  We discuss the implementation of an iterative quantum phase estimation
algorithm, with a single ancillary qubit. We suggest using this algorithm as a
benchmark for multi-qubit implementations. Furthermore we describe in detail
the smallest possible realization, using only two qubits, and exemplify with a
superconducting circuit. We discuss the robustness of the algorithm in the
presence of gate errors, and show that 7 bits of precision is obtainable, even
with very limited gate accuracies.
