Experimental Characterization of Fault-Tolerant Circuits in Small-Scale Quantum Processors

Understand

Experiments conducted on open-access cloud-based IBM Quantum devices are presented for characterizing their fault tolerance using $[4,2,2]$-encoded gate sequences.

• Up to 100 logical gates are activated in the IBMQ Bogota and IBMQ Santiago devices and we found that a $[4,2,2]$ code's logical gate set may be deemed fault-tolerant for gate sequences larger than 10 gates.
• However, certain circuits did not satisfy the fault tolerance criterion.
• In some cases, the encoded-gate sequences show a high error rate that is lower bounded at $\approx 0.1$, whereby the error inherent in these circuits cannot be mitigated by classical post-selection.