  We report the parametric amplification of a microwave signal in a Kerr medium
formed from superconducting qubits. Two mutually coupled flux qubits, embedded
in the current antinode of a superconducting coplanar waveguide resonator, are
used as a nonlinear element. Shared Josephson junctions provide the
qubit-resonator coupling, resulting in a device with a measured gain of about
20 dB. We argue, that this arrangement represents a unit cell which can be
straightforwardly extended to a quasi one-dimensional quantum metamaterial with
a large tunable Kerr nonlinearity.
