A 5-nm-wide carbon nanotube bundle, or "rope," is probed by gold electrical contacts. Pairs of single nanotubes might be used in future experiments to separate the entangled electron pairs in superconductors. Image credit: Paul L. McEuen/Cornell Univ.
Entangled pairs of particles, in which measuring the state of one simultaneously determines the state of the other, are a central part of proposed schemes for quantum cryptography and teleportation. One potential source of such particles is the stream of conjoined electrons that exist in superconductors, but no one has been able to drive a wedge between these so-called Cooper pairs. A recent proposal suggests one possible separation method: send them down a pair of carbon nanotubes. Experimenters may have the technology needed for such an experiment in a few years.