LAUSR

We design a sub-gigahertz Josephson parametric amplifier for the readout of nanoscale calorimeters which consist of normal-metal–superconductor heterostructures. We characterize the amplifier performance at two operating points, 605 and 655 MHz, corresponding to reproducible local frequency maxima with respect to the applied magnetic flux. At the 655 MHz operating point, the device displays its maximum small-signal gain of 32 dB and gain-bandwidth product of . The gain remains above 20 dB for incident powers up to −119 dBm. The added noise of the amplifier, determined by the hot/cold source method, assumes a minimum value of 0.2 K.