Strongly nonlinear kinetic inductance resonators with titanium nitride nanowires

Thin films of disordered superconductors, such as titanium nitride (TiN), exhibit large kinetic inductance (KI), high critical temperature, and low loss in the single-photon regime. The intrinsic Kerr nonlinearity of these films has been previously exploited for microwave parametric conversion, amplification, and detection. These experiments operate in the regime of weak nonlinearity, where dissipation rates exceed the strength of the self-Kerr nonlinearity by several orders of magnitude. Here, we report strongly nonlinear TiN resonators based on a compact nanowire geometry, with a small inductive mode volume V = 10 x 40 x 800 nm³. We characterize the nonlinearity of the fabricated resonators in the single-photon regime using two-tone spectroscopy and report a single-photon Kerr shift to linewidth ratio of 8%. With improved fabrication, our devices are expected to reach the regime of strong quantum nonlinearity, with the potential for junction-free quantum circuits based on KI thin films.