Improving the frequency reproducibility of transmon qubits to lower the crosstalk in quantum processors*

This work targets frequency crowding in superconducting quantum computing devices that is a profound challenge towards scalability of architectures with fixed-frequency qubits. Fixed-frequency qubits show superior performance in terms of coherence compared to tunable qubits. However, they suffer from deviations in their frequency from the designed value, due to imperfections in the fabrication process of Josephson junctions that cause variation in junctions' normal state resistance. This leads to crosstalk between neighboring qubits and to scale beyond hundreds of qubits, a significant reduction in the frequency variation is required. We discuss and demonstrate possible means of improving the spread in Josephson junction resistance, to values close to the required limit for scalability.