Josephson Parametric Amplifiers: Low Noise at 9GHz
The performance of a thin film, (Nb/PbBi), resistive rf-SQUID as a parametric amplifier was investigated at 9 GHz. It was matched to a 50Ω coaxial cable via a low impedance (ZL) microstrip transformer. This allowed relatively high Josephson currents, .Io, to be used. Stable Josephson oscillations were achieved for βLQ=2eIOZL/hf<l.1-1.8. Best amplifier performance was obtained in the 3 and 4 photon, externally pumped modes. Both these two types gave signal gains more than 10 dB and negligible noise power contributions. A hot/cold measurement at a bath temperature of 1.2K gave Gdsb = 13 dB and Tdsb=3±4K over a bandwidth of 310 MHz for the 4 photon amplifier (dsb = double side band). Internally pumped amplifiers were noisier, e.g., a 4 photon one gave single side band noise of the order of 50 K.
KeywordsPump Power Critical Current Tunnel Junction Noise Temperature Shunt Resistor
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