Quantum computing has been envisioned to offer unprecedented advantages over conventional supercomputers in certain computational applications such as drug discovery and materials design. Despite of the tremendous developments in recent years, concerns about building a practical quantum computer persist. This Letter examines, from engineering viewpoint, the grand challenges to building such a machine based on the leading technology platform “transmon”. The examination leads to proposal of technological solutions to break the scalability barriers that originate from the physics behind the transmon design, thereby to enable giga-scale integration necessary for the promised applications.
Superconducting transmon qubits have seen significant progress in the last five years. By optimizing and exploring different fabrication process and superconducting material, transmon lifetime is more than 100 us with single-qubit gate and two-qubit gate fidelity is higher than to 99.8%. This thesis reports work to realize a transmon qubit fabrication process and experiment test bed. The experiment stage at the mixing chamber of the dilution fridge is designed and the microwave setup for qubit control and characterization is demonstrated. The qubit fabrication recipe using aluminum and Al/AlOx/Al junction is developed and measured. The qubit lifetime reach an average of 10 us and single-qubit gate fidelity is F = 99.883 +- 0.007%. While the parameters are moderate compared to the state of the art, this system is a good stepping stone to explore qubit scaling and optimization.