Microsoft & Quantinuum: 4 Logical Qubits with 800× Error Improvement

Microsoft’s qubit-virtualization system on Quantinuum’s H2 hardware created 4 highly reliable logical qubits from 30 qubits — delivering an 800× improvement in logical error rate (circuit error rate 10⁻⁵) over physical qubits, with 14,000 error-free independent runs.

In April 2024, Microsoft and Quantinuum achieved a landmark in fault-tolerant quantum computing: 4 highly reliable logical qubits (LQ) created from just 30 of the 32 available qubits on Quantinuum’s H2 trapped-ion system — a 7.5:1 resource-to-logical overhead ratio.

The key result was an 800× improvement in logical error rate. The entangled logical qubits exhibited a circuit error rate of 10⁻⁵ (one error per 100,000 runs), versus the base qubit circuit error rate of 8×10⁻³. Across 14,000 independent runs, not a single logical error was detected. Active syndrome extraction — diagnosing and correcting errors without destroying the logical qubits — was also successfully demonstrated, satisfying all three fundamental criteria for reliable quantum computing: entangling ≥2 logical qubits, correcting all individual circuit errors, and achieving a large resource-to-logical error rate separation.

This result, achieved by coupling Microsoft’s qubit-virtualization system with Quantinuum’s H-Series ion-trap hardware (99.8% two-qubit gate fidelity), establishes 4 LQ as the industry benchmark for reliability at that time and marks the transition to reliable quantum computing — a prerequisite for a hybrid classical-quantum supercomputer.