Salient point: the diffraction limit, sets in when the distance between two objects is equal to half the wavelength of the light used for imaging. The wavelength in the middle of the colour spectrum is about 500 nanometres. That means the pixels in a printed image can’t be spaced any closer together than about 250 nanometres without looking smudged. Yang’s images pack the pixels at just this distance.

Hence, "ultimate resolution".