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. 2020 Mar 20;6(12):eaay3050. doi: 10.1126/sciadv.aay3050

Fig. 4. Protecting entanglement from general qubit error and leakage.

Fig. 4

(A) Simplified quantum circuit with preparation, repeated pairs of ZZ and XX checks, and data-qubit tomography. (B) Fidelity to ∣Φ+⟩ as a function of M, extracted from the data-qubit tomography. “No error” postselects the runs in which no error is detected (postselected fraction in fig. S5). “Final” applies PFU based on the last three outcomes (equivalent to MWPM). “Final + HMM” includes mitigation of leakage. “First” uses only the first pair of parity outcomes. (C and D) Corresponding 〈X ⊗ X〉 and 〈Z ⊗ Z〉. Curves in (B) to (D) are best fits of a simple exponential decay.