High-performance repetition cat code using fast noisy operations

TL;DR

This paper enhances the repetition cat code architecture by optimizing the use of fast, noisy CNOT gates for stabilizer measurements, achieving high thresholds and efficient scaling for fault-tolerant quantum computing.

Contribution

It introduces a performance optimization leveraging fast, low-fidelity CNOT gates and ancilla qubits, improving error thresholds and scalability in cat qubit-based quantum processors.

Findings

High thresholds for physical figure of merit achieved.

Efficient scaling below threshold for logical error rates.

Robustness against leakage and fast operation errors.

Abstract

Bosonic cat qubits stabilized by two-photon driven dissipation benefit from exponential suppression of bit-flip errors and an extensive set of gates preserving this protection. These properties make them promising building blocks of a hardware-efficient and fault-tolerant quantum processor. In this paper, we propose a performance optimization of the repetition cat code architecture using fast but noisy CNOT gates for stabilizer measurements. This optimization leads to high thresholds for the physical figure of merit, given as the ratio between intrinsic single-photon loss rate of the bosonic mode and the engineered two-photon loss rate, as well as a very interesting scaling below threshold of the required overhead, to reach an expected level of logical error rate. Relying on the specific error models for cat qubit operations, this optimization exploits fast parity measurements, using accelerated low-fidelity CNOT gates, combined with fast ancilla parity-check qubits. The significant enhancement in the performance is explained by: 1- the highly asymmetric error model of cat qubit CNOT gates with a major component on control (ancilla) qubits, and 2- the robustness of the error correction performance in presence of the leakage induced by fast operations. In order to demonstrate these performances, we develop a method to sample the repetition code under circuit-level noise that also takes into account cat qubit state leakage.