Adaptive framework for failure-aware protocols in fusion-based graph-state generation

We consider the generation of photonic graph states in a linear optics setting where sequential nondeterministic fusion measurements are used to build large graph states out of small linear clusters and develop a framework to optimize the building process using graph-theoretic characterizations of fusion networks. We present graph-state generation protocols for linear cluster resource states and type-I/type-II fusions which are adaptive to fusion failure, that is, they reuse leftover graph states in the remaining building process. To estimate hardware costs, we interpret our protocols as finite Markov processes. This viewpoint allows us to cast the expected number of fusion measurements until success as a problem. We then deploy a pipeline of polynomial algorithms to optimize arbitrary graph states, extract fusion networks, and find beneficial orderings of fusions. We check the effectiveness of these algorithms by verifying that the corresponding are decreased. We evaluate our pipeline for different initial resource states and fusion mechanisms with varying success probabilities. Results show reductions in the fusion overhead by several orders of magnitude when compared to simple repeat until success protocols and by up to 40 % when compared to state-of-the-art graph-state generation protocols, especially for realistic fusion success probabilities between 50% and 75%.