Low-loss Traveling-Wave Parametric Amplifier without Dispersion Engineering*

We discuss theoretical and experimental results about a novel architecture of Traveling-Wave Amplifier (TWPA), based on an array of coupled asymmetric SQUIDs which allows for phase matching a four-wave mixing process for efficient parametric amplification. Unique to this design is that the nonlinear 3rd order term in the energy phase relation is suppressed as the 4th order Kerr coefficient can be tuned with a magnetic flux over a wide range and even change sign. The change in sign of the Kerr non-linearity can be exploited along with the chromatic dispersion of the TWPA for phase matching of a four-wave mixing process without the need for introducing dispersion engineering resonant elements which prohibit a tunable pump frequency, introduce gain ripples, and result in a stop-band in the middle of the gain bandwidth. The design allows for tunability of the characteristic impedance of the TWPA as well as reduced sensitivity of amplifier performance to fabrication tolerances in Josephson junctions. We will present preliminary results of TWPAs fabricated with low-loss dielectrics which show low insertion loss, sufficient gain, wide bandwidth and discuss pump depletion effects due to the generation of higher harmonics.