Pole-vaulting superconductors: How rare current fluctuations push a superconductor over the edge.

In their paper, "Stochastic dynamics of a Josephson junction threshold detector", Sukhorukov and Jordan solve a long-standing problem in theoretical physics.  The problem is to predict the escape rate of a particle in a meta-stable potential, subject to random driving noise chosen from an arbitrary probability distribution.  This process plays an important role in various fields from astrophysics to the solid-state.  In many physical cases, a simple Gaussian noise model is sufficient, whose celebrated solution was given by Kramers in 1940.  While the author's solution to this problem is quite general, they focus on a particular system of current experimental investigation: a nanoscale electrical conductor in a circuit containing a superconducting "Josephson junction".  As the electrons travel through the circuit, they act as a noise source driving the Josephson junction (the meta-stable system).  Much like a pole-vault, if a current fluctuation exceeds a given value, the Josephson junction is driven out of its superconducting state, and into a normal-conducting state. By observing how often this transition occurs, the Josephson junction acts as a threshold detector, mapping out the statistics of single-electron current.  Such a system has recently been realized by an experimental group in Finland, and a preprint is available [ arXiv:cond-mat/0612087 ].  The challenge of undertaking this experiment has only very recently become possible.