Accurate Leakage Speculation for Quantum Error Correction

TL;DR

The paper introduces gladiator, a framework that accurately detects leakage in quantum error correction, reducing unnecessary interventions, shortening cycles, and improving overall fault-tolerance in quantum computing.

Contribution

Gladiator provides a code-aware, adaptable leakage speculation method that significantly reduces false positives and enhances efficiency across various quantum error correction codes.

Findings

Up to 3x reduction in unnecessary leakage-reduction circuits

Shortened quantum error correction cycles by 2x on average

Achieved 16% lower logical error rate in benchmarks

Abstract

Quantum Error Correction (QEC) protects qubits against bit- and phase-flip errors in the |0> or |1> subspace, but physical qubits can also leak into higher energy levels (e.g., |2>). Leakage is especially harmful, as it corrupts all subsequent syndrome measurements and can spread to neighboring qubits. Detecting leakage on data qubits is particularly challenging, since they are never measured directly during QEC cycles. Prior work, such as eraser, addresses this by inferring leakage from syndrome patterns using a fixed heuristic. However, this approach often misclassifies benign syndromes, triggering excessive leakage-reduction circuits (LRCs). Because LRCs are themselves noisy and slow, these false triggers lengthen QEC cycles and inflate logical error rates. We propose gladiator, a general and adaptable leakage speculation framework that works across surface code, color code, and qLDPC codes. Offline, gladiator builds a code-aware error-propagation graph calibrated to device data. Online, it classifies each syndrome in a few nanoseconds and schedules LRC only when the observed pattern is provably leakage-dominated. This precise speculation eliminates up to 3x (and on average 2x) unnecessary LRCs, shortens QEC cycles, and suppresses false positives at their source. Evaluated on standard fault-tolerant benchmarks, gladiator delivers 1.7x-3.9x speedups and 16% reduction in logical error rate, advancing the efficiency of fault-tolerant quantum computing.