ENTANGLED PHOTONS CAN DEFEAT THE DIFFRACTION LIMIT, a new paper suggests. This might lead to a much sharper form of microchip lithography than is possible with "classical" photons. The factor that ordinarily determines how small a standard lithography technique can write features on a chip is known as the diffraction limit, or Rayleigh criterion, which says that you can't inscribe a feature, or see a detail, smaller than half the wavelength of the light or other radiation used to perform the task.

But new research (Jonathan Dowling, JPL/Caltech, 818-393-5343, Jonathan.P.Dowling@jpl.nasa.gov) shows that the Rayleigh criterion applies to classical physics but not quantum physics. In their proposal for "quantum interferometric lithography," two entangled photons enter a setup containing mirrors and beamsplitters. The two photons--acting as a single unit--constitute a light wave which is split up and then recombined on a surface, creating patterns on the surface equivalent to those that would be made by a single photon with half the wavelength. On a 2-D surface, this would allow researchers to write features four times smaller than prescribed by the Rayleigh limit.

Preparing three entangled photons (still more difficult) and sending them through the device would create even better results: effectively a single photon with a third of the wavelength, enabling nine-fold smaller features on a 2-D surface. Although more work is needed to realize this proposal, the technique potentially allows the creation of features smaller than 25 nm, the size limit below which classical computer designs would begin to fail because of phenomena such as electron tunneling. (Boto et al., Physical Review Letters, 25 Sept /pnu/2000/; Select Articles.)