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Regular version of the site

Article

Coherent quantum phase slip

Nature. 2012. Vol.  484. No. 7394. P. 355-358.
Arutyunov, K.Y., Astafiev O. V., Ioffe L., Kafanov S., Pashkin Y., Shahar D., Cohen O., Tsai J.

A hundred years after the discovery of superconductivity, one
fundamental prediction of the theory, coherent quantum phase
slip (CQPS), has not been observed. CQPS is a phenomenon exactly
dual1 to the Josephson effect; whereas the latter is a coherent
transfer of charges between superconducting leads2,3, the former
is a coherent transfer of vortices or fluxes across a superconducting
wire. In contrast to previously reported observations4–8 of incoherent
phase slip, CQPS has been only a subject of theoretical
study9–12. Its experimental demonstration is made difficult by
quasiparticle dissipation due to gapless excitations in nanowires or
in vortex cores. This difficulty might be overcome by using certain
strongly disordered superconductors near the superconductor–
insulator transition. Here we report direct observation of CQPS in
a narrow segment of a superconducting loop made of strongly disordered
indium oxide; the effect is made manifest through the
superposition of quantum states with different numbers of flux
quanta13. As with the Josephson effect, our observation should lead
to new applications in superconducting electronics and quantum
metrology1,10,11