  Classical, interferometric, optical lithography is diffraction limited to
writing features of a size lambda/2 or greater, where lambda is the optical
wavelength. Using nonclassical photon number states, entangled N at a time, we
show that it is possible to write features of minimum size lambda/(2N) in an
N-photon absorbing substrate. This result surpasses the usual classical
diffraction limit by a factor of N. Since the number of features that can be
etched on a two-dimensional surface scales inversely as the square of the
feature size, this allows one to write a factor of N^2 more elements on a
semiconductor chip. A factor of N = 2 can be achieved easily with entangled
photon pairs generated from optical parametric downconversion. It is shown how
to write arbitrary 2D patterns by using this method.

Quantum Physics