Ph.D Thesis

Ph.D StudentSegev Eran
SubjectMetastability and Self-Oscillations in Superconducting
Microwave Resonators Integrated with
a dc-SQUID
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Eyal Buks
Full Thesis textFull thesis text - English Version


    Nonlinear effects in superconductors have significant implications for both basic science and technology. Strong nonlinearity may be exploited to study some important quantum phenomena in the microwave region, such as quantum squeezing, circuit cavity quantum electrodynamics in the strong and the dispersive coupling regimes, and experimental observation of the so called dynamical Casimir effect. These effects also allow some intriguing technological applications such as Josephson bifurcation amplifiers for quantum-limited measurements, tunable resonators, and single photon detectors.

    We first theoretically and experimentally study thermal instability in superconducting stripline resonators working at gigahertz frequencies. We demonstrate how at a certain range of driving parameters, thermal instability creates extremely strong nonlinearity, which is manifested by self-sustained oscillations of the resonators at megahertz frequencies. This phenomenon is of a significant importance as it introduces an extreme nonlinearity, which is by far stronger than any other nonlinearity observed before in superconducting resonators. It results in a very high intermodulation gain, substantial noise squeezing, stochastic resonance, sensitive radiation detection, and strong coupling between different resonance modes. The source for the strong amplification along the thresholds of the self-oscillations is investigated and found to be a unique stochastic resonance between stable and unstable states of the resonator.

    We further study metastable response of hysteretic nano-bridge based DC Superconducting QUantum Interference Devices (SQUIDs), subjected to an alternating biasing current, both theoretically and experimentally. SQUIDs based on nano-bridges constitute an emerging technology with a potential to out-perform traditional SQUIDs, based on superconducting-insulating-superconducting junctions, in terms of noise performance. We theoretically analyze stability zones of a highly hysteretic DC-SQUID in the plane of the bias current and magnetic flux control parameters, and find a periodic dissipative stability zone, which differs from the well known oscillatory zone that is found above the critical current of the SQUID. When such a SQUID is integrated in a resonator we find that thermal processes, which have similar characteristic rate as the resonance frequencies of the resonator, play an important role in the overall measured dynamics of the device. In addition, we find that self-oscillations, which emerge in the integrated resonator-SQUID device, periodically depend on the external magnetic flux.