Fig. 5: Experimental results of MEADD for characterizing crosstalk.
From: Characterizing coherent errors using matrix-element amplification
a Evolution of the components of the Bloch vector in the odd-parity sector, \({X}_{{\rm{odd}}}=\left\vert 10\right\rangle \left\langle 01\right\vert +\left\vert 01\right\rangle \left\langle 10\right\vert\), \({Y}_{{\rm{odd}}}=i\left\vert 10\right\rangle \left\langle 01\right\vert -i\left\vert 01\right\rangle \left\langle 10\right\vert\), and \({Z}_{{\rm{odd}}}=\left\vert 01\right\rangle \left\langle 01\right\vert -\left\vert 10\right\rangle \left\langle 10\right\vert\), for two neighboring qubits involved in 2n parallel CZ gates. The corresponding crosstalk angle is about 4 mrad per cycle. Error bars correspond to the standard deviation over 2000 shots and are smaller than the data markers. Distributions of b the median crosstalk swap angle θxtalk and c the run-to-run standard deviation in this estimate after repeating the measurement 10 times over 1 h for 24 neighboring CZ gates on the Sycamore processor, revealing a median signal 6 times larger than the median noise. As shown in the inset, the 34 ns CZ gates (gray) are performed simultaneously on neighboring qubit pairs (green and yellow), and we use MEADD to characterize the residual swap angle produced by these operations, yielding θxtalk = (0.42 ± 0.07) mrad on median.
