  We report the implementation of a near-quantum-limited, traveling-wave
parametric amplifier that uses three-wave mixing (3WM). To favor amplification
by 3WM, we use the superconducting nonlinear asymmetric inductive element
(SNAIL) loops, biased with a dc magnetic flux. In addition, we equip the device
with dispersion engineering features to create a stop-band at the second
harmonic of the pump and suppress the propagation of the higher harmonics that
otherwise degrade the amplification. With a chain of 440 SNAILs, the amplifier
provides up to 20 dB gain and a 3-dB bandwidth of 1 GHz. The added noise by the
amplifier is found to be less than one photon.
