  Measurement-based quantum computation with optical time-domain multiplexing
is a promising method to realize a quantum computer from the viewpoint of
scalability. Fault tolerance and universality are also realizable by preparing
appropriate resource quantum states and electro-optical feedforward that is
altered based on measurement results. While a linear feedforward has been
realized and become a common experimental technique, nonlinear feedforward was
unrealized until now. In this paper, we demonstrate that a fast and flexible
nonlinear feedforward realizes the essential measurement required for
fault-tolerant and universal quantum computation. Using non-Gaussian ancillary
states we observed 10$\%$ reduction of the measurement excess noise relative to
classical vacuum ancilla.
