  We have developed a concept for a traveling-wave parametric amplifier driven
by a magnetic flux wave. The circuit consists of a serial array of symmetric dc
SQUIDs coupled inductively to a separate superconducting LC transmission line
carrying the pump microwave; thereby the signal and pump are applied to
different ports. The proposed three-wave-mixing amplifier includes, firstly, an
adjustable phase velocity of the signal (idler) wave and hence good phase
matching yielding large gain in a wide frequency range and, secondly,
overcoming of the pump depletion problem. The experimental parameters and
characteristics of this amplifier have been evaluated and show promise for
applications in quantum-information single-photon circuits.
