Intermodulation measurements in Nb superconducting microstrip resonators

Abstract

The issue of intermodulation distortion in superconducting devices for rf and microwave applications is discussed. The classical frequency conversion theory for nonlinear two-port devices in the small signal limit is shown to apply to microstrip resonators regardless of their geometry and material. Two tone, third order intermodulation measurements allow more sensitive detection of nonlinearity compared to surface impedance measurements, provided a low noise, spurious free experimental setup is adopted. Measurements carried out on high quality Nb meanderline microstrip resonators show that at very low power level nonlinearity is dominated by intrinsic device properties. Film defects start to play a predominant role above a critical power level that strongly depends on the defect’s nature.

Readout-power heating and hysteretic switching between thermal quasiparticle states in kinetic inductance detectors

“…Intermodulation measurements can indicate which mechanism causes nonlinearities. 14,19 In most mechanisms, the superconductor film quality plays a crucial role in the power handling. 6 Quasiparticle heating is sometimes mentioned but neglected due to the relatively high thermal conductivity of high-T c superconductors.…”

Linear and nonlinear electrodynamic responses of bulk CaC6 in the microwave regime

“…In the extremely low power region -where the surface resistance of CaC 6 shows no detectable dependence on the microwave field at all -the IMD response follows the expected cubic dependence on P circ [15]. According to the theory first set by Dahm and Scalapino [16], the non linear response of a superconductor measured by P IMD (the output power due to the third order IMD) can be used as a very sensitive probe of the superconducting gap function symmetry, by means of the nonlinear parameter b(T).…”

Intermodulation gain in nonlinear NbN superconducting microwave resonators

“…In the present work, we examine these nonlinear resonators from another aspect by applying intermodulation measurements, which are considered one of the effective tools for detecting and studying nonlinearities in microwave superconducting devices. [4][5][6][7][8][9][10][11][12] The results of the intermodulation measurements of these resonators not only provide an important insight as to the possible nonlinear mechanisms responsible for the observed dynamics, 5,11 they exhibit interesting unique features as well. We show that driving the nonlinear resonator to its onset of instability while injecting two closely spaced unequal tones lying within the resonance band into the resonator results in high amplification of both the low-amplitude injected signal and the idler ͑the tone generated via the nonlinear frequency mixing of the resonator͒.…”