  High-quality two-qubit gate operations are crucial for scalable quantum
information processing. Often, the gate fidelity is compromised when the system
becomes more integrated. Therefore, a low-error-rate, easy-to-scale two-qubit
gate scheme is highly desirable. Here, we experimentally demonstrate a new
two-qubit gate scheme that exploits fixed-frequency qubits and a tunable
coupler in a superconducting quantum circuit. The scheme requires less control
lines, reduces crosstalk effect, simplifies calibration procedures, yet
produces a controlled-Z gate in 30ns with a high fidelity of 99.5%, derived
from the interleaved randomized benchmarking method. Error analysis shows that
gate errors are mostly coherence limited. Our demonstration paves the way for
large-scale implementation of high-fidelity quantum operations.
