  We have developed a recently proposed Josephson traveling-wave parametric
amplifier with three-wave mixing [A. B. Zorin, Phys. Rev. Applied 6, 034006,
2016]. The amplifier consists of a microwave transmission line formed by a
serial array of nonhysteretic one-junction SQUIDs. These SQUIDs are flux-biased
in a way that the phase drops across the Josephson junctions are equal to 90
degrees and the persistent currents in the SQUID loops are equal to the
Josephson critical current values. Such a one-dimensional metamaterial
possesses a maximal quadratic nonlinearity and zero cubic (Kerr) nonlinearity.
This property allows phase matching and exponential power gain of traveling
microwaves to take place over a wide frequency range. We report the
proof-of-principle experiment performed at a temperature of T = 4.2 K on Nb
trilayer samples, which has demonstrated that our concept of a practical
broadband Josephson parametric amplifier is valid and very promising for
achieving quantum-limited operation.
