Experimental error suppression in Cross-Resonance gates via
  multi-derivative pulse shaping
While quantum circuits are reaching impressive widths in the hundreds of
qubits, their depths have not been able to keep pace. In particular, cloud
computing gates on multi-qubit, fixed-frequency superconducting chips continue
to hover around the 1% error range, contrasting with the progress seen on
carefully designed two-qubit chips, where error rates have been pushed towards
0.1%. Despite the strong impetus and a plethora of research, experimental
demonstration of error suppression on these multi-qubit devices remains
challenging, primarily due to the wide distribution of qubit parameters and the
demanding calibration process required for advanced control methods. Here, we
achieve this goal, using a simple control method based on multi-derivative,
multi-constraint pulse shaping, which acts simultaneously against multiple
error sources. Our approach establishes a two to fourfold improvement on the
default calibration scheme, demonstrated on four qubits on the IBM Quantum
Platform with limited and intermittent access, enabling these large-scale
fixed-frequency systems to fully take advantage of their superior coherence
times. The achieved CNOT fidelities of 99.7(1)% on those publically available
qubits come from both coherent control error suppression and accelerated gate
time.
Boxi Li Tommaso Calarco Felix Motzoi