Abstract Body

Leakage of quantum information out of the two computational states of a qubit into other energy states represents a major challenge in the pursuit of quantum error correction. During an error-corrected algorithm, leakage builds over time and spreads through multi-qubit interactions. This leads to correlated errors that degrade the exponential suppression of logical error with scale, challenging the feasibility of quantum error correction as a path towards fault-tolerant quantum computation. Here, we demonstrate a distance-3 surface code and distance-21 bit-flip code on a quantum processor where leakage is removed from all qubits in each cycle. This shortens the lifetime of leakage and curtails its ability to spread and induce correlated errors. We report a ten-fold reduction in steady-state leakage population on the data qubits encoding the logical state and an average leakage population of less than 1×10^-3 throughout the entire device. Our leakage removal process efficiently returns the system back to the computational basis, and adding it to a code circuit prevents leakage from inducing correlated error across cycles. With this demonstration that leakage can be contained, we resolve a key challenge for practical quantum error correction at scale.

References

Overcoming leakage in scalable quantum error correction, K.C. Miao, M. McEwen, et al.,
https://arxiv.org/abs/2211.04728

Acknowledgment

We acknowledge the Google Quantum AI hardware team for device fabrication, as well as experimental set-up, operation, and maintenance.