Tunable Superconducting Flux Qubits with Long Coherence Times
Tikai Chang, Tamar Cohen, Itamar Holzman, Gianluigi Catelani, Michael Stern
Abstract
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 $\ifmmode\pm\else\textpm\fi{}3.5\phantom{\rule{0.2em}{0ex}}\mathrm{GHz}$ around their central gap frequency. The measured relaxation times are limited by dielectric losses in the substrate and can attain ${T}_{1}\ensuremath{\sim}8\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{s}$. The echo dephasing times are limited by flux noise even at optimal points and reach ${T}_{2E}\ensuremath{\sim}4\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{s}$, almost an order of magnitude longer than state of the art.