If the field is strong enough, however, some of the external field lines will be able to penetrate the superconductor, although only by organizing themselves into flux bundles (also called vortices) of discrete sizes. That is, the bundles are commonly thought to possess a flux in multiples of a basic unit equal to Planck's constant divided by 2 times the charge of the electron. Decades ago theorists pointed out that this is indeed the case for flux bundles deep inside superconductors but not for bundles near the boundary of the sample. Now researchers at the University of Nijmegen in Holland (Andre Geim, geim@sci.kun.nl) and the University of Antwerp in Belgium have demonstrated this experimentally, verifying that some flux vortices do not encompass quantum values of the basic unit of magnetism; indeed some vortices have but a tiny fraction (as small as 1%) of the unit value. (Geim et al., Nature, 7 September 2000; for experimental background, also see Geim et al., Physical Review Letters, 14 September 2000.
In summary, the making of C12H10 molecules from C6H5I molecules, normally carried out on a copper catalyst and using thermal activation (a process chemists call the Ullmann reaction), has here been forced to proceed by employing one molecule at a time at a cryogenic temperature of 20 K. The researchers believe that new manmade molecules, never before seen in nature, can be engineered in this way, including the selective detachment or replacement of parts of larger molecules for individual assembling of molecular based nano-devices. (Hla et al., Physical Review Letters, 25 Sept; Select Articles.)
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 2000; Select Articles.)