Tunable Superconducting Flux Qubits with Long Coherence Times

In this work, we study a series of tunable flux qubits inductively coupled to a coplanar waveguide resonator fabricated on a sapphire substrate. Each qubit includes an asymmetric superconducting quantum interference device, which is controlled by the application of an external magnetic field and acts as a tunable Josephson junction. The tunability of the qubits is typically +/- 3.5 GHz around their central gap frequency. The measured relaxation times are limited by dielectric losses in the substrate and can attain T1 similar to 8 mu s. The echo dephasing times are limited by flux noise even at optimal points and reach T2E similar to 4 mu s, almost an order of magnitude longer than state of the art.

Automated summary

In this study, a series of tunable flux qubits coupled to a coplanar waveguide resonator on a sapphire substrate were investigated. Each qubit consists of an asymmetric superconducting quantum interference device that acts as a tunable Josephson junction controlled by an external magnetic field. The tunability of the qubits is typically +/- 3.5 GHz around their central gap frequency. The relaxation times are limited by dielectric losses in the substrate and can reach T1 of approximately 8 μs. The echo dephasing times are limited by flux noise even at optimal points and reach T2E of approximately 4 μs, almost an order of magnitude longer than the state of the art.