The Flux Qubit Revisited to Enhance Coherence and Reproducibility

Understand

The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits).

• Here, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of $40\,\mu$s at its flux-insensitive point.
• Qubit relaxation times $T_1$ across 22 qubits are consistently matched with a single model involving resonator loss, ohmic charge noise, and 1/f flux noise, a noise source previously considered primarily in the context of dephasing.
• We furthermore demonstrate that qubit dephasing at the flux-insensitive point is dominated by residual thermal photons in the readout resonator.