  We developed and experimentally tested a Symmetric Traveling Wave Parametric
Amplifier (STWPA) based on Three-Wave Mixing, using the new concept of a
Symmetric rf- SQUID. This allows to fully control the second and third order
nonlinearities of the STWPA by applying external currents. In this way, the
optimal bias point can be reached, taking into account both phase mismatch and
pump depletion minimization. The structure was tested at 4.2K, showing a 4GHz
bandwidth and a maximum estimated gain of 17dB. STWPA showed also great
flexibility, allowing up-down conversion mixer operations and rf-controlled
switch.
