Fault-Tolerant Logical Gates in the IBM Quantum Experience

TL;DR

This paper demonstrates that using a small error-detecting code in a quantum computer significantly improves the fidelity of logical gates, providing experimental evidence for the benefits of fault-tolerant quantum computing.

Contribution

The study provides the first experimental demonstration of improved logical gate fidelity using a fault-tolerant code in the IBM Quantum Experience.

Findings

Order of magnitude reduction in two-qubit gate infidelity

Logical gate fidelity surpasses physical gate fidelity in the code space

Results align with fault-tolerance theory expectations

Abstract

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.