  We investigate hyperfine-induced decoherence in a triangular spin-cluster for
different qubit encodings. Electrically controllable eigenstates of spin
chirality (C_z) show decoherence times that approach milliseconds, two orders
of magnitude longer than those estimated for the eigenstates of the total spin
projection (S_z) and of the partial spin sum (S_{12}). The robustness of
chirality is due to its decoupling from both the total- and individual-spin
components in the cluster. This results in a suppression of the effective
interaction between C_z and the nuclear spin bath.
