  We study the effect of Kerr nonlinearity in quantum thermal machines having a
Kerr-nonlinear oscillator as working substance and operating under the ideal
quantum Otto cycle. We first investigate the efficiency of a Kerr-nonlinear
heat engine and show that by varying the Kerr-nonlinear strength the efficiency
surpasses in up to 2.5 times the efficiency of a quantum harmonic oscillator
Otto engine. Moreover, the Kerr-nonlinearity makes the coefficient of
performance of the Kerr-nonlinear refrigerator to be as large as 3 times the
performance of quantum harmonic oscillator Otto refrigerators. These results
were obtained using realistic parameters from circuit quantum electrodynamics
devices formed by superconducting circuits and operating in the microwave
regime.
