Deterministic generation of concatenated graph codes from quantum emitters

Abstract: Photon loss is the dominant noise mechanism in photonic quantum technologies. Designing fault-tolerant schemes with high tolerance to loss is thus a central challenge in scaling photonic quantum information processors. Concatenation of a fault-tolerant construction with a code able to efficiently correct loss is a promising approach to achieve this, but practical ways to implement code concatenation with photons have been lacking. We propose schemes for generating concatenated graph codes using multi-photon emission from two quantum emitters or a single quantum emitter coupled to a memory; capabilities available in several photonic platforms. We show that these schemes enable fault-tolerant fusion-based quantum computation in practical regimes with high photon loss and standard fusion gates without the need for auxiliary photons.