WSi weak link element with a non-sinusoidal current-phase relation

TL;DR

This paper demonstrates the nonlinear behavior of a tungsten silicide constriction embedded in a 3D RF-SQUID, consistent with a weak link acting as a Josephson junction with a non-sinusoidal current-phase relation, and measures relaxation times of metastable states.

Contribution

It introduces a novel weak link element with a non-sinusoidal current-phase relation, expanding the understanding of nonlinear quantum circuit components.

Findings

The weak link behaves as a Josephson junction with a sawtooth-like current-phase relation.

Relaxation times of metastable states are measured.

Results are consistent with quantum phase slip behavior.

Abstract

Nonlinearity is an essential ingredient for encoding quantum states with non-uniform energy spacing, implementing coherent quantum gates, reading out qubits, amplifying, and mixing electromagnetic signals. In this work, we demonstrate the nonlinear behavior of a constriction fabricated from an amorphous, high-kinetic inductance material, tungsten silicide, embedded in a three-dimensional RF-SQUID. We find that the results are consistent with the weak link behaving as a Josephson junction with a sawtooth-like current-phase relation or a quantum phase slip element. Finally, we measure relaxation times of the metastable, persistent-current states trapped in the local minima of the potential.