Fault-Tolerant Cut-Cat State Syndrome Extraction for Quantum Codes

TL;DR

This paper introduces a fault-tolerant syndrome extraction method called the cut-cat state scheme for quantum error correction, reducing qubit requirements and gate counts compared to existing protocols.

Contribution

The novel cut-cat state scheme improves fault-tolerance in quantum syndrome extraction by combining parallelized interactions with reduced qubit and gate overhead.

Findings

Reduces the number of simultaneous qubits by over 50%.

Offers lower two-qubit gate count than flag-based protocols as code distance grows.

Maintains parallelized data qubit interactions with added stabilizer measurements.

Abstract

Reliable quantum computation requires fault-tolerant protocols to prevent errors from propagating during syndrome extraction in quantum error correction. We present a novel fault-tolerant syndrome extraction technique for CSS codes, which we refer to as the cut-cat state scheme. While each ancilla qubit interacts non-fault-tolerantly with a pair of data qubits, we introduce additional cat stabilizer measurements to identify and correct the resulting hook errors. Our approach maintains the key benefit of cat-based extraction, i.e., parallelized data qubit interactions, while reducing the number of simultaneous qubits required by more than half. Compared to flag-based state-of-the-art protocols, the cut-cat scheme offers a notable advantage in terms of two-qubit gate count as the code distance increases.