Chaotic and stochastic phenomena in superconducting quantum interferometers

Complex chaotic and stochastic phenomena in single-junction and double-junction superconducting quantum interferometers are studied with the help of specially designed high-speed analog circuit. In contrast with the earlier versions of the Josephson junction analogs, the digital integrated circuits with the voltage-controlled time delay have been used as the basic elements of the circuit, which has enabled us to extend its frequency range up to 100 KHz. Of the phenomena studied with the analog, two are discussed in detail: i. For the single-junction interferometer under the periodic external drive the region of parameters is found, where the device exhibits complex and chaotic behavior and thus cannot be used in parametric amplifiers and ac SQUIDs. The boundary of the chaotic behavior region’ is found to be very close to that predicted from a very simple criterion. ii. For the double-junction interferometer, we have measured the probability of the establishing the basic (“O-th”) static state as a result of a slow decrease of the bias current, as a function of the interferometer parameters. The region is determined where the probability is very close to unity, and the interferometer can be used as an NDRO memory cell.