Tunable Superconducting Qubits with Flux-Independent Coherence

As superconducting-qubit architectures progress to more complex layouts, frequency crowding in qubit arrays increasingly hinders computing performance. Frequency-tunable qubits can assuage this problem, but are subject to the magnetic-flux noise that is ubiquitous in such circuitry. The authors exploit asymmetric Josephson junctions in transmon qubits to reduce sensitivity to flux noise, while preserving sufficient tunability to avoid frequency collisions. In their most asymmetric qubit, dephasing due to flux noise is reduced to the point where its rate is independent of the flux bias.