Reproducibility and Gap Control of Superconducting Flux Qubits

Abstract

Superconducting flux qubits are promising candidates for the physical realization of a scalable quantum processor. Indeed, these circuits may have both a small decoherence rate and a large anharmonicity. These properties enable the application of fast quantum gates with high fidelity and reduce scaling limitations due to frequency crowding. The major difficulty of flux qubits' design consists of controlling precisely their transition energy---the so-called qubit gap---while keeping long and reproducible relaxation times. Solving this problem is challenging and requires extremely good control of e-beam lithography, oxidation parameters of the junctions, and sample surface. Here we present measurements of a large batch of flux qubits and demonstrate a high level of reproducibility and control of qubit gaps ($\ifmmode\pm\else\textpm\fi{}0.6\phantom{\rule{0.2em}{0ex}}\mathrm{GHz}$), relaxation times ($15$--$20\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{s}$), and pure echo dephasing times ($15$--$30\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{s}$). These results open the way for potential applications in the fields of quantum hybrid circuits and quantum computation.