  We demonstrate a quadratic phase gate for one-way quantum computation in the
continuous-variable regime. This canonical gate, together with phase-space
displacements and Fourier rotations, completes the set of universal gates for
realizing any single-mode Gaussian transformation such as arbitrary squeezing.
As opposed to previous implementations of measurement-based squeezers, the
current gate is fully controlled by the local oscillator phase of the homodyne
detector. Verifying this controllability, we give an experimental demonstration
of the principles of one-way quantum computation over continuous variables.
Moreover, we can observe sub-shot-noise quadrature variances in the output
states, confirming that nonclassical states are created through cluster
computation.
