  We show how to realize a ``protected'' qubit by using a fully frustrated
Josephson Junction ladder (JJL) with Mobius boundary conditions. Such a system
has been recently studied within a twisted conformal field theory (CFT)
approach (Mod. Phys. Lett. A 15 (2000) 1679; Nucl. Phys. B 641 (2002) 547) and
shown to develop the phenomenon of flux fractionalization (Eur. Phys. J. B 49
(2006) 83). The relevance of a ``closed'' geometry has been fully exploited in
relating the topological properties of the ground state of the system to the
presence of half flux quanta and the emergence of a topological order has been
predicted (JSTAT (2005) P03006). In this letter the stability and
transformation properties of the ground states under adiabatic magnetic flux
change are analyzed and the deep consequences on the realization of a solid
state qubit, protected from decoherence, are presented.
