  The difference between the phases of superconducting order parameter plays in
superconducting circuits the role similar to that played by the electrostatic
potential difference required to drive a current in conventional circuits. This
fundamental property can be altered by inserting in a superconducting circuit a
particular type of weak link, the so-called Josephson $\pi$-junction having
inverted current-phase relation and enabling a shift of the phase by $\pi$. We
demonstrate the operation of three superconducting circuits -- two of them are
classical and one quantum -- which all utilize such $\pi$-phase shifters
realized using superconductor-ferromagnet-superconductor sandwich technology.
The classical circuits are based on single-flux-quantum cells, which are shown
to be scalable and compatible with conventional niobium-based superconducting
electronics. The quantum circuit is a $\pi$-phase biased qubit, for which we
observe coherent Rabi oscillations and compare the measured coherence time with
that of conventional superconducting phase qubits.
