THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Towards Superconducting Monolithic Microwave Integrated Circuits

The superconducting Monolithic Microwave Integrated Circuit (MMIC) is vital in all modern superconducting Rapid Single Flux Quantum (RSFQ) digital systems. Importance of microwave components comes from the fact that superconducting circuits operate with an ultra-wide band signal in the ultra-low dissipation environment. At a typical signal bandwidth of 300 GHz, even a 100μm superconducting wire becomes a passive transmission line forming resonator with quality factor more than 1000. Therefore new design problems should be solved for the implementation of large scale superconducting circuits. This thesis covers different levels of the microwave circuit/MMIC design for superconducting digital circuits: EM simulations of interconnects, analog simulations of the single RSFQ logic cells, design and optimization of microwave structures. The main outcomes of the thesis are practical designs of the interconnect that allow implementation of the System-in-Package for a superconducting Digital Signal Processor capable of performing 30Giga operations per second. General scaling rules for interconnect bandwidth vs. current density of the fabrication processes have been derived. Significant part of the thesis is dedicated for a MMIC used in classical interface for superconducting qubits. A scalable RSFQ input-interface for qubit minimizes power dissipation, noise and most importantly the cost. Furthermore, it provides architecture for multi-qubit systems with minimum complexity. The multi-qubit architecture requires frequency selections and thus needs highly selective filters (ultra-narrowband). Ultra narrowband is also required for desired small linewidth of the signal in order to minimize noise. The primary focus of this work is on the development of superconducting microwave components as input-interfaces between RSFQ and superconducting qubits. However, this implementation requires careful design and miniaturization of both passive and tunable microwave structures. The RSFQ input-interface for qubits consists of the two main blocks: RSFQ control of a microwave I-Q pulse generator and RSFQ control for frequency selection. An allsuperconducting microwave I-Q pulse generator is based on SQUID chains as tunable microwave components. The SQUID chain acts as a tunable inductance in microwave resonators. Tuning via magnetic field enables variable frequency response for these microwave components. The magnetic field is supplied by the RSFQ interface blocks. Design of all passive components has been done using a unique method developed to allow drastic reduction the components’ size. As a result the passive components with dimensions less than 4% of the wavelength can be integrated on-chip with digital circuits. Several components of the RSFQ input-interface for quantum computing have been developed. A 2GHz lumped filter, 5 GHz quasi-lumped filter, SQUID based 1.83.5GHz tunable filter, 3.5-5GHz tunable phase shifter, 3.16GHz microwave modulator, RSFQ driver circuits and microwave interconnects have been designed and experimentally verified.