  Great interest revolves around the development of new strategies to
efficiently store and manipulate quantum information in a robust and
decoherence-free fashion. Several proposals have been put forward to encode
information into qubits that are simultaneously insensitive to relaxation and
to dephasing processes. Among all, given their versatility and high degree of
control, superconducting qubits have been largely investigated in this
direction. Here, we present a survey on the basic concepts and ideas behind the
implementation of novel superconducting circuits with intrinsic protection
against decoherence at a hardware level. In particular, the main focus is on
multi-mode superconducting circuits, the paradigmatic example being the
so-called $0-\pi$ circuit. We report on their working principle and possible
physical implementations based on conventional Josephson elements, presenting
recent experimental realizations, discussing both fabrication methods and
characterizations.
