Leakage Mobility in Superconducting Qubits as a Leakage Reduction Unit

TL;DR

This study demonstrates that increasing leakage mobility between superconducting qubits can naturally reduce leakage errors, potentially eliminating the need for dedicated leakage reduction units in quantum error correction.

Contribution

It reveals that leakage mobility can serve as an effective leakage mitigation mechanism, challenging the necessity of specialized leakage reduction units in superconducting qubit systems.

Findings

Increased leakage mobility improves quantum stability performance.

Standard error-correction circuits outperform patch wiggling with high leakage mobility.

Leakage damage can be mitigated by stimulating leakage mobility without dedicated units.

Abstract

Leakage from the computational subspace is a damaging source of noise that degrades the performance of most qubit types. Unlike other types of noise, leakage cannot be overcome by standard quantum error correction techniques and requires dedicated leakage reduction units. In this work, we study the effects of leakage mobility between superconducting qubits on the performance of a quantum stability experiment, which is a benchmark for fault-tolerant logical computation. Using the Fujitsu Quantum Simulator, we perform full density-matrix simulations of stability experiments implemented on the surface code. We observe improved performance with increased mobility, suggesting leakage mobility can itself act as a leakage reduction unit by naturally moving leakage from data to auxiliary qubits, where it is removed upon reset. We compare the performance of standard error-correction circuits with "patch wiggling", a specific leakage reduction technique where data and auxiliary qubits alternate their roles in each round of error correction. We observe that patch wiggling becomes inefficient with increased leakage mobility, in contrast to the improved performance of standard circuits. These observations suggest that the damage of leakage can be overcome by stimulating leakage mobility between qubits without the need for a dedicated leakage reduction unit.