Triangular color codes on trivalent graphs with flag qubits

TL;DR

This paper investigates the fault-tolerance threshold of the triangular color code with flag qubits, adapting decoding methods and proposing implementations to improve quantum error correction in superconducting hardware.

Contribution

It introduces a fault-tolerant stabilizer measurement scheme with flag qubits and estimates the code's threshold at 0.2%, advancing practical quantum error correction.

Findings

Threshold estimated at 0.2% under circuit-level depolarizing noise

Flag qubits enable preservation of full code distance with simplified circuits

Adapted Restriction Decoder for triangular color codes

Abstract

The color code is a topological quantum error-correcting code supporting a variety of valuable fault-tolerant logical gates. Its two-dimensional version, the triangular color code, may soon be realized with currently available superconducting hardware despite constrained qubit connectivity. To guide this experimental effort, we study the storage threshold of the triangular color code against circuit-level depolarizing noise. First, we adapt the Restriction Decoder to the setting of the triangular color code and to phenomenological noise. Then, we propose a fault-tolerant implementation of the stabilizer measurement circuits, which incorporates flag qubits. We show how information from flag qubits can be used with the Restriction Decoder to maintain the effective distance of the code. We numerically estimate the threshold of the triangular color code to be 0.2%, which is competitive with the thresholds of other topological quantum codes. We also prove that 1-flag stabilizer measurement circuits are sufficient to preserve the full code distance, which may be used to find simpler syndrome extraction circuits of the color code.