Reconstructing Josephson Current-Phase Relations with Intermodulation Spectroscopy

When driving with multiple tones, a nonlinear system will give rise to intermodulation, or frequency mixing. Two drive tones placed near a nonlinear resonance produces a comb of intermodulation products. We present a method based on matrix inversion to reconstruct the nonlinearity from a measurement of this comb [1, 2]. We apply this method to a microwave frequency comb generated from a Nb-coplanar waveguide resonator with Josephson weak-links. This method is useful for accurate characterization of nonlinearities in superconducting quantum circuits.

[1] Hutter et al., PRL 104, 050801 (2010)
[2] Platz et. al., Beilstein J. Nanotechnol., 4, 352–360 (2013)