Confining light in deep subwavelength electromagnetic cavities

We demonstrate that it is possible to confine electromagnetic radiation in cavities that are significantly smaller than the wavelength of the radiation it encapsulates. To this aim, we use the techniques of transformation optics. First, we present a "perfect cavity" of arbitrarily small size in which such confined modes can exist. Furthermore, we show that these eigenmodes have a continuous spectrum and that bending losses are absent, in contrast to what is observed in traditional microcavities. Finally, we introduce an alternative cavity configuration that is less sensitive to material imperfections and still exhibits deep subwavelength modes combined with high quality factor, even if considerable material losses are included. Such a cavity may be interesting for the storage of information in optical data processing and for applications in quantum optics.