronger
localized fields and high tunable quality factor. Furthermore, we show that in
optics, these cavities can be implemented using nanodisk-based dielectric
metasurfaces that operate near their electric resonances.
