  We have studied the low-energy excitations in a minimalistic protected
Josephson circuit which contains two basic elements (rhombi) characterized by
the $\pi$ periodicity of the Josephson energy. Novel design of these elements,
which reduces their sensitivity to the offset charge fluctuations, has been
employed. We have observed that the life time $T_{1}$ of the first excited
state of this quantum circuit in the protected regime is increased up to $70\mu
s$, a factor of $\sim100$ longer than that in the unprotected state. The
quality factor $\omega_{01}T_{1}$ of this qubit exceeds $10^{6}$ . Our results
are in agreement with theoretical expectations; they demonstrate the
feasibility of symmetry protection in the rhombi-based qubits fabricated with
existing technology.

Superconductivity;Mesoscale and Nanoscale Physics