Parametric amplification in arrays of Josephson tunnel junctions

Arrays of 30 series-connected unbiased small Josephson tunnel junctions give parametric amplification at 10 GHz. A pump power of 10-8 W was required and gains of up to 24 dB were achieved. The gain was constant for a large range of signal power, up to a signal output power of 10 dB below the pump power. A maximum brightness temperature of 1.7 x 106 K, in a bandwidth of 12 MHz, was deduced from variations of the gain with input noise level