Gain, noise and intermodulation in a nonlinear superconducting resonator
Intermodulation Products AB, Solna, Sweden
10 Nanostructure Physics, Royal Institute of Technology (KTH), Stockholm, Sweden
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Accepted: 6 January 2014
Published online: 7 March 2014
A superconducting microwave resonator is modified with several weak links to make it nonlinear and operated as a phase-insensitive microwave amplifier. Signal gain is demonstrated by intermodulation with a strong pump. The gain is sharply frequency dependent, and we demonstrate phase dependence by examining correlations between the signal and one idler which is a 3rd order intermodulation product of the pump and signal tones. A calibration procedure is described which is based on measurement of both thermal and quantum noise, revealing that the following HEMT amplifier adds noise at 15 times the quantum limit. When operated as a phase-insensitive amplifier the nonlinear resonator added noise at 2.5 times the quantum limit. Significant power is found at intermodulation products beyond 3rd order, which may be responsible for the inability to reach the quantum limit.
PACS Codes: 74.78.-w, 42.65.Yj, 85.25.Cp.
Key words: intermodulation / parametric amplifier / quantum noise
© The Author(s), 2014