Kerr nonlinearities and nonclassical states with superconducting qubits and nanomechanical resonators

We propose the use of a superconducting charge qubit capacitively coupled to two resonant nanomechanical resonators to generate Yurke-Stoler states, i.e., quantum superpositions of pairs of distinguishable coherent states 180° out of phase with each other. This is achieved by effectively implementing Kerr nonlinearities induced through the application of a strong external driving field in one of the resonators. A simple study of the effect of dissipation on our scheme is also presented and lower bounds of fidelity and purity of the generated state are calculated. Our procedure to implement a Kerr nonlinearity in this system may be used for high-precision measurements in nanomechanical resonators.