  Quantum computers built with superconducting artificial atoms already stretch
the limits of their classical counterparts. While the lowest energy states of
these artificial atoms serve as the qubit basis, the higher levels are
responsible for both a host of attractive gate schemes as well as generating
undesired interactions. In particular, when coupling these atoms to generate
entanglement, the higher levels cause shifts in the computational levels that
leads to unwanted $ZZ$ quantum crosstalk. Here, we present a novel technique to
manipulate the energy levels and mitigate this crosstalk via a simultaneous AC
Stark effect on coupled qubits. This breaks a fundamental deadlock between
qubit-qubit coupling and crosstalk, leading to a 90ns CNOT with a gate error of
(0.19 $\pm$ 0.02) $\%$ and the demonstration of a novel CZ gate with
fixed-coupling single-junction transmon qubits. Furthermore, we show a
definitive improvement in circuit performance with crosstalk cancellation over
seven qubits, demonstrating the scalability of the technique. This work paves
the way for superconducting hardware with faster gates and greatly improved
multi-qubit circuit fidelities.

Quantum Physics