Continuous-variable square-ladder cluster states in a microwave frequency comb

We demonstrate the experimental realization of three independent, square-ladder, continuous variable cluster states between 95 modes of a microwave frequency comb. The result is obtained by injecting vacuum fluctuations properly thermalized at 10mK into a Josephson Parametric Amplifier parametrically pumped by three coherent signals around double the center-comb frequency. We reach up to 1dB of squeezing of the cluster state's nullifiers. We compare the nullifier squeezing with the maximum quadrature squeezing reachable by our setup for both cases of one and three parametric pumps and find reasonable agreement.