Extended Data Fig. 9: Multiplexed entanglement: sequence detail and parity measurements.

a, After parallelized initialization of all four ions, two consecutive entanglement attempts are performed, first on Pair 2 (consisting of Ions 3 and 4), then on Pair 1 (consisting of Ions 1 and 2), as depicted in the pulse sequences. We note that all four ions have frequency-resolved optical transitions enabling independent optical control. However, due to the narrow distribution of qubit transition frequencies, all microwave control pulses are globally applied to ions in the same device. If either entanglement attempt is successful, the sequence proceeds to apply dynamic rephasing and phase compensation protocols exclusively to the corresponding ion pair. Details of these pulse sequences can be found in Extended Data Fig. 4. Finally, we measure two-qubit populations of the entangled pair in the XX, YY or ZZ bases. b, We segregate our multiplexed experimental results into two separate data sets corresponding to successful heralding attempts for Pair 1 and Pair 2. For each data set we plot population histograms in the XX, YY and ZZ bases for a photon acceptance window size of 500 ns with corresponding fidelities of \({{\mathcal{F}}}_{{\rm{m}}{\rm{u}}{\rm{l}}{\rm{t}}}^{(1)}=0.700\,\pm \,0.005\) and \({{\mathcal{F}}}_{{\rm{m}}{\rm{u}}{\rm{l}}{\rm{t}}}^{(2)}=0.668\,\pm \,0.006\) for Pair 1 and Pair 2, respectively.