ºÚÁÏÍø

Title of the thesis: State-of-the-Art Core Operations in Superconducting Quantum Processors

Thesis defender: Fabian Marxer
Opponent: Associate Professor Morten Kjaergaard, Niels Bohr Institute, University of Copenhagen, Denmark
Custos: Prof. Mikko Möttönen, Aalto University School of Science

Quantum error correction places strict demands on the underlying hardware: the core operations of a quantum processor, including single qubit gates, two qubit entangling gates, readout, and reset, must reach very low error rates while remaining stable and scalable. This thesis investigates how far superconducting circuits based on transmon qubits can be pushed toward these limits, and how device architecture and control choices can be co designed to reduce the overhead required for fault tolerant quantum computation.

A main focus is high fidelity control using tunable coupler architectures that enable fast controlled Z gates while maintaining good single qubit performance. The thesis develops and characterizes coupler based designs, including long distance coupling that relaxes layout constraints, and shows how optimizing couplings can support strong performance for both single and two qubit gates on the same chip. It also introduces calibration and benchmarking tools that improve the accuracy of diabatic controlled Z tuning, including a protocol that makes small over and under rotations easier to detect and correct, and combines these advances with modern pulse shaping methods and high fidelity measurement techniques.

Beyond gates and readout, the thesis also explores additional building blocks for scalable superconducting systems. It studies fast unconditional qubit reset using engineered dissipation, and demonstrates remote state transfer and entanglement between two dilution refrigerators through a cryogenic microwave link, pointing toward modular and distributed architectures. Together, these results show that careful co design across layout, coupling topology, pulse shaping, calibration, readout, and reset can bring a coherent hardware and control stack closer to the requirements of large scale quantum computing.

Keywords: Superconducting quantum circuits, Transmon qubits, Tunable couplers, Two-qubit gates (CZ), High-fidelity quantum control

Contact information:  

Thesis available for public display 7 days prior to the defence at .