Fault-Tolerant Logical Gates in the IBM Quantum Experience
Quantum computers will require encoding of quantum information to protect
them from noise. Fault-tolerant quantum computing architectures illustrate how
this might be done but have not yet shown a conclusive practical advantage.
Here we demonstrate that a small but useful error detecting code improves the
fidelity of the fault-tolerant gates implemented in the code space as compared
to the fidelity of physically equivalent gates implemented on physical qubits.
By running a randomized benchmarking protocol in the logical code space of the
[4,2,2] code, we observe an order of magnitude improvement in the infidelity of
the gates, with the two-qubit infidelity dropping from 5.8(2)% to 0.60(3)%. Our
results are consistent with fault-tolerance theory and conclusively demonstrate
the benefit of carrying out computation in a code space that can detect errors.
Although the fault-tolerant gates offer an impressive improvement in fidelity,
the computation as a whole is not below the fault-tolerance threshold because
of noise associated with state preparation and measurement on this device.
Robin Harper Steven T. Flammia