Coherent quantum phase slip

TL;DR

This paper reports the first experimental observation of coherent quantum phase slip (CQPS) in a disordered superconducting wire, demonstrating a phenomenon previously only theorized, with potential implications for quantum technology.

Contribution

The study provides the first direct experimental evidence of CQPS in a strongly disordered superconductor, confirming a fundamental quantum phenomenon predicted a century ago.

Findings

Observation of superposition of quantum flux states

Demonstration of CQPS in disordered indium-oxide wire

Potential for new superconducting quantum devices

Abstract

A hundred years after discovery of superconductivity, one fundamental prediction of the theory, the coherent quantum phase slip (CQPS), has not been observed. CQPS is a phenomenon exactly dual to the Josephson effect: whilst the latter is a coherent transfer of charges between superconducting contacts, the former is a coherent transfer of vortices or fluxes across a superconducting wire. In contrast to previously reported observations of incoherent phase slip, the CQPS has been only a subject of theoretical study. 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 in the vicinity of the superconductor-insulator transition (SIT). Here we report the first direct observation of the CQPS in a strongly disordered indium-oxide (InOx) superconducting wire inserted in a loop, which is manifested by the superposition of the quantum states with different number of fluxes. Similarly to the Josephson effect, our observation is expected to lead to novel applications in superconducting electronics and quantum metrology.