Quantum Mechanics puts a limit on how small the degradation of information passing through an amplifier can be. It is known theoretically that the minimum noise added by an "op-amp"-like amplifier to the signal amounts at least to half a photon at the signal frequency. Can we develop a practical amplifier working at microwave frequencies that would approach this quantum limit? We will present a new type of amplifier which is based on a ring of four Josephson tunnel junction. Unlike the SQUID, which is powered by a DC source, our amplifier is powered by an RF source, and its backaction noise is minimal. Our results [1] can immediately be applied to the readout of solid state qubits, and, on a longer time scale, to the measurement of very weak signals in various areas of science.