  Experimental investigations of the nonlinear properties of superconducting
niobium coplanar waveguide resonators are reported. The nonlinearity due to a
current dependent kinetic inductance of the center conductor is strong enough
to realize bifurcation of the nonlinear oscillator. When driven with two
frequencies near the threshold for bifurcation, parametric amplification with a
gain of +22.4 dB is observed.
