Four-mode continuous-variable (CV) cluster states are an important and necessary resource in continuous-variable quantum computation. In this paper, we present a simple and efficient scheme to realize an unequally weighted four-mode square CV cluster state using atomic ensembles driven by seven strong classical laser fields. The scheme requires just a single selection of the appropriate squeezing parameters and pump laser parameters. With the unique squeezing operator and a new unitary transformation, we show that seven laser fields drive four atomic ensembles into a ...
