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Figure 4 | EPJ Quantum Technology

Figure 4

From: Negative-resistance models for parametrically flux-pumped superconducting quantum interference devices

Figure 4

Considerations of the external circuit for the three-wave nondegenerate case. (a) This figure depicts the physical, general circuit considered in this section, containing a flux-pumped SQUID. This circuit accounts for an external source current, i s , as well as external ( Y ext ) and local shunt ( Y sh ) admittances. (b) It is possible to represent the general circuit in an equivalent way that separates the external loading effects of the circuit at the “signal” ( ω 1 ) and “idler” ( ω 2 ) frequencies. This is done by introducing hypothetical, ideal bandpass filters at ω 1 and ω 2 . These filters act open-circuited at their respective frequency, but short-circuited for all other frequencies. In this representation, the external admittance, Y ext , is represented at different frequencies by Y 1 and Y 2 . The input admittance ( Y SQ ) is then based on the signal voltage response to current i 1 , which depends upon the idler in a way that may allow for gain.

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