Leakage dynamics and reduction in disordered transmon arrays and tunable couplers

Transmon superconducting qubits face errors from leakage when control flaws populate energy levels above the computational states. Using numerical simulations, this thesis investigates leakage reduction units engineered to clear these extra excitations without perturbing qubit states. One studied configuration transfers leakage along a transmon chain into an external sink, reliably removing the excess energy while protecting the qubit. The research also shows that repeated measurements across transmon chains trigger an entanglement phase transition. Furthermore, the study analyzes leakage in architectures with tunable couplers, finding that leakage moves between qubits even when interactions are shut off. Leveraging these dynamics enables tunable-coupler units that extract leakage more quickly and with fewer disturbances to the qubit than transmon-chain devices.