Fast Tunable Coupler Architecture for Fixed Frequency Transmons

The limits of fixed coupling architectures for superconducting quantum computation have long been recognized. This has led to the development of various tunable coupling schemes [1,2]. In this talk we will explore a tunable capacitive coupler, which interferes a direct coupling capacitance with coupling through a tunable qubit. Unlike previous proposals [2], we place the direct capacitance between opposite islands of the transmons compared to the coupling qubit. This arrangement allows us to operate with the coupler frequency below the qubits and thus in a regime with reduced noise susceptibility and a better on/off ratio compared to previously published designs [2]. With this coupler we demonstrate operation of cPhase gates in low detuning regimes and further demonstrate a two qubit CZ gate with 99.8% fidelity.
[1] Chen Yu et al. Phys. Rev. Lett. 113, 220502 (2014)
[2] F. Yan et al. Phys. Rev. Applied. 10, 054063 (2018)