Fig. 4
QPT of the geometric three-qubit CCZ gate, obtained with the drive amplitude \(\Omega {\rm{/}}2\pi \approx \sqrt {7.5}\) MHz and detuning δ/2π = 4 MHz. The color code for Pauli basis {I, X, Y, Z} is shown at the top-left corner. The process matrix is reconstructed by preparing a complete set of 64 input states, and measuring both the input and output density matrices using QST. The ideal (χ id) and experimental (χ exp) quantum process matrices are presented in the left and right panels, respectively. Imaginary components of χ exp are measured to be no larger than 0.063 in magnitude. The fidelity of χ exp is 0.868 ± 0.004. The \(\left| 2 \right\rangle\)-state occupation probability of each qubit resulting from the drive Ω is no higher than 0.025 in a separate measurement, in which the test qubit is initialized in \(\left| 1 \right\rangle\) and the other two qubits are in \(\left| 0 \right\rangle\)
