Flux-insensitive qubit from a split transmon shunted with a Josephson junction

Xiao Geng; Linpan Jiang; Mingjun Cheng; Jianshe Liu; Wei Chen

doi:10.1103/PhysRevA.110.062607

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Flux-insensitive qubit from a split transmon shunted with a Josephson junction

Xiao Geng, Linpan Jiang, Mingjun Cheng, Jianshe Liu, Wei Chen

DOI 10.1103/PhysRevA.110.062607 · Physical Review A

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Abstract

Split transmons have been widely used in making quantum processors for building scalable and fault-tolerant superconducting quantum computers. With tunable external flux threading the superconducting quantum interference devices (SQUIDs) of qubits, split transmons have a degree of freedom for tuning frequencies but introduce flux noise as an important dephasing factor at the same time. Here, an improved version of a transmon is proposed and is called a “triple-Josephson-junction transmon” (tri-JJ transmon). A tri-JJ transmon is obtained by shunting another Josephson junction to the SQUID of a split transmon, which can produce much more different local minima and maxima of qubit frequencies tuned by external flux as “sweet spots” than those of split transmons. The first-order effect of the flux noise at the sweet spots can be eliminated and the corresponding pure-dephasing times are estimated as about 200µs by considering only critical current noise. Tri-JJ transmons are compatible with the process and the protocol of control and measurement of split transmons and can be competitive candidates for constructing a high-performance superconducting quantum processor.