Extended Data Fig. 3: Loss in visibility when initializing all qubits.

a, Gate sequence used to demonstrate the effect of running different qubit initialization routines. Microwave bursts with variable duration are performed sequentially on qubits Q2, Q3, Q4 and Q5, as shown in the schematic. In all cases, readout is performed on all the qubits, but we vary which qubits are initialized for a particular experiment. b–d, Results of the sequence displayed in panel a, when qubit Q1-Q3 (b), Q4-Q6 (c) or Q1-Q6 (d) are initialized. The shaded numbers in the panels indicate the visibility of the measured qubit. With all qubits initialized we observe a visibility loss on qubit Q4 and to a lesser extent qubit Q3. A visibility loss in principle can originate from a reduced readout or initialization fidelity. We keep the readout sequence identical for a, b, and c. Additionally, we include a 500 μs waiting time prior to readout, to minimize any effects of MW pulsing during initialization or manipulation stage on the readout performance (see Methods). Although, we cannot be certain that the readout fidelity is unaffected by the initialization of all qubits, we speculate that the majority of the observed visibility loss is due to a reduced initialization fidelity, possibly due to the sensitivity of the CROTs to qubit frequency shifts. This interpretation is consistent with the fact that mostly qubit Q4 suffers a lower visibility, as qubit Q4 is initialized before qubits Q1, Q2 and Q3. If instead we reverse the initialization order, qubit Q3 displays lowered visibility (data not shown).