  For a frequency-tunable two-qubit system, a controlled-Z (CZ) gate can be
realized by adiabatically driving the qubit system through an avoided level
crossing between an auxiliary state and computational levels. Here, we
theoretically propose a fast CZ gate using a shortcut-to-adiabaticity (STA).
Experimentally, the STA CZ gate is implemented with a 52 ns control pulse for
two coupled superconducting Xmon qubits. Measured fidelity of the STA CZ gate
is higher than 96.0%, in both quantum process tomography and randomized
benchmarking. The protocol allows a flexible design of the evolution time and
control waveform. We suggest that this `fast adiabatic' CZ gate can be directly
applied to other multi-qubit quantum systems.
