  Noiseless subsystems offer a general and efficient method for protecting
quantum information in the presence of noise that has symmetry properties. A
paradigmatic class of error models displaying non-trivial symmetries emerges
under collective noise behavior, which implies a permutationally-invariant
interaction between the system and the environment. We describe experiments
demonstrating the preservation of a bit of quantum information encoded in a
three qubit noiseless subsystem for general collective noise. A complete set of
input states is used to determine the super-operator for the implemented
one-qubit process and to confirm that the fidelity of entanglement is improved
for a large, non-commutative set of engineered errors. To date, this is the
largest set of error operators that has been successfully corrected for by any
quantum code.
