The coherent quantum phase-slip nanowire (QPSNW) is predicted to be the precise dual of the Josephson junction. Coherent tunnelling of fluxons across the nanowire leads to a sinusoidal relationship between the voltage and charge.

We have performed a systematic series of experiments in which a niobium nitride QPSNW incorporated in a superconducting loop is inductively coupled to an r.f. coplanar waveguide (CPW) resonator [1]. By controlling the thickness of our sputtered NbN in the sub-20 nm range the films lie close to the superconductor-insulator transition while the internal quality factor of the CPW resonators exceed 100,000. We demonstrate that the number of fluxons tunnelling across the nanowire can be controlled with single fluxon accuracy. We further give evidence of coherent coupling between the resonator and a two-level system and discuss the implications of this measurement in the context of coherent quantum phase slip.

This work is supported by the EPSRC through grants EP/P510270/1 and EP/J017329/1.

[1] Potter, J. A. et al. IEEE Trans. Appl. Supercond. 30 1100704 (2020)