  We demonstrate that for an ensemble of qudits, subjected to collective
decoherence in the form of perfectly correlated random SU(d) unitaries, quantum
superpositions stored in the decoherence free subspace are fully immune against
the removal of one particle. This provides a feasible scheme to protect quantum
information encoded in the polarization state of a sequence of photons against
both collective depolarization and one photon loss, and can be demonstrated
with photon quadruplets using currently available technology.
