A Schrödinger's cat state is detected in superconducting nanowires at high bias currents through the analysis of the statistics of the switching currents. It is demonstrated that at high bias currents the entire number of superconducting electrons in an ultrathin superconducting wire can quantum-mechanically tunnel from a state having a higher electrical current to one having a lower current. Since the effect involves a large number of electrons it is called macroscopic quantum tunneling (MQT). Another term used to describe such tunneling is "quantum phase slip" (QPS). Unlike in previous reports on superconducting nanowires, here the conclusion about the presence of QPS is reached by measuring and analyzing the fluctuation of the switching current at T=0.3 K.

M. Sahu, M.-H. Bae, A. Rogachev, D. Pekker, T.-C. Wei, N. Shah, P. M. Goldbart and A. Bezryadin, Nature Physics 5, 503 (2009).

Image courtesy: Dr. A. Bezryadin, UIUC.