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3D Circuit Quantum Electrodynamincs with Flux Qubits

Final Report Summary - CQ3D (3D Circuit Quantum Electrodynamincs with Flux Qubits)

CIG program cQ3D was designed to facilitate the integration of tenure-tracker PI DiCarlo and his young research team into the Kavli Institute of Nanoscience at Delft University of Technology (TUD). The program has developed along two main fronts: (1) infrastructure (simulation software and fabrication materials/equipment) enabling robust design and processing of superconducting qubits and resonators in the circuit quantum electrodynamics (cQED) architecture for quantum computing; and (2) a research agenda stimulating collaboration with local faculty members.
The infrastructure developments have produced the following most notable results:
- Fabrication of aluminum-based transmon qubits coupled to 3D resonators with state of the art coherence, allowing detailed study and identification of dominant energy relaxation mechanisms in these qubits, including quasiparticle-tunneling effects.
- Strong coupling of coherent electron-spin ensembles of P1 centers in diamond to magnetic-field compatible resonators.
- Through simulation-inspired fabrication, an improvement in the performance of qubits and resonators in 2D cQED by incorporating 3D features, such as deeply-etched substrates and large capacitive gaps. These have significantly narrowed the performance gap between 2D and 3D approaches to cQED.
- Realization of flux qubits made from superconductor-normal-superconductor junctions with magnetic-field compatible materials.

This program has produced 4 publications most closely related to the program scientific agenda. The infrastructure developments have influenced all activities in the group, for a total of 12 published experimental papers by the group during this integration period. Most importantly, the program has fostered collaborations with many faculty members at the host institution, including experimentalists R. Hanson, L. Kouwenhoven, L. Vandersypen, and E. Bakkers, as well as theorists A. Akhmerov and Ya. Blanter. These collaborations have contributed to the successful integration of DiCarlo lab into both the Kavli Institute and the newly-formed QuTech Institute also at TUD, and contributed to the promotion of PI DiCarlo to a tenured, associate professorship in October 2015.