Bounds on cross-resonance gate fidelity in an extended parameter regime

The cross-resonance (CR) interaction is the primary method for enabling two-qubit gates in systems with fixed-frequency transmons using only microwave control. Eliminating the need for tunable circuit elements reduces the system's susceptibility to low-frequency noise, but the cost is more complicated coherent dynamics during the gate [1,2,3,4], both between the targeted qubit pair and to qubits that are nominally idle (spectators). We bound the two-qubit CR gate fidelity as set by unitary dynamics, showing its sensitivity to the parameters governing the two-qubit interaction (coupling strength, relative energies, anharmonicities, and total gate time) and to parameters required to build larger devices (frequency allocation of neighboring qubits). As we reach the limit of fidelities achieved by control of our current devices, consideration of this larger parameter space will let us design devices with higher performance.

[1] Magesan, Gambetta, arXiv:1804.04073 (2018)
[2] Sheldon, Magesan, Chow, Gambetta, Phys. Rev. A 93, 060302 (2016)
[3] Tripathi, Khezri, Korotkov, Phys. Rev. A 100, 012301 (2019)
[4] Kirchhoff, Keßler, Liebermann, Assémat, Machnes, Motzoi, Wilhelm, Phys. Rev. A 97, 042348 (2018)