This figure demonstrates the parametric interaction of the open-circuited SQUID at the signal and idler frequencies. As opposed to Section 7.1, these series bandpass filters are now zero impedance at bandpass and blocking at all other frequencies. This works in such a way that frequencies other than and now present an open circuit to the pumped SQUID. Therefore the voltage across the SQUID is not necessarily zero at these other frequencies. These additional mixing effects can be mapped onto a modified subsystem between signal and idler, which is the matrix of Eq. (71).