Flux Qubits Fabricated using a High-Coherence Transmon Fabrication Process*

The coherence of superconducting circuit qubits has dramatically improved since initial implementations, leaping from T₁ ~1 ns in early Cooper pair boxes to now attaining ~100 μs in transmons. Much of this improvement has involved careful electromagnetic design paired with fabrication and material research. Our in-house fabrication protocol has been previously optimized for transmons, and we now apply these methods to flux qubits. Numerical simulations were performed to investigate the flux qubit energy spectrum, qubit-resonator coupling, and noise susceptibility to inform design parameters. After optimizing the fabrication process, we present work investigating flux qubits in 3D cavities, in addition to an 8-qubit ring of alternating flux qubits and transmons with nearest neighbor coupling. We perform initial investigations into two-qubit gates between flux qubits and transmons of opposing anharmonicity.