Quantum interferometric optical lithography: exploiting entanglement to beat the diffraction limit

*Physical Review Letters* **85**, 2733 (2000)

Classical, interferometric, optical lithography is diffraction limited to writing features of a size l/4 or greater, where l is the optical wavelength. Using non-classical photon-number states, entangled N at a time, we show that it is possible to write features of minimum size l/(4N) 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 NxN more elements on a semiconductor chip. A factor of N=2 can be achieved easily with entangled photon pairs generated from optical parametric down-conversion.