  In measurement-based quantum computing an algorithm is performed by
measurements on highly-entangled resource states. To date, several
implementations were demonstrated, all of them assuming perfect noise-free
environments. Here we consider measurement-based information processing in the
presence of noise and demonstrate quantum error detection. We implement the
protocol using a four-qubit photonic cluster state, where we first encode a
general qubit non-locally such that phase errors can be detected. We then read
out the error syndrome and analyze the output states after decoding. Our
demonstration shows a building block for measurement-based quantum computing
which is crucial for realistic scenarios.
