  Three-wave mixing is a key process in superconducting quantum information
processing, being involved in quantum-limited amplification and parametric
coupling between superconducting cavities. These operations can be implemented
by SNAIL-based devices that present a Kerr-free flux-bias point where unwanted
parasitic effects such as Stark shift are suppressed. However, with a single
flux-bias parameter, these circuits can only host one Kerr-free point, limiting
the range of their applications. In this Letter, we demonstrate how to overcome
this constraint with a gradiometric SNAIL, a doubly-flux biased superconducting
circuit for which both effective inductance and Kerr coefficient can be
independently tuned. Experimental data show the capability of the gradiometric
SNAIL to suppress Kerr effect in a three-wave mixing parametric amplifier over
a continuum of flux bias points corresponding to a 1.7 GHz range of operating
frequencies.
